CVE-2021-46933 (GCVE-0-2021-46933)

Vulnerability from cvelistv5 – Published: 2024-02-27 09:44 – Updated: 2026-05-11 13:44
VLAI
Title
usb: gadget: f_fs: Clear ffs_eventfd in ffs_data_clear.
Summary
In the Linux kernel, the following vulnerability has been resolved: usb: gadget: f_fs: Clear ffs_eventfd in ffs_data_clear. ffs_data_clear is indirectly called from both ffs_fs_kill_sb and ffs_ep0_release, so it ends up being called twice when userland closes ep0 and then unmounts f_fs. If userland provided an eventfd along with function's USB descriptors, it ends up calling eventfd_ctx_put as many times, causing a refcount underflow. NULL-ify ffs_eventfd to prevent these extraneous eventfd_ctx_put calls. Also, set epfiles to NULL right after de-allocating it, for readability. For completeness, ffs_data_clear actually ends up being called thrice, the last call being before the whole ffs structure gets freed, so when this specific sequence happens there is a second underflow happening (but not being reported): /sys/kernel/debug/tracing# modprobe usb_f_fs /sys/kernel/debug/tracing# echo ffs_data_clear > set_ftrace_filter /sys/kernel/debug/tracing# echo function > current_tracer /sys/kernel/debug/tracing# echo 1 > tracing_on (setup gadget, run and kill function userland process, teardown gadget) /sys/kernel/debug/tracing# echo 0 > tracing_on /sys/kernel/debug/tracing# cat trace smartcard-openp-436 [000] ..... 1946.208786: ffs_data_clear <-ffs_data_closed smartcard-openp-431 [000] ..... 1946.279147: ffs_data_clear <-ffs_data_closed smartcard-openp-431 [000] .n... 1946.905512: ffs_data_clear <-ffs_data_put Warning output corresponding to above trace: [ 1946.284139] WARNING: CPU: 0 PID: 431 at lib/refcount.c:28 refcount_warn_saturate+0x110/0x15c [ 1946.293094] refcount_t: underflow; use-after-free. [ 1946.298164] Modules linked in: usb_f_ncm(E) u_ether(E) usb_f_fs(E) hci_uart(E) btqca(E) btrtl(E) btbcm(E) btintel(E) bluetooth(E) nls_ascii(E) nls_cp437(E) vfat(E) fat(E) bcm2835_v4l2(CE) bcm2835_mmal_vchiq(CE) videobuf2_vmalloc(E) videobuf2_memops(E) sha512_generic(E) videobuf2_v4l2(E) sha512_arm(E) videobuf2_common(E) videodev(E) cpufreq_dt(E) snd_bcm2835(CE) brcmfmac(E) mc(E) vc4(E) ctr(E) brcmutil(E) snd_soc_core(E) snd_pcm_dmaengine(E) drbg(E) snd_pcm(E) snd_timer(E) snd(E) soundcore(E) drm_kms_helper(E) cec(E) ansi_cprng(E) rc_core(E) syscopyarea(E) raspberrypi_cpufreq(E) sysfillrect(E) sysimgblt(E) cfg80211(E) max17040_battery(OE) raspberrypi_hwmon(E) fb_sys_fops(E) regmap_i2c(E) ecdh_generic(E) rfkill(E) ecc(E) bcm2835_rng(E) rng_core(E) vchiq(CE) leds_gpio(E) libcomposite(E) fuse(E) configfs(E) ip_tables(E) x_tables(E) autofs4(E) ext4(E) crc16(E) mbcache(E) jbd2(E) crc32c_generic(E) sdhci_iproc(E) sdhci_pltfm(E) sdhci(E) [ 1946.399633] CPU: 0 PID: 431 Comm: smartcard-openp Tainted: G C OE 5.15.0-1-rpi #1 Debian 5.15.3-1 [ 1946.417950] Hardware name: BCM2835 [ 1946.425442] Backtrace: [ 1946.432048] [<c08d60a0>] (dump_backtrace) from [<c08d62ec>] (show_stack+0x20/0x24) [ 1946.448226] r7:00000009 r6:0000001c r5:c04a948c r4:c0a64e2c [ 1946.458412] [<c08d62cc>] (show_stack) from [<c08d9ae0>] (dump_stack+0x28/0x30) [ 1946.470380] [<c08d9ab8>] (dump_stack) from [<c0123500>] (__warn+0xe8/0x154) [ 1946.482067] r5:c04a948c r4:c0a71dc8 [ 1946.490184] [<c0123418>] (__warn) from [<c08d6948>] (warn_slowpath_fmt+0xa0/0xe4) [ 1946.506758] r7:00000009 r6:0000001c r5:c0a71dc8 r4:c0a71e04 [ 1946.517070] [<c08d68ac>] (warn_slowpath_fmt) from [<c04a948c>] (refcount_warn_saturate+0x110/0x15c) [ 1946.535309] r8:c0100224 r7:c0dfcb84 r6:ffffffff r5:c3b84c00 r4:c24a17c0 [ 1946.546708] [<c04a937c>] (refcount_warn_saturate) from [<c0380134>] (eventfd_ctx_put+0x48/0x74) [ 1946.564476] [<c03800ec>] (eventfd_ctx_put) from [<bf5464e8>] (ffs_data_clear+0xd0/0x118 [usb_f_fs]) [ 1946.582664] r5:c3b84c00 r4:c2695b00 [ 1946.590668] [<bf546418>] (ffs_data_clear [usb_f_fs]) from [<bf547cc0>] (ffs_data_closed+0x9c/0x150 [usb_f_fs]) [ 1946.609608] r5:bf54d014 r4:c2695b00 [ 1946.617522] [<bf547c24>] (ffs_data_closed [usb_f_fs]) from [<bf547da0>] (ffs_fs_kill_sb+0x2c/0x30 [usb_f_fs]) [ 1946.636217] r7:c0dfcb ---truncated---
Severity
5.5 (Medium)
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
SSVC
Exploitation: none Automatable: no Technical Impact: partial
CISA Coordinator (v2.0.3)
CWE
  • CWE-476 - NULL Pointer Dereference
Assigner
References
Impacted products
Vendor Product Version
Linux Linux Affected: 5e33f6fdf735cda1d4580fe6f1878da05718fe73 , < f976dd7011150244a7ba820f2c331e9fb253befa (git)
Affected: 5e33f6fdf735cda1d4580fe6f1878da05718fe73 , < cc8c8028c21b2a3842a1e98e99e55028df275919 (git)
Affected: 5e33f6fdf735cda1d4580fe6f1878da05718fe73 , < 52500239e3f2d6fc77b6f58632a9fb98fe74ac09 (git)
Affected: 5e33f6fdf735cda1d4580fe6f1878da05718fe73 , < 33f6a0cbb7772146e1c11f38028fffbfed14728b (git)
Affected: 5e33f6fdf735cda1d4580fe6f1878da05718fe73 , < 240fc586e83d645912accce081a48aa63a45f6ee (git)
Affected: 5e33f6fdf735cda1d4580fe6f1878da05718fe73 , < 1c4ace3e6b8575745c50dca9e76e0021e697d645 (git)
Affected: 5e33f6fdf735cda1d4580fe6f1878da05718fe73 , < ebef2aa29f370b5096c16020c104e393192ef684 (git)
Affected: 5e33f6fdf735cda1d4580fe6f1878da05718fe73 , < b1e0887379422975f237d43d8839b751a6bcf154 (git)
Create a notification for this product.
Linux Linux Affected: 4.0
Unaffected: 0 , < 4.0 (semver)
Unaffected: 4.4.298 , ≤ 4.4.* (semver)
Unaffected: 4.9.296 , ≤ 4.9.* (semver)
Unaffected: 4.14.261 , ≤ 4.14.* (semver)
Unaffected: 4.19.224 , ≤ 4.19.* (semver)
Unaffected: 5.4.170 , ≤ 5.4.* (semver)
Unaffected: 5.10.90 , ≤ 5.10.* (semver)
Unaffected: 5.15.13 , ≤ 5.15.* (semver)
Unaffected: 5.16 , ≤ * (original_commit_for_fix)
Create a notification for this product.
Show details on NVD website
To clipboard 

{
  "containers": {
    "adp": [
      {
        "metrics": [
          {
            "cvssV3_1": {
              "attackComplexity": "LOW",
              "attackVector": "LOCAL",
              "availabilityImpact": "HIGH",
              "baseScore": 5.5,
              "baseSeverity": "MEDIUM",
              "confidentialityImpact": "NONE",
              "integrityImpact": "NONE",
              "privilegesRequired": "LOW",
              "scope": "UNCHANGED",
              "userInteraction": "NONE",
              "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H",
              "version": "3.1"
            }
          },
          {
            "other": {
              "content": {
                "id": "CVE-2021-46933",
                "options": [
                  {
                    "Exploitation": "none"
                  },
                  {
                    "Automatable": "no"
                  },
                  {
                    "Technical Impact": "partial"
                  }
                ],
                "role": "CISA Coordinator",
                "timestamp": "2025-04-22T16:12:25.365291Z",
                "version": "2.0.3"
              },
              "type": "ssvc"
            }
          }
        ],
        "problemTypes": [
          {
            "descriptions": [
              {
                "cweId": "CWE-476",
                "description": "CWE-476 NULL Pointer Dereference",
                "lang": "en",
                "type": "CWE"
              }
            ]
          }
        ],
        "providerMetadata": {
          "dateUpdated": "2025-04-22T16:12:28.882Z",
          "orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
          "shortName": "CISA-ADP"
        },
        "title": "CISA ADP Vulnrichment"
      },
      {
        "providerMetadata": {
          "dateUpdated": "2024-08-04T05:17:43.071Z",
          "orgId": "af854a3a-2127-422b-91ae-364da2661108",
          "shortName": "CVE"
        },
        "references": [
          {
            "tags": [
              "x_transferred"
            ],
            "url": "https://git.kernel.org/stable/c/f976dd7011150244a7ba820f2c331e9fb253befa"
          },
          {
            "tags": [
              "x_transferred"
            ],
            "url": "https://git.kernel.org/stable/c/cc8c8028c21b2a3842a1e98e99e55028df275919"
          },
          {
            "tags": [
              "x_transferred"
            ],
            "url": "https://git.kernel.org/stable/c/52500239e3f2d6fc77b6f58632a9fb98fe74ac09"
          },
          {
            "tags": [
              "x_transferred"
            ],
            "url": "https://git.kernel.org/stable/c/33f6a0cbb7772146e1c11f38028fffbfed14728b"
          },
          {
            "tags": [
              "x_transferred"
            ],
            "url": "https://git.kernel.org/stable/c/240fc586e83d645912accce081a48aa63a45f6ee"
          },
          {
            "tags": [
              "x_transferred"
            ],
            "url": "https://git.kernel.org/stable/c/1c4ace3e6b8575745c50dca9e76e0021e697d645"
          },
          {
            "tags": [
              "x_transferred"
            ],
            "url": "https://git.kernel.org/stable/c/ebef2aa29f370b5096c16020c104e393192ef684"
          },
          {
            "tags": [
              "x_transferred"
            ],
            "url": "https://git.kernel.org/stable/c/b1e0887379422975f237d43d8839b751a6bcf154"
          }
        ],
        "title": "CVE Program Container"
      }
    ],
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "drivers/usb/gadget/function/f_fs.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "lessThan": "f976dd7011150244a7ba820f2c331e9fb253befa",
              "status": "affected",
              "version": "5e33f6fdf735cda1d4580fe6f1878da05718fe73",
              "versionType": "git"
            },
            {
              "lessThan": "cc8c8028c21b2a3842a1e98e99e55028df275919",
              "status": "affected",
              "version": "5e33f6fdf735cda1d4580fe6f1878da05718fe73",
              "versionType": "git"
            },
            {
              "lessThan": "52500239e3f2d6fc77b6f58632a9fb98fe74ac09",
              "status": "affected",
              "version": "5e33f6fdf735cda1d4580fe6f1878da05718fe73",
              "versionType": "git"
            },
            {
              "lessThan": "33f6a0cbb7772146e1c11f38028fffbfed14728b",
              "status": "affected",
              "version": "5e33f6fdf735cda1d4580fe6f1878da05718fe73",
              "versionType": "git"
            },
            {
              "lessThan": "240fc586e83d645912accce081a48aa63a45f6ee",
              "status": "affected",
              "version": "5e33f6fdf735cda1d4580fe6f1878da05718fe73",
              "versionType": "git"
            },
            {
              "lessThan": "1c4ace3e6b8575745c50dca9e76e0021e697d645",
              "status": "affected",
              "version": "5e33f6fdf735cda1d4580fe6f1878da05718fe73",
              "versionType": "git"
            },
            {
              "lessThan": "ebef2aa29f370b5096c16020c104e393192ef684",
              "status": "affected",
              "version": "5e33f6fdf735cda1d4580fe6f1878da05718fe73",
              "versionType": "git"
            },
            {
              "lessThan": "b1e0887379422975f237d43d8839b751a6bcf154",
              "status": "affected",
              "version": "5e33f6fdf735cda1d4580fe6f1878da05718fe73",
              "versionType": "git"
            }
          ]
        },
        {
          "defaultStatus": "affected",
          "product": "Linux",
          "programFiles": [
            "drivers/usb/gadget/function/f_fs.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "status": "affected",
              "version": "4.0"
            },
            {
              "lessThan": "4.0",
              "status": "unaffected",
              "version": "0",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "4.4.*",
              "status": "unaffected",
              "version": "4.4.298",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "4.9.*",
              "status": "unaffected",
              "version": "4.9.296",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "4.14.*",
              "status": "unaffected",
              "version": "4.14.261",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "4.19.*",
              "status": "unaffected",
              "version": "4.19.224",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "5.4.*",
              "status": "unaffected",
              "version": "5.4.170",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "5.10.*",
              "status": "unaffected",
              "version": "5.10.90",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "5.15.*",
              "status": "unaffected",
              "version": "5.15.13",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "*",
              "status": "unaffected",
              "version": "5.16",
              "versionType": "original_commit_for_fix"
            }
          ]
        }
      ],
      "cpeApplicability": [
        {
          "nodes": [
            {
              "cpeMatch": [
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "4.4.298",
                  "versionStartIncluding": "4.0",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "4.9.296",
                  "versionStartIncluding": "4.0",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "4.14.261",
                  "versionStartIncluding": "4.0",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "4.19.224",
                  "versionStartIncluding": "4.0",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "5.4.170",
                  "versionStartIncluding": "4.0",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "5.10.90",
                  "versionStartIncluding": "4.0",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "5.15.13",
                  "versionStartIncluding": "4.0",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "5.16",
                  "versionStartIncluding": "4.0",
                  "vulnerable": true
                }
              ],
              "negate": false,
              "operator": "OR"
            }
          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nusb: gadget: f_fs: Clear ffs_eventfd in ffs_data_clear.\n\nffs_data_clear is indirectly called from both ffs_fs_kill_sb and\nffs_ep0_release, so it ends up being called twice when userland closes ep0\nand then unmounts f_fs.\nIf userland provided an eventfd along with function\u0027s USB descriptors, it\nends up calling eventfd_ctx_put as many times, causing a refcount\nunderflow.\nNULL-ify ffs_eventfd to prevent these extraneous eventfd_ctx_put calls.\n\nAlso, set epfiles to NULL right after de-allocating it, for readability.\n\nFor completeness, ffs_data_clear actually ends up being called thrice, the\nlast call being before the whole ffs structure gets freed, so when this\nspecific sequence happens there is a second underflow happening (but not\nbeing reported):\n\n/sys/kernel/debug/tracing# modprobe usb_f_fs\n/sys/kernel/debug/tracing# echo ffs_data_clear \u003e set_ftrace_filter\n/sys/kernel/debug/tracing# echo function \u003e current_tracer\n/sys/kernel/debug/tracing# echo 1 \u003e tracing_on\n(setup gadget, run and kill function userland process, teardown gadget)\n/sys/kernel/debug/tracing# echo 0 \u003e tracing_on\n/sys/kernel/debug/tracing# cat trace\n smartcard-openp-436     [000] .....  1946.208786: ffs_data_clear \u003c-ffs_data_closed\n smartcard-openp-431     [000] .....  1946.279147: ffs_data_clear \u003c-ffs_data_closed\n smartcard-openp-431     [000] .n...  1946.905512: ffs_data_clear \u003c-ffs_data_put\n\nWarning output corresponding to above trace:\n[ 1946.284139] WARNING: CPU: 0 PID: 431 at lib/refcount.c:28 refcount_warn_saturate+0x110/0x15c\n[ 1946.293094] refcount_t: underflow; use-after-free.\n[ 1946.298164] Modules linked in: usb_f_ncm(E) u_ether(E) usb_f_fs(E) hci_uart(E) btqca(E) btrtl(E) btbcm(E) btintel(E) bluetooth(E) nls_ascii(E) nls_cp437(E) vfat(E) fat(E) bcm2835_v4l2(CE) bcm2835_mmal_vchiq(CE) videobuf2_vmalloc(E) videobuf2_memops(E) sha512_generic(E) videobuf2_v4l2(E) sha512_arm(E) videobuf2_common(E) videodev(E) cpufreq_dt(E) snd_bcm2835(CE) brcmfmac(E) mc(E) vc4(E) ctr(E) brcmutil(E) snd_soc_core(E) snd_pcm_dmaengine(E) drbg(E) snd_pcm(E) snd_timer(E) snd(E) soundcore(E) drm_kms_helper(E) cec(E) ansi_cprng(E) rc_core(E) syscopyarea(E) raspberrypi_cpufreq(E) sysfillrect(E) sysimgblt(E) cfg80211(E) max17040_battery(OE) raspberrypi_hwmon(E) fb_sys_fops(E) regmap_i2c(E) ecdh_generic(E) rfkill(E) ecc(E) bcm2835_rng(E) rng_core(E) vchiq(CE) leds_gpio(E) libcomposite(E) fuse(E) configfs(E) ip_tables(E) x_tables(E) autofs4(E) ext4(E) crc16(E) mbcache(E) jbd2(E) crc32c_generic(E) sdhci_iproc(E) sdhci_pltfm(E) sdhci(E)\n[ 1946.399633] CPU: 0 PID: 431 Comm: smartcard-openp Tainted: G         C OE     5.15.0-1-rpi #1  Debian 5.15.3-1\n[ 1946.417950] Hardware name: BCM2835\n[ 1946.425442] Backtrace:\n[ 1946.432048] [\u003cc08d60a0\u003e] (dump_backtrace) from [\u003cc08d62ec\u003e] (show_stack+0x20/0x24)\n[ 1946.448226]  r7:00000009 r6:0000001c r5:c04a948c r4:c0a64e2c\n[ 1946.458412] [\u003cc08d62cc\u003e] (show_stack) from [\u003cc08d9ae0\u003e] (dump_stack+0x28/0x30)\n[ 1946.470380] [\u003cc08d9ab8\u003e] (dump_stack) from [\u003cc0123500\u003e] (__warn+0xe8/0x154)\n[ 1946.482067]  r5:c04a948c r4:c0a71dc8\n[ 1946.490184] [\u003cc0123418\u003e] (__warn) from [\u003cc08d6948\u003e] (warn_slowpath_fmt+0xa0/0xe4)\n[ 1946.506758]  r7:00000009 r6:0000001c r5:c0a71dc8 r4:c0a71e04\n[ 1946.517070] [\u003cc08d68ac\u003e] (warn_slowpath_fmt) from [\u003cc04a948c\u003e] (refcount_warn_saturate+0x110/0x15c)\n[ 1946.535309]  r8:c0100224 r7:c0dfcb84 r6:ffffffff r5:c3b84c00 r4:c24a17c0\n[ 1946.546708] [\u003cc04a937c\u003e] (refcount_warn_saturate) from [\u003cc0380134\u003e] (eventfd_ctx_put+0x48/0x74)\n[ 1946.564476] [\u003cc03800ec\u003e] (eventfd_ctx_put) from [\u003cbf5464e8\u003e] (ffs_data_clear+0xd0/0x118 [usb_f_fs])\n[ 1946.582664]  r5:c3b84c00 r4:c2695b00\n[ 1946.590668] [\u003cbf546418\u003e] (ffs_data_clear [usb_f_fs]) from [\u003cbf547cc0\u003e] (ffs_data_closed+0x9c/0x150 [usb_f_fs])\n[ 1946.609608]  r5:bf54d014 r4:c2695b00\n[ 1946.617522] [\u003cbf547c24\u003e] (ffs_data_closed [usb_f_fs]) from [\u003cbf547da0\u003e] (ffs_fs_kill_sb+0x2c/0x30 [usb_f_fs])\n[ 1946.636217]  r7:c0dfcb\n---truncated---"
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-05-11T13:44:42.774Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/f976dd7011150244a7ba820f2c331e9fb253befa"
        },
        {
          "url": "https://git.kernel.org/stable/c/cc8c8028c21b2a3842a1e98e99e55028df275919"
        },
        {
          "url": "https://git.kernel.org/stable/c/52500239e3f2d6fc77b6f58632a9fb98fe74ac09"
        },
        {
          "url": "https://git.kernel.org/stable/c/33f6a0cbb7772146e1c11f38028fffbfed14728b"
        },
        {
          "url": "https://git.kernel.org/stable/c/240fc586e83d645912accce081a48aa63a45f6ee"
        },
        {
          "url": "https://git.kernel.org/stable/c/1c4ace3e6b8575745c50dca9e76e0021e697d645"
        },
        {
          "url": "https://git.kernel.org/stable/c/ebef2aa29f370b5096c16020c104e393192ef684"
        },
        {
          "url": "https://git.kernel.org/stable/c/b1e0887379422975f237d43d8839b751a6bcf154"
        }
      ],
      "title": "usb: gadget: f_fs: Clear ffs_eventfd in ffs_data_clear.",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2021-46933",
    "datePublished": "2024-02-27T09:44:00.758Z",
    "dateReserved": "2024-02-25T13:45:52.720Z",
    "dateUpdated": "2026-05-11T13:44:42.774Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2",
  "vulnerability-lookup:meta": {
    "epss": {
      "cve": "CVE-2021-46933",
      "date": "2026-07-26",
      "epss": "0.00233",
      "percentile": "0.14311"
    },
    "fkie_nvd": {
      "configurations": "[{\"nodes\": [{\"operator\": \"OR\", \"negate\": false, \"cpeMatch\": [{\"vulnerable\": true, \"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"versionStartIncluding\": \"4.0.0\", \"versionEndExcluding\": \"4.4.298\", \"matchCriteriaId\": \"C01E3FB6-531E-4ABC-BF95-6FADD48AE7E0\"}, {\"vulnerable\": true, \"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"versionStartIncluding\": \"4.5.0\", \"versionEndExcluding\": \"4.9.296\", \"matchCriteriaId\": \"883CB22B-11DA-4D54-8121-3F5494EDBD4C\"}, {\"vulnerable\": true, \"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"versionStartIncluding\": \"4.10.0\", \"versionEndExcluding\": \"4.14.261\", \"matchCriteriaId\": \"B5D4F856-5F69-4F4A-911F-50A21B9A68B6\"}, {\"vulnerable\": true, \"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"versionStartIncluding\": \"4.15.0\", \"versionEndExcluding\": \"4.19.224\", \"matchCriteriaId\": \"B34A1353-506A-4AB9-87EC-CD50F09DFB8A\"}, {\"vulnerable\": true, \"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"versionStartIncluding\": \"4.20.0\", \"versionEndExcluding\": \"5.4.170\", \"matchCriteriaId\": \"56D16FBB-453E-4316-A027-E517828203D7\"}, {\"vulnerable\": true, \"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"versionStartIncluding\": \"5.5.0\", \"versionEndExcluding\": \"5.10.90\", \"matchCriteriaId\": \"C87FB3FD-3E74-4588-A1A4-B9BA8AE0C06B\"}, {\"vulnerable\": true, \"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"versionStartIncluding\": \"5.11.0\", \"versionEndExcluding\": \"5.15.13\", \"matchCriteriaId\": \"083E0940-932B-447B-A6B2-677DAE27FD04\"}]}]}]",
      "descriptions": "[{\"lang\": \"en\", \"value\": \"In the Linux kernel, the following vulnerability has been resolved:\\n\\nusb: gadget: f_fs: Clear ffs_eventfd in ffs_data_clear.\\n\\nffs_data_clear is indirectly called from both ffs_fs_kill_sb and\\nffs_ep0_release, so it ends up being called twice when userland closes ep0\\nand then unmounts f_fs.\\nIf userland provided an eventfd along with function\u0027s USB descriptors, it\\nends up calling eventfd_ctx_put as many times, causing a refcount\\nunderflow.\\nNULL-ify ffs_eventfd to prevent these extraneous eventfd_ctx_put calls.\\n\\nAlso, set epfiles to NULL right after de-allocating it, for readability.\\n\\nFor completeness, ffs_data_clear actually ends up being called thrice, the\\nlast call being before the whole ffs structure gets freed, so when this\\nspecific sequence happens there is a second underflow happening (but not\\nbeing reported):\\n\\n/sys/kernel/debug/tracing# modprobe usb_f_fs\\n/sys/kernel/debug/tracing# echo ffs_data_clear \u003e set_ftrace_filter\\n/sys/kernel/debug/tracing# echo function \u003e current_tracer\\n/sys/kernel/debug/tracing# echo 1 \u003e tracing_on\\n(setup gadget, run and kill function userland process, teardown gadget)\\n/sys/kernel/debug/tracing# echo 0 \u003e tracing_on\\n/sys/kernel/debug/tracing# cat trace\\n smartcard-openp-436     [000] .....  1946.208786: ffs_data_clear \u003c-ffs_data_closed\\n smartcard-openp-431     [000] .....  1946.279147: ffs_data_clear \u003c-ffs_data_closed\\n smartcard-openp-431     [000] .n...  1946.905512: ffs_data_clear \u003c-ffs_data_put\\n\\nWarning output corresponding to above trace:\\n[ 1946.284139] WARNING: CPU: 0 PID: 431 at lib/refcount.c:28 refcount_warn_saturate+0x110/0x15c\\n[ 1946.293094] refcount_t: underflow; use-after-free.\\n[ 1946.298164] Modules linked in: usb_f_ncm(E) u_ether(E) usb_f_fs(E) hci_uart(E) btqca(E) btrtl(E) btbcm(E) btintel(E) bluetooth(E) nls_ascii(E) nls_cp437(E) vfat(E) fat(E) bcm2835_v4l2(CE) bcm2835_mmal_vchiq(CE) videobuf2_vmalloc(E) videobuf2_memops(E) sha512_generic(E) videobuf2_v4l2(E) sha512_arm(E) videobuf2_common(E) videodev(E) cpufreq_dt(E) snd_bcm2835(CE) brcmfmac(E) mc(E) vc4(E) ctr(E) brcmutil(E) snd_soc_core(E) snd_pcm_dmaengine(E) drbg(E) snd_pcm(E) snd_timer(E) snd(E) soundcore(E) drm_kms_helper(E) cec(E) ansi_cprng(E) rc_core(E) syscopyarea(E) raspberrypi_cpufreq(E) sysfillrect(E) sysimgblt(E) cfg80211(E) max17040_battery(OE) raspberrypi_hwmon(E) fb_sys_fops(E) regmap_i2c(E) ecdh_generic(E) rfkill(E) ecc(E) bcm2835_rng(E) rng_core(E) vchiq(CE) leds_gpio(E) libcomposite(E) fuse(E) configfs(E) ip_tables(E) x_tables(E) autofs4(E) ext4(E) crc16(E) mbcache(E) jbd2(E) crc32c_generic(E) sdhci_iproc(E) sdhci_pltfm(E) sdhci(E)\\n[ 1946.399633] CPU: 0 PID: 431 Comm: smartcard-openp Tainted: G         C OE     5.15.0-1-rpi #1  Debian 5.15.3-1\\n[ 1946.417950] Hardware name: BCM2835\\n[ 1946.425442] Backtrace:\\n[ 1946.432048] [\u003cc08d60a0\u003e] (dump_backtrace) from [\u003cc08d62ec\u003e] (show_stack+0x20/0x24)\\n[ 1946.448226]  r7:00000009 r6:0000001c r5:c04a948c r4:c0a64e2c\\n[ 1946.458412] [\u003cc08d62cc\u003e] (show_stack) from [\u003cc08d9ae0\u003e] (dump_stack+0x28/0x30)\\n[ 1946.470380] [\u003cc08d9ab8\u003e] (dump_stack) from [\u003cc0123500\u003e] (__warn+0xe8/0x154)\\n[ 1946.482067]  r5:c04a948c r4:c0a71dc8\\n[ 1946.490184] [\u003cc0123418\u003e] (__warn) from [\u003cc08d6948\u003e] (warn_slowpath_fmt+0xa0/0xe4)\\n[ 1946.506758]  r7:00000009 r6:0000001c r5:c0a71dc8 r4:c0a71e04\\n[ 1946.517070] [\u003cc08d68ac\u003e] (warn_slowpath_fmt) from [\u003cc04a948c\u003e] (refcount_warn_saturate+0x110/0x15c)\\n[ 1946.535309]  r8:c0100224 r7:c0dfcb84 r6:ffffffff r5:c3b84c00 r4:c24a17c0\\n[ 1946.546708] [\u003cc04a937c\u003e] (refcount_warn_saturate) from [\u003cc0380134\u003e] (eventfd_ctx_put+0x48/0x74)\\n[ 1946.564476] [\u003cc03800ec\u003e] (eventfd_ctx_put) from [\u003cbf5464e8\u003e] (ffs_data_clear+0xd0/0x118 [usb_f_fs])\\n[ 1946.582664]  r5:c3b84c00 r4:c2695b00\\n[ 1946.590668] [\u003cbf546418\u003e] (ffs_data_clear [usb_f_fs]) from [\u003cbf547cc0\u003e] (ffs_data_closed+0x9c/0x150 [usb_f_fs])\\n[ 1946.609608]  r5:bf54d014 r4:c2695b00\\n[ 1946.617522] [\u003cbf547c24\u003e] (ffs_data_closed [usb_f_fs]) from [\u003cbf547da0\u003e] (ffs_fs_kill_sb+0x2c/0x30 [usb_f_fs])\\n[ 1946.636217]  r7:c0dfcb\\n---truncated---\"}, {\"lang\": \"es\", \"value\": \"En el kernel de Linux se ha resuelto la siguiente vulnerabilidad: usb: gadget: f_fs: Borrar ffs_eventfd en ffs_data_clear. ffs_data_clear se llama indirectamente desde ffs_fs_kill_sb y ffs_ep0_release, por lo que termina siendo llamado dos veces cuando el \\u00e1rea de usuario cierra ep0 y luego desmonta f_fs. Si Userland proporcion\\u00f3 un eventfd junto con los descriptores USB de la funci\\u00f3n, termina llamando a eventfd_ctx_put tantas veces, provocando un desbordamiento insuficiente de recuento. NULL-ify ffs_eventfd para evitar estas llamadas extra\\u00f1as eventfd_ctx_put. Adem\\u00e1s, establezca epfiles en NULL justo despu\\u00e9s de desasignarlo, para facilitar la lectura. Para completar, ffs_data_clear en realidad termina siendo llamado tres veces, la \\u00faltima llamada es antes de que se libere toda la estructura de ffs, por lo que cuando ocurre esta secuencia espec\\u00edfica, se produce un segundo desbordamiento insuficiente (pero no se informa): /sys/kernel/debug/tracing # modprobe usb_f_fs /sys/kernel/debug/tracing# echo ffs_data_clear \u0026gt; set_ftrace_filter /sys/kernel/debug/tracing# echo function \u0026gt; current_tracer /sys/kernel/debug/tracing# echo 1 \u0026gt; tracing_on (dispositivo de configuraci\\u00f3n, funci\\u00f3n ejecutar y finalizar proceso de usuario, dispositivo de desmontaje) /sys/kernel/debug/tracing# echo 0 \u0026gt; tracing_on /sys/kernel/debug/tracing# cat trace smartcard-openp-436 [000] ..... 1946.208786: ffs_data_clear \u0026lt;-ffs_data_closed tarjeta inteligente -openp-431 [000] ..... 1946.279147: ffs_data_clear \u0026lt;-ffs_data_closed smartcard-openp-431 [000] .n... 1946.905512: ffs_data_clear \u0026lt;-ffs_data_put Salida de advertencia correspondiente al seguimiento anterior: [ 1946.284139] ADVERTENCIA: CPU : 0 PID: 431 en lib/refcount.c:28 refcount_warn_saturate+0x110/0x15c [ 1946.293094] refcount_t: desbordamiento insuficiente; use-after-free. [1946.298164] M\\u00f3dulos vinculados en: usb_f_ncm(E) u_ether(E) usb_f_fs(E) hci_uart(E) btqca(E) btrtl(E) btbcm(E) btintel(E) bluetooth(E) nls_ascii(E) nls_cp437(E ) vfat(E) fat(E) bcm2835_v4l2(CE) bcm2835_mmal_vchiq(CE) videobuf2_vmalloc(E) videobuf2_memops(E) sha512_generic(E) videobuf2_v4l2(E) sha512_arm(E) videobuf2_common(E) videodev(E) cpufreq_dt(E) snd_b cm2835 (CE) brcmfmac(E) mc(E) vc4(E) ctr(E) brcmutil(E) snd_soc_core(E) snd_pcm_dmaengine(E) drbg(E) snd_pcm(E) snd_timer(E) snd(E) soundcore(E ) drm_kms_helper(E) cec(E) ansi_cprng(E) rc_core(E) syscopyarea(E) raspberrypi_cpufreq(E) sysfillrect(E) sysimgblt(E) cfg80211(E) max17040_battery(OE) raspberrypi_hwmon(E) fb_sys_fops(E) regmap_i2c (E) ecdh_generic(E) rfkill(E) ecc(E) bcm2835_rng(E) rng_core(E) vchiq(CE) leds_gpio(E) libcomposite(E) fuse(E) configfs(E) ip_tables(E) x_tables(E ) autofs4(E) ext4(E) crc16(E) mbcache(E) jbd2(E) crc32c_generic(E) sdhci_iproc(E) sdhci_pltfm(E) sdhci(E) [ 1946.399633] CPU: 0 PID: 431 Comm: tarjeta inteligente- openp Contaminado: GC OE 5.15.0-1-rpi #1 Debian 5.15.3-1 [ 1946.417950] Nombre de hardware: BCM2835 [ 1946.425442] Seguimiento inverso: [ 1946.432048] [] (dump_backtrace) de [] ( show_stack+0x20/0x24) [ 1946.448226] r7:00000009 r6:0000001c r5:c04a948c r4:c0a64e2c [ 1946.458412] [] (show_stack) de [] (dump_ pila+0x28/0x30) [ 1946.470380] [\u0026lt; c08d9ab8\u0026gt;] (dump_stack) de [] (__warn+0xe8/0x154) [ 1946.482067] r5:c04a948c r4:c0a71dc8 [ 1946.490184] [] (__warn) de [] (warn_slowpath_fmt+0xa0/ 0xe4) [ 1946.506758] r7:00000009 r6:0000001c r5:c0a71dc8 r4:c0a71e04 [ 1946.517070] [] (warn_slowpath_fmt) de [] (refcount_war n_saturado+0x110/0x15c) [ 1946.535309] r8:c0100224 r7:c0dfcb84 r6:ffffffff r5:c3b84c00 r4:c24a17c0 [ 1946.546708] [] (refcount_warn_saturate) de [] (eventfd_ctx_put+0x48/0x74) [ 1946.564476] [] (eventfd_ctx_put) de [] (ffs_data_clear+0xd0/0x118 [usb_f_fs]) [ 1946.582664] r5:c3b84c00 r4:c2695b00 [ 1946.590668] [] (ffs_data_clear [usb_f_fs]) de [] ( ffs_data_closed+0x9c/0x150 [usb_f_fs]) [ 1946.609608] r5:bf54d014 r4:c2695b00 [ 1946.617522] [] (ffs_data_closed [usb_f_fs\"}]",
      "id": "CVE-2021-46933",
      "lastModified": "2024-11-21T06:34:57.927",
      "metrics": "{\"cvssMetricV31\": [{\"source\": \"nvd@nist.gov\", \"type\": \"Primary\", \"cvssData\": {\"version\": \"3.1\", \"vectorString\": \"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H\", \"baseScore\": 5.5, \"baseSeverity\": \"MEDIUM\", \"attackVector\": \"LOCAL\", \"attackComplexity\": \"LOW\", \"privilegesRequired\": \"LOW\", \"userInteraction\": \"NONE\", \"scope\": \"UNCHANGED\", \"confidentialityImpact\": \"NONE\", \"integrityImpact\": \"NONE\", \"availabilityImpact\": \"HIGH\"}, \"exploitabilityScore\": 1.8, \"impactScore\": 3.6}]}",
      "published": "2024-02-27T10:15:07.807",
      "references": "[{\"url\": \"https://git.kernel.org/stable/c/1c4ace3e6b8575745c50dca9e76e0021e697d645\", \"source\": \"416baaa9-dc9f-4396-8d5f-8c081fb06d67\", \"tags\": [\"Patch\"]}, {\"url\": \"https://git.kernel.org/stable/c/240fc586e83d645912accce081a48aa63a45f6ee\", \"source\": \"416baaa9-dc9f-4396-8d5f-8c081fb06d67\", \"tags\": [\"Patch\"]}, {\"url\": \"https://git.kernel.org/stable/c/33f6a0cbb7772146e1c11f38028fffbfed14728b\", \"source\": \"416baaa9-dc9f-4396-8d5f-8c081fb06d67\", \"tags\": [\"Patch\"]}, {\"url\": \"https://git.kernel.org/stable/c/52500239e3f2d6fc77b6f58632a9fb98fe74ac09\", \"source\": \"416baaa9-dc9f-4396-8d5f-8c081fb06d67\", \"tags\": [\"Patch\"]}, {\"url\": \"https://git.kernel.org/stable/c/b1e0887379422975f237d43d8839b751a6bcf154\", \"source\": \"416baaa9-dc9f-4396-8d5f-8c081fb06d67\", \"tags\": [\"Patch\"]}, {\"url\": \"https://git.kernel.org/stable/c/cc8c8028c21b2a3842a1e98e99e55028df275919\", \"source\": \"416baaa9-dc9f-4396-8d5f-8c081fb06d67\", \"tags\": [\"Patch\"]}, {\"url\": \"https://git.kernel.org/stable/c/ebef2aa29f370b5096c16020c104e393192ef684\", \"source\": \"416baaa9-dc9f-4396-8d5f-8c081fb06d67\", \"tags\": [\"Patch\"]}, {\"url\": \"https://git.kernel.org/stable/c/f976dd7011150244a7ba820f2c331e9fb253befa\", \"source\": \"416baaa9-dc9f-4396-8d5f-8c081fb06d67\", \"tags\": [\"Patch\"]}, {\"url\": \"https://git.kernel.org/stable/c/1c4ace3e6b8575745c50dca9e76e0021e697d645\", \"source\": \"af854a3a-2127-422b-91ae-364da2661108\", \"tags\": [\"Patch\"]}, {\"url\": \"https://git.kernel.org/stable/c/240fc586e83d645912accce081a48aa63a45f6ee\", \"source\": \"af854a3a-2127-422b-91ae-364da2661108\", \"tags\": [\"Patch\"]}, {\"url\": \"https://git.kernel.org/stable/c/33f6a0cbb7772146e1c11f38028fffbfed14728b\", \"source\": \"af854a3a-2127-422b-91ae-364da2661108\", \"tags\": [\"Patch\"]}, {\"url\": \"https://git.kernel.org/stable/c/52500239e3f2d6fc77b6f58632a9fb98fe74ac09\", \"source\": \"af854a3a-2127-422b-91ae-364da2661108\", \"tags\": [\"Patch\"]}, {\"url\": \"https://git.kernel.org/stable/c/b1e0887379422975f237d43d8839b751a6bcf154\", \"source\": \"af854a3a-2127-422b-91ae-364da2661108\", \"tags\": [\"Patch\"]}, {\"url\": \"https://git.kernel.org/stable/c/cc8c8028c21b2a3842a1e98e99e55028df275919\", \"source\": \"af854a3a-2127-422b-91ae-364da2661108\", \"tags\": [\"Patch\"]}, {\"url\": \"https://git.kernel.org/stable/c/ebef2aa29f370b5096c16020c104e393192ef684\", \"source\": \"af854a3a-2127-422b-91ae-364da2661108\", \"tags\": [\"Patch\"]}, {\"url\": \"https://git.kernel.org/stable/c/f976dd7011150244a7ba820f2c331e9fb253befa\", \"source\": \"af854a3a-2127-422b-91ae-364da2661108\", \"tags\": [\"Patch\"]}]",
      "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "vulnStatus": "Modified",
      "weaknesses": "[{\"source\": \"nvd@nist.gov\", \"type\": \"Primary\", \"description\": [{\"lang\": \"en\", \"value\": \"CWE-416\"}]}]"
    },
    "nvd": "{\"cve\":{\"id\":\"CVE-2021-46933\",\"sourceIdentifier\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\",\"published\":\"2024-02-27T10:15:07.807\",\"lastModified\":\"2026-06-17T04:15:53.880\",\"vulnStatus\":\"Modified\",\"cveTags\":[],\"descriptions\":[{\"lang\":\"en\",\"value\":\"In the Linux kernel, the following vulnerability has been resolved:\\n\\nusb: gadget: f_fs: Clear ffs_eventfd in ffs_data_clear.\\n\\nffs_data_clear is indirectly called from both ffs_fs_kill_sb and\\nffs_ep0_release, so it ends up being called twice when userland closes ep0\\nand then unmounts f_fs.\\nIf userland provided an eventfd along with function\u0027s USB descriptors, it\\nends up calling eventfd_ctx_put as many times, causing a refcount\\nunderflow.\\nNULL-ify ffs_eventfd to prevent these extraneous eventfd_ctx_put calls.\\n\\nAlso, set epfiles to NULL right after de-allocating it, for readability.\\n\\nFor completeness, ffs_data_clear actually ends up being called thrice, the\\nlast call being before the whole ffs structure gets freed, so when this\\nspecific sequence happens there is a second underflow happening (but not\\nbeing reported):\\n\\n/sys/kernel/debug/tracing# modprobe usb_f_fs\\n/sys/kernel/debug/tracing# echo ffs_data_clear \u003e set_ftrace_filter\\n/sys/kernel/debug/tracing# echo function \u003e current_tracer\\n/sys/kernel/debug/tracing# echo 1 \u003e tracing_on\\n(setup gadget, run and kill function userland process, teardown gadget)\\n/sys/kernel/debug/tracing# echo 0 \u003e tracing_on\\n/sys/kernel/debug/tracing# cat trace\\n smartcard-openp-436     [000] .....  1946.208786: ffs_data_clear \u003c-ffs_data_closed\\n smartcard-openp-431     [000] .....  1946.279147: ffs_data_clear \u003c-ffs_data_closed\\n smartcard-openp-431     [000] .n...  1946.905512: ffs_data_clear \u003c-ffs_data_put\\n\\nWarning output corresponding to above trace:\\n[ 1946.284139] WARNING: CPU: 0 PID: 431 at lib/refcount.c:28 refcount_warn_saturate+0x110/0x15c\\n[ 1946.293094] refcount_t: underflow; use-after-free.\\n[ 1946.298164] Modules linked in: usb_f_ncm(E) u_ether(E) usb_f_fs(E) hci_uart(E) btqca(E) btrtl(E) btbcm(E) btintel(E) bluetooth(E) nls_ascii(E) nls_cp437(E) vfat(E) fat(E) bcm2835_v4l2(CE) bcm2835_mmal_vchiq(CE) videobuf2_vmalloc(E) videobuf2_memops(E) sha512_generic(E) videobuf2_v4l2(E) sha512_arm(E) videobuf2_common(E) videodev(E) cpufreq_dt(E) snd_bcm2835(CE) brcmfmac(E) mc(E) vc4(E) ctr(E) brcmutil(E) snd_soc_core(E) snd_pcm_dmaengine(E) drbg(E) snd_pcm(E) snd_timer(E) snd(E) soundcore(E) drm_kms_helper(E) cec(E) ansi_cprng(E) rc_core(E) syscopyarea(E) raspberrypi_cpufreq(E) sysfillrect(E) sysimgblt(E) cfg80211(E) max17040_battery(OE) raspberrypi_hwmon(E) fb_sys_fops(E) regmap_i2c(E) ecdh_generic(E) rfkill(E) ecc(E) bcm2835_rng(E) rng_core(E) vchiq(CE) leds_gpio(E) libcomposite(E) fuse(E) configfs(E) ip_tables(E) x_tables(E) autofs4(E) ext4(E) crc16(E) mbcache(E) jbd2(E) crc32c_generic(E) sdhci_iproc(E) sdhci_pltfm(E) sdhci(E)\\n[ 1946.399633] CPU: 0 PID: 431 Comm: smartcard-openp Tainted: G         C OE     5.15.0-1-rpi #1  Debian 5.15.3-1\\n[ 1946.417950] Hardware name: BCM2835\\n[ 1946.425442] Backtrace:\\n[ 1946.432048] [\u003cc08d60a0\u003e] (dump_backtrace) from [\u003cc08d62ec\u003e] (show_stack+0x20/0x24)\\n[ 1946.448226]  r7:00000009 r6:0000001c r5:c04a948c r4:c0a64e2c\\n[ 1946.458412] [\u003cc08d62cc\u003e] (show_stack) from [\u003cc08d9ae0\u003e] (dump_stack+0x28/0x30)\\n[ 1946.470380] [\u003cc08d9ab8\u003e] (dump_stack) from [\u003cc0123500\u003e] (__warn+0xe8/0x154)\\n[ 1946.482067]  r5:c04a948c r4:c0a71dc8\\n[ 1946.490184] [\u003cc0123418\u003e] (__warn) from [\u003cc08d6948\u003e] (warn_slowpath_fmt+0xa0/0xe4)\\n[ 1946.506758]  r7:00000009 r6:0000001c r5:c0a71dc8 r4:c0a71e04\\n[ 1946.517070] [\u003cc08d68ac\u003e] (warn_slowpath_fmt) from [\u003cc04a948c\u003e] (refcount_warn_saturate+0x110/0x15c)\\n[ 1946.535309]  r8:c0100224 r7:c0dfcb84 r6:ffffffff r5:c3b84c00 r4:c24a17c0\\n[ 1946.546708] [\u003cc04a937c\u003e] (refcount_warn_saturate) from [\u003cc0380134\u003e] (eventfd_ctx_put+0x48/0x74)\\n[ 1946.564476] [\u003cc03800ec\u003e] (eventfd_ctx_put) from [\u003cbf5464e8\u003e] (ffs_data_clear+0xd0/0x118 [usb_f_fs])\\n[ 1946.582664]  r5:c3b84c00 r4:c2695b00\\n[ 1946.590668] [\u003cbf546418\u003e] (ffs_data_clear [usb_f_fs]) from [\u003cbf547cc0\u003e] (ffs_data_closed+0x9c/0x150 [usb_f_fs])\\n[ 1946.609608]  r5:bf54d014 r4:c2695b00\\n[ 1946.617522] [\u003cbf547c24\u003e] (ffs_data_closed [usb_f_fs]) from [\u003cbf547da0\u003e] (ffs_fs_kill_sb+0x2c/0x30 [usb_f_fs])\\n[ 1946.636217]  r7:c0dfcb\\n---truncated---\"},{\"lang\":\"es\",\"value\":\"En el kernel de Linux se ha resuelto la siguiente vulnerabilidad: usb: gadget: f_fs: Borrar ffs_eventfd en ffs_data_clear. ffs_data_clear se llama indirectamente desde ffs_fs_kill_sb y ffs_ep0_release, por lo que termina siendo llamado dos veces cuando el \u00e1rea de usuario cierra ep0 y luego desmonta f_fs. Si Userland proporcion\u00f3 un eventfd junto con los descriptores USB de la funci\u00f3n, termina llamando a eventfd_ctx_put tantas veces, provocando un desbordamiento insuficiente de recuento. NULL-ify ffs_eventfd para evitar estas llamadas extra\u00f1as eventfd_ctx_put. Adem\u00e1s, establezca epfiles en NULL justo despu\u00e9s de desasignarlo, para facilitar la lectura. Para completar, ffs_data_clear en realidad termina siendo llamado tres veces, la \u00faltima llamada es antes de que se libere toda la estructura de ffs, por lo que cuando ocurre esta secuencia espec\u00edfica, se produce un segundo desbordamiento insuficiente (pero no se informa): /sys/kernel/debug/tracing # modprobe usb_f_fs /sys/kernel/debug/tracing# echo ffs_data_clear \u0026gt; set_ftrace_filter /sys/kernel/debug/tracing# echo function \u0026gt; current_tracer /sys/kernel/debug/tracing# echo 1 \u0026gt; tracing_on (dispositivo de configuraci\u00f3n, funci\u00f3n ejecutar y finalizar proceso de usuario, dispositivo de desmontaje) /sys/kernel/debug/tracing# echo 0 \u0026gt; tracing_on /sys/kernel/debug/tracing# cat trace smartcard-openp-436 [000] ..... 1946.208786: ffs_data_clear \u0026lt;-ffs_data_closed tarjeta inteligente -openp-431 [000] ..... 1946.279147: ffs_data_clear \u0026lt;-ffs_data_closed smartcard-openp-431 [000] .n... 1946.905512: ffs_data_clear \u0026lt;-ffs_data_put Salida de advertencia correspondiente al seguimiento anterior: [ 1946.284139] ADVERTENCIA: CPU : 0 PID: 431 en lib/refcount.c:28 refcount_warn_saturate+0x110/0x15c [ 1946.293094] refcount_t: desbordamiento insuficiente; use-after-free. [1946.298164] M\u00f3dulos vinculados en: usb_f_ncm(E) u_ether(E) usb_f_fs(E) hci_uart(E) btqca(E) btrtl(E) btbcm(E) btintel(E) bluetooth(E) nls_ascii(E) nls_cp437(E ) vfat(E) fat(E) bcm2835_v4l2(CE) bcm2835_mmal_vchiq(CE) videobuf2_vmalloc(E) videobuf2_memops(E) sha512_generic(E) videobuf2_v4l2(E) sha512_arm(E) videobuf2_common(E) videodev(E) cpufreq_dt(E) snd_b cm2835 (CE) brcmfmac(E) mc(E) vc4(E) ctr(E) brcmutil(E) snd_soc_core(E) snd_pcm_dmaengine(E) drbg(E) snd_pcm(E) snd_timer(E) snd(E) soundcore(E ) drm_kms_helper(E) cec(E) ansi_cprng(E) rc_core(E) syscopyarea(E) raspberrypi_cpufreq(E) sysfillrect(E) sysimgblt(E) cfg80211(E) max17040_battery(OE) raspberrypi_hwmon(E) fb_sys_fops(E) regmap_i2c (E) ecdh_generic(E) rfkill(E) ecc(E) bcm2835_rng(E) rng_core(E) vchiq(CE) leds_gpio(E) libcomposite(E) fuse(E) configfs(E) ip_tables(E) x_tables(E ) autofs4(E) ext4(E) crc16(E) mbcache(E) jbd2(E) crc32c_generic(E) sdhci_iproc(E) sdhci_pltfm(E) sdhci(E) [ 1946.399633] CPU: 0 PID: 431 Comm: tarjeta inteligente- openp Contaminado: GC OE 5.15.0-1-rpi #1 Debian 5.15.3-1 [ 1946.417950] Nombre de hardware: BCM2835 [ 1946.425442] Seguimiento inverso: [ 1946.432048] [] (dump_backtrace) de [] ( show_stack+0x20/0x24) [ 1946.448226] r7:00000009 r6:0000001c r5:c04a948c r4:c0a64e2c [ 1946.458412] [] (show_stack) de [] (dump_ pila+0x28/0x30) [ 1946.470380] [\u0026lt; c08d9ab8\u0026gt;] (dump_stack) de [] (__warn+0xe8/0x154) [ 1946.482067] r5:c04a948c r4:c0a71dc8 [ 1946.490184] [] (__warn) de [] (warn_slowpath_fmt+0xa0/ 0xe4) [ 1946.506758] r7:00000009 r6:0000001c r5:c0a71dc8 r4:c0a71e04 [ 1946.517070] [] (warn_slowpath_fmt) de [] (refcount_war n_saturado+0x110/0x15c) [ 1946.535309] r8:c0100224 r7:c0dfcb84 r6:ffffffff r5:c3b84c00 r4:c24a17c0 [ 1946.546708] [] (refcount_warn_saturate) de [] (eventfd_ctx_put+0x48/0x74) [ 1946.564476] [] (eventfd_ctx_put) de [] (ffs_data_clear+0xd0/0x118 [usb_f_fs]) [ 1946.582664] r5:c3b84c00 r4:c2695b00 [ 1946.590668] [] (ffs_data_clear [usb_f_fs]) de [] ( ffs_data_closed+0x9c/0x150 [usb_f_fs]) [ 1946.609608] r5:bf54d014 r4:c2695b00 [ 1946.617522] [] (ffs_data_closed [usb_f_fs\"}],\"affected\":[{\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\",\"affectedData\":[{\"vendor\":\"Linux\",\"product\":\"Linux\",\"defaultStatus\":\"unaffected\",\"programFiles\":[\"drivers/usb/gadget/function/f_fs.c\"],\"repo\":\"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git\",\"versions\":[{\"version\":\"5e33f6fdf735cda1d4580fe6f1878da05718fe73\",\"lessThan\":\"f976dd7011150244a7ba820f2c331e9fb253befa\",\"versionType\":\"git\",\"status\":\"affected\"},{\"version\":\"5e33f6fdf735cda1d4580fe6f1878da05718fe73\",\"lessThan\":\"cc8c8028c21b2a3842a1e98e99e55028df275919\",\"versionType\":\"git\",\"status\":\"affected\"},{\"version\":\"5e33f6fdf735cda1d4580fe6f1878da05718fe73\",\"lessThan\":\"52500239e3f2d6fc77b6f58632a9fb98fe74ac09\",\"versionType\":\"git\",\"status\":\"affected\"},{\"version\":\"5e33f6fdf735cda1d4580fe6f1878da05718fe73\",\"lessThan\":\"33f6a0cbb7772146e1c11f38028fffbfed14728b\",\"versionType\":\"git\",\"status\":\"affected\"},{\"version\":\"5e33f6fdf735cda1d4580fe6f1878da05718fe73\",\"lessThan\":\"240fc586e83d645912accce081a48aa63a45f6ee\",\"versionType\":\"git\",\"status\":\"affected\"},{\"version\":\"5e33f6fdf735cda1d4580fe6f1878da05718fe73\",\"lessThan\":\"1c4ace3e6b8575745c50dca9e76e0021e697d645\",\"versionType\":\"git\",\"status\":\"affected\"},{\"version\":\"5e33f6fdf735cda1d4580fe6f1878da05718fe73\",\"lessThan\":\"ebef2aa29f370b5096c16020c104e393192ef684\",\"versionType\":\"git\",\"status\":\"affected\"},{\"version\":\"5e33f6fdf735cda1d4580fe6f1878da05718fe73\",\"lessThan\":\"b1e0887379422975f237d43d8839b751a6bcf154\",\"versionType\":\"git\",\"status\":\"affected\"}]},{\"vendor\":\"Linux\",\"product\":\"Linux\",\"defaultStatus\":\"affected\",\"programFiles\":[\"drivers/usb/gadget/function/f_fs.c\"],\"repo\":\"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git\",\"versions\":[{\"version\":\"4.0\",\"status\":\"affected\"},{\"version\":\"0\",\"lessThan\":\"4.0\",\"versionType\":\"semver\",\"status\":\"unaffected\"},{\"version\":\"4.4.298\",\"lessThanOrEqual\":\"4.4.*\",\"versionType\":\"semver\",\"status\":\"unaffected\"},{\"version\":\"4.9.296\",\"lessThanOrEqual\":\"4.9.*\",\"versionType\":\"semver\",\"status\":\"unaffected\"},{\"version\":\"4.14.261\",\"lessThanOrEqual\":\"4.14.*\",\"versionType\":\"semver\",\"status\":\"unaffected\"},{\"version\":\"4.19.224\",\"lessThanOrEqual\":\"4.19.*\",\"versionType\":\"semver\",\"status\":\"unaffected\"},{\"version\":\"5.4.170\",\"lessThanOrEqual\":\"5.4.*\",\"versionType\":\"semver\",\"status\":\"unaffected\"},{\"version\":\"5.10.90\",\"lessThanOrEqual\":\"5.10.*\",\"versionType\":\"semver\",\"status\":\"unaffected\"},{\"version\":\"5.15.13\",\"lessThanOrEqual\":\"5.15.*\",\"versionType\":\"semver\",\"status\":\"unaffected\"},{\"version\":\"5.16\",\"lessThanOrEqual\":\"*\",\"versionType\":\"original_commit_for_fix\",\"status\":\"unaffected\"}]}]}],\"metrics\":{\"cvssMetricV31\":[{\"source\":\"nvd@nist.gov\",\"type\":\"Primary\",\"cvssData\":{\"version\":\"3.1\",\"vectorString\":\"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H\",\"baseScore\":5.5,\"baseSeverity\":\"MEDIUM\",\"attackVector\":\"LOCAL\",\"attackComplexity\":\"LOW\",\"privilegesRequired\":\"LOW\",\"userInteraction\":\"NONE\",\"scope\":\"UNCHANGED\",\"confidentialityImpact\":\"NONE\",\"integrityImpact\":\"NONE\",\"availabilityImpact\":\"HIGH\"},\"exploitabilityScore\":1.8,\"impactScore\":3.6},{\"source\":\"134c704f-9b21-4f2e-91b3-4a467353bcc0\",\"type\":\"Secondary\",\"cvssData\":{\"version\":\"3.1\",\"vectorString\":\"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H\",\"baseScore\":5.5,\"baseSeverity\":\"MEDIUM\",\"attackVector\":\"LOCAL\",\"attackComplexity\":\"LOW\",\"privilegesRequired\":\"LOW\",\"userInteraction\":\"NONE\",\"scope\":\"UNCHANGED\",\"confidentialityImpact\":\"NONE\",\"integrityImpact\":\"NONE\",\"availabilityImpact\":\"HIGH\"},\"exploitabilityScore\":1.8,\"impactScore\":3.6}],\"ssvcV203\":[{\"source\":\"134c704f-9b21-4f2e-91b3-4a467353bcc0\",\"ssvcData\":{\"timestamp\":\"2025-04-22T16:12:25.365291Z\",\"id\":\"CVE-2021-46933\",\"options\":[{\"exploitation\":\"none\"},{\"automatable\":\"no\"},{\"technicalImpact\":\"partial\"}],\"role\":\"CISA Coordinator\",\"version\":\"2.0.3\"}}]},\"weaknesses\":[{\"source\":\"nvd@nist.gov\",\"type\":\"Primary\",\"description\":[{\"lang\":\"en\",\"value\":\"CWE-416\"}]},{\"source\":\"134c704f-9b21-4f2e-91b3-4a467353bcc0\",\"type\":\"Secondary\",\"description\":[{\"lang\":\"en\",\"value\":\"CWE-476\"}]}],\"configurations\":[{\"nodes\":[{\"operator\":\"OR\",\"negate\":false,\"cpeMatch\":[{\"vulnerable\":true,\"criteria\":\"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\",\"versionStartIncluding\":\"4.0.0\",\"versionEndExcluding\":\"4.4.298\",\"matchCriteriaId\":\"C01E3FB6-531E-4ABC-BF95-6FADD48AE7E0\"},{\"vulnerable\":true,\"criteria\":\"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\",\"versionStartIncluding\":\"4.5.0\",\"versionEndExcluding\":\"4.9.296\",\"matchCriteriaId\":\"883CB22B-11DA-4D54-8121-3F5494EDBD4C\"},{\"vulnerable\":true,\"criteria\":\"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\",\"versionStartIncluding\":\"4.10.0\",\"versionEndExcluding\":\"4.14.261\",\"matchCriteriaId\":\"B5D4F856-5F69-4F4A-911F-50A21B9A68B6\"},{\"vulnerable\":true,\"criteria\":\"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\",\"versionStartIncluding\":\"4.15.0\",\"versionEndExcluding\":\"4.19.224\",\"matchCriteriaId\":\"B34A1353-506A-4AB9-87EC-CD50F09DFB8A\"},{\"vulnerable\":true,\"criteria\":\"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\",\"versionStartIncluding\":\"4.20.0\",\"versionEndExcluding\":\"5.4.170\",\"matchCriteriaId\":\"56D16FBB-453E-4316-A027-E517828203D7\"},{\"vulnerable\":true,\"criteria\":\"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\",\"versionStartIncluding\":\"5.5.0\",\"versionEndExcluding\":\"5.10.90\",\"matchCriteriaId\":\"C87FB3FD-3E74-4588-A1A4-B9BA8AE0C06B\"},{\"vulnerable\":true,\"criteria\":\"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\",\"versionStartIncluding\":\"5.11.0\",\"versionEndExcluding\":\"5.15.13\",\"matchCriteriaId\":\"083E0940-932B-447B-A6B2-677DAE27FD04\"}]}]}],\"references\":[{\"url\":\"https://git.kernel.org/stable/c/1c4ace3e6b8575745c50dca9e76e0021e697d645\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\",\"tags\":[\"Patch\"]},{\"url\":\"https://git.kernel.org/stable/c/240fc586e83d645912accce081a48aa63a45f6ee\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\",\"tags\":[\"Patch\"]},{\"url\":\"https://git.kernel.org/stable/c/33f6a0cbb7772146e1c11f38028fffbfed14728b\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\",\"tags\":[\"Patch\"]},{\"url\":\"https://git.kernel.org/stable/c/52500239e3f2d6fc77b6f58632a9fb98fe74ac09\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\",\"tags\":[\"Patch\"]},{\"url\":\"https://git.kernel.org/stable/c/b1e0887379422975f237d43d8839b751a6bcf154\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\",\"tags\":[\"Patch\"]},{\"url\":\"https://git.kernel.org/stable/c/cc8c8028c21b2a3842a1e98e99e55028df275919\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\",\"tags\":[\"Patch\"]},{\"url\":\"https://git.kernel.org/stable/c/ebef2aa29f370b5096c16020c104e393192ef684\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\",\"tags\":[\"Patch\"]},{\"url\":\"https://git.kernel.org/stable/c/f976dd7011150244a7ba820f2c331e9fb253befa\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\",\"tags\":[\"Patch\"]},{\"url\":\"https://git.kernel.org/stable/c/1c4ace3e6b8575745c50dca9e76e0021e697d645\",\"source\":\"af854a3a-2127-422b-91ae-364da2661108\",\"tags\":[\"Patch\"]},{\"url\":\"https://git.kernel.org/stable/c/240fc586e83d645912accce081a48aa63a45f6ee\",\"source\":\"af854a3a-2127-422b-91ae-364da2661108\",\"tags\":[\"Patch\"]},{\"url\":\"https://git.kernel.org/stable/c/33f6a0cbb7772146e1c11f38028fffbfed14728b\",\"source\":\"af854a3a-2127-422b-91ae-364da2661108\",\"tags\":[\"Patch\"]},{\"url\":\"https://git.kernel.org/stable/c/52500239e3f2d6fc77b6f58632a9fb98fe74ac09\",\"source\":\"af854a3a-2127-422b-91ae-364da2661108\",\"tags\":[\"Patch\"]},{\"url\":\"https://git.kernel.org/stable/c/b1e0887379422975f237d43d8839b751a6bcf154\",\"source\":\"af854a3a-2127-422b-91ae-364da2661108\",\"tags\":[\"Patch\"]},{\"url\":\"https://git.kernel.org/stable/c/cc8c8028c21b2a3842a1e98e99e55028df275919\",\"source\":\"af854a3a-2127-422b-91ae-364da2661108\",\"tags\":[\"Patch\"]},{\"url\":\"https://git.kernel.org/stable/c/ebef2aa29f370b5096c16020c104e393192ef684\",\"source\":\"af854a3a-2127-422b-91ae-364da2661108\",\"tags\":[\"Patch\"]},{\"url\":\"https://git.kernel.org/stable/c/f976dd7011150244a7ba820f2c331e9fb253befa\",\"source\":\"af854a3a-2127-422b-91ae-364da2661108\",\"tags\":[\"Patch\"]}]}}",
    "redhat_vex": {
      "aggregate_severity": "Low",
      "current_release_date": "2025-11-21T11:53:19+00:00",
      "cve": "CVE-2021-46933",
      "id": "CVE-2021-46933",
      "initial_release_date": "2021-01-01T00:00:00+00:00",
      "product_status:known_affected": "42",
      "product_status:known_not_affected": "156",
      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "kernel: usb: gadget: f_fs: Clear ffs_eventfd in ffs_data_clear.",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2021/cve-2021-46933.json",
      "version": "3"
    },
    "suse_vex": {
      "aggregate_severity": "moderate",
      "current_release_date": "2026-06-06T06:09:25Z",
      "cve": "CVE-2021-46933",
      "id": "CVE-2021-46933",
      "initial_release_date": "2024-02-28T04:02:17Z",
      "product_status:known_affected": "254",
      "product_status:known_not_affected": "127",
      "product_status:recommended": "606",
      "source": "SUSE CSAF VEX",
      "status": "interim",
      "title": "SUSE CVE CVE-2021-46933",
      "url": "https://ftp.suse.com/pub/projects/security/csaf-vex/cve-2021-46933.json",
      "version": "55"
    },
    "vulnrichment": {
      "containers": "{\"adp\": [{\"title\": \"CVE Program Container\", \"references\": [{\"url\": \"https://git.kernel.org/stable/c/f976dd7011150244a7ba820f2c331e9fb253befa\", \"tags\": [\"x_transferred\"]}, {\"url\": \"https://git.kernel.org/stable/c/cc8c8028c21b2a3842a1e98e99e55028df275919\", \"tags\": [\"x_transferred\"]}, {\"url\": \"https://git.kernel.org/stable/c/52500239e3f2d6fc77b6f58632a9fb98fe74ac09\", \"tags\": [\"x_transferred\"]}, {\"url\": \"https://git.kernel.org/stable/c/33f6a0cbb7772146e1c11f38028fffbfed14728b\", \"tags\": [\"x_transferred\"]}, {\"url\": \"https://git.kernel.org/stable/c/240fc586e83d645912accce081a48aa63a45f6ee\", \"tags\": [\"x_transferred\"]}, {\"url\": \"https://git.kernel.org/stable/c/1c4ace3e6b8575745c50dca9e76e0021e697d645\", \"tags\": [\"x_transferred\"]}, {\"url\": \"https://git.kernel.org/stable/c/ebef2aa29f370b5096c16020c104e393192ef684\", \"tags\": [\"x_transferred\"]}, {\"url\": \"https://git.kernel.org/stable/c/b1e0887379422975f237d43d8839b751a6bcf154\", \"tags\": [\"x_transferred\"]}], \"providerMetadata\": {\"orgId\": \"af854a3a-2127-422b-91ae-364da2661108\", \"shortName\": \"CVE\", \"dateUpdated\": \"2024-08-04T05:17:43.071Z\"}}, {\"title\": \"CISA ADP Vulnrichment\", \"metrics\": [{\"cvssV3_1\": {\"scope\": \"UNCHANGED\", \"version\": \"3.1\", \"baseScore\": 5.5, \"attackVector\": \"LOCAL\", \"baseSeverity\": \"MEDIUM\", \"vectorString\": \"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H\", \"integrityImpact\": \"NONE\", \"userInteraction\": \"NONE\", \"attackComplexity\": \"LOW\", \"availabilityImpact\": \"HIGH\", \"privilegesRequired\": \"LOW\", \"confidentialityImpact\": \"NONE\"}}, {\"other\": {\"type\": \"ssvc\", \"content\": {\"id\": \"CVE-2021-46933\", \"role\": \"CISA Coordinator\", \"options\": [{\"Exploitation\": \"none\"}, {\"Automatable\": \"no\"}, {\"Technical Impact\": \"partial\"}], \"version\": \"2.0.3\", \"timestamp\": \"2025-04-22T16:12:25.365291Z\"}}}], \"problemTypes\": [{\"descriptions\": [{\"lang\": \"en\", \"type\": \"CWE\", \"cweId\": \"CWE-476\", \"description\": \"CWE-476 NULL Pointer Dereference\"}]}], \"providerMetadata\": {\"orgId\": \"134c704f-9b21-4f2e-91b3-4a467353bcc0\", \"shortName\": \"CISA-ADP\", \"dateUpdated\": \"2024-07-05T15:20:37.728Z\"}}], \"cna\": {\"title\": \"usb: gadget: f_fs: Clear ffs_eventfd in ffs_data_clear.\", \"affected\": [{\"repo\": \"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git\", \"vendor\": \"Linux\", \"product\": \"Linux\", \"versions\": [{\"status\": \"affected\", \"version\": \"5e33f6fdf735cda1d4580fe6f1878da05718fe73\", \"lessThan\": \"f976dd7011150244a7ba820f2c331e9fb253befa\", \"versionType\": \"git\"}, {\"status\": \"affected\", \"version\": \"5e33f6fdf735cda1d4580fe6f1878da05718fe73\", \"lessThan\": \"cc8c8028c21b2a3842a1e98e99e55028df275919\", \"versionType\": \"git\"}, {\"status\": \"affected\", \"version\": \"5e33f6fdf735cda1d4580fe6f1878da05718fe73\", \"lessThan\": \"52500239e3f2d6fc77b6f58632a9fb98fe74ac09\", \"versionType\": \"git\"}, {\"status\": \"affected\", \"version\": \"5e33f6fdf735cda1d4580fe6f1878da05718fe73\", \"lessThan\": \"33f6a0cbb7772146e1c11f38028fffbfed14728b\", \"versionType\": \"git\"}, {\"status\": \"affected\", \"version\": \"5e33f6fdf735cda1d4580fe6f1878da05718fe73\", \"lessThan\": \"240fc586e83d645912accce081a48aa63a45f6ee\", \"versionType\": \"git\"}, {\"status\": \"affected\", \"version\": \"5e33f6fdf735cda1d4580fe6f1878da05718fe73\", \"lessThan\": \"1c4ace3e6b8575745c50dca9e76e0021e697d645\", \"versionType\": \"git\"}, {\"status\": \"affected\", \"version\": \"5e33f6fdf735cda1d4580fe6f1878da05718fe73\", \"lessThan\": \"ebef2aa29f370b5096c16020c104e393192ef684\", \"versionType\": \"git\"}, {\"status\": \"affected\", \"version\": \"5e33f6fdf735cda1d4580fe6f1878da05718fe73\", \"lessThan\": \"b1e0887379422975f237d43d8839b751a6bcf154\", \"versionType\": \"git\"}], \"programFiles\": [\"drivers/usb/gadget/function/f_fs.c\"], \"defaultStatus\": \"unaffected\"}, {\"repo\": \"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git\", \"vendor\": \"Linux\", \"product\": \"Linux\", \"versions\": [{\"status\": \"affected\", \"version\": \"4.0\"}, {\"status\": \"unaffected\", \"version\": \"0\", \"lessThan\": \"4.0\", \"versionType\": \"semver\"}, {\"status\": \"unaffected\", \"version\": \"4.4.298\", \"versionType\": \"semver\", \"lessThanOrEqual\": \"4.4.*\"}, {\"status\": \"unaffected\", \"version\": \"4.9.296\", \"versionType\": \"semver\", \"lessThanOrEqual\": \"4.9.*\"}, {\"status\": \"unaffected\", \"version\": \"4.14.261\", \"versionType\": \"semver\", \"lessThanOrEqual\": \"4.14.*\"}, {\"status\": \"unaffected\", \"version\": \"4.19.224\", \"versionType\": \"semver\", \"lessThanOrEqual\": \"4.19.*\"}, {\"status\": \"unaffected\", \"version\": \"5.4.170\", \"versionType\": \"semver\", \"lessThanOrEqual\": \"5.4.*\"}, {\"status\": \"unaffected\", \"version\": \"5.10.90\", \"versionType\": \"semver\", \"lessThanOrEqual\": \"5.10.*\"}, {\"status\": \"unaffected\", \"version\": \"5.15.13\", \"versionType\": \"semver\", \"lessThanOrEqual\": \"5.15.*\"}, {\"status\": \"unaffected\", \"version\": \"5.16\", \"versionType\": \"original_commit_for_fix\", \"lessThanOrEqual\": \"*\"}], \"programFiles\": [\"drivers/usb/gadget/function/f_fs.c\"], \"defaultStatus\": \"affected\"}], \"references\": [{\"url\": \"https://git.kernel.org/stable/c/f976dd7011150244a7ba820f2c331e9fb253befa\"}, {\"url\": \"https://git.kernel.org/stable/c/cc8c8028c21b2a3842a1e98e99e55028df275919\"}, {\"url\": \"https://git.kernel.org/stable/c/52500239e3f2d6fc77b6f58632a9fb98fe74ac09\"}, {\"url\": \"https://git.kernel.org/stable/c/33f6a0cbb7772146e1c11f38028fffbfed14728b\"}, {\"url\": \"https://git.kernel.org/stable/c/240fc586e83d645912accce081a48aa63a45f6ee\"}, {\"url\": \"https://git.kernel.org/stable/c/1c4ace3e6b8575745c50dca9e76e0021e697d645\"}, {\"url\": \"https://git.kernel.org/stable/c/ebef2aa29f370b5096c16020c104e393192ef684\"}, {\"url\": \"https://git.kernel.org/stable/c/b1e0887379422975f237d43d8839b751a6bcf154\"}], \"x_generator\": {\"engine\": \"bippy-1.2.0\"}, \"descriptions\": [{\"lang\": \"en\", \"value\": \"In the Linux kernel, the following vulnerability has been resolved:\\n\\nusb: gadget: f_fs: Clear ffs_eventfd in ffs_data_clear.\\n\\nffs_data_clear is indirectly called from both ffs_fs_kill_sb and\\nffs_ep0_release, so it ends up being called twice when userland closes ep0\\nand then unmounts f_fs.\\nIf userland provided an eventfd along with function\u0027s USB descriptors, it\\nends up calling eventfd_ctx_put as many times, causing a refcount\\nunderflow.\\nNULL-ify ffs_eventfd to prevent these extraneous eventfd_ctx_put calls.\\n\\nAlso, set epfiles to NULL right after de-allocating it, for readability.\\n\\nFor completeness, ffs_data_clear actually ends up being called thrice, the\\nlast call being before the whole ffs structure gets freed, so when this\\nspecific sequence happens there is a second underflow happening (but not\\nbeing reported):\\n\\n/sys/kernel/debug/tracing# modprobe usb_f_fs\\n/sys/kernel/debug/tracing# echo ffs_data_clear \u003e set_ftrace_filter\\n/sys/kernel/debug/tracing# echo function \u003e current_tracer\\n/sys/kernel/debug/tracing# echo 1 \u003e tracing_on\\n(setup gadget, run and kill function userland process, teardown gadget)\\n/sys/kernel/debug/tracing# echo 0 \u003e tracing_on\\n/sys/kernel/debug/tracing# cat trace\\n smartcard-openp-436     [000] .....  1946.208786: ffs_data_clear \u003c-ffs_data_closed\\n smartcard-openp-431     [000] .....  1946.279147: ffs_data_clear \u003c-ffs_data_closed\\n smartcard-openp-431     [000] .n...  1946.905512: ffs_data_clear \u003c-ffs_data_put\\n\\nWarning output corresponding to above trace:\\n[ 1946.284139] WARNING: CPU: 0 PID: 431 at lib/refcount.c:28 refcount_warn_saturate+0x110/0x15c\\n[ 1946.293094] refcount_t: underflow; use-after-free.\\n[ 1946.298164] Modules linked in: usb_f_ncm(E) u_ether(E) usb_f_fs(E) hci_uart(E) btqca(E) btrtl(E) btbcm(E) btintel(E) bluetooth(E) nls_ascii(E) nls_cp437(E) vfat(E) fat(E) bcm2835_v4l2(CE) bcm2835_mmal_vchiq(CE) videobuf2_vmalloc(E) videobuf2_memops(E) sha512_generic(E) videobuf2_v4l2(E) sha512_arm(E) videobuf2_common(E) videodev(E) cpufreq_dt(E) snd_bcm2835(CE) brcmfmac(E) mc(E) vc4(E) ctr(E) brcmutil(E) snd_soc_core(E) snd_pcm_dmaengine(E) drbg(E) snd_pcm(E) snd_timer(E) snd(E) soundcore(E) drm_kms_helper(E) cec(E) ansi_cprng(E) rc_core(E) syscopyarea(E) raspberrypi_cpufreq(E) sysfillrect(E) sysimgblt(E) cfg80211(E) max17040_battery(OE) raspberrypi_hwmon(E) fb_sys_fops(E) regmap_i2c(E) ecdh_generic(E) rfkill(E) ecc(E) bcm2835_rng(E) rng_core(E) vchiq(CE) leds_gpio(E) libcomposite(E) fuse(E) configfs(E) ip_tables(E) x_tables(E) autofs4(E) ext4(E) crc16(E) mbcache(E) jbd2(E) crc32c_generic(E) sdhci_iproc(E) sdhci_pltfm(E) sdhci(E)\\n[ 1946.399633] CPU: 0 PID: 431 Comm: smartcard-openp Tainted: G         C OE     5.15.0-1-rpi #1  Debian 5.15.3-1\\n[ 1946.417950] Hardware name: BCM2835\\n[ 1946.425442] Backtrace:\\n[ 1946.432048] [\u003cc08d60a0\u003e] (dump_backtrace) from [\u003cc08d62ec\u003e] (show_stack+0x20/0x24)\\n[ 1946.448226]  r7:00000009 r6:0000001c r5:c04a948c r4:c0a64e2c\\n[ 1946.458412] [\u003cc08d62cc\u003e] (show_stack) from [\u003cc08d9ae0\u003e] (dump_stack+0x28/0x30)\\n[ 1946.470380] [\u003cc08d9ab8\u003e] (dump_stack) from [\u003cc0123500\u003e] (__warn+0xe8/0x154)\\n[ 1946.482067]  r5:c04a948c r4:c0a71dc8\\n[ 1946.490184] [\u003cc0123418\u003e] (__warn) from [\u003cc08d6948\u003e] (warn_slowpath_fmt+0xa0/0xe4)\\n[ 1946.506758]  r7:00000009 r6:0000001c r5:c0a71dc8 r4:c0a71e04\\n[ 1946.517070] [\u003cc08d68ac\u003e] (warn_slowpath_fmt) from [\u003cc04a948c\u003e] (refcount_warn_saturate+0x110/0x15c)\\n[ 1946.535309]  r8:c0100224 r7:c0dfcb84 r6:ffffffff r5:c3b84c00 r4:c24a17c0\\n[ 1946.546708] [\u003cc04a937c\u003e] (refcount_warn_saturate) from [\u003cc0380134\u003e] (eventfd_ctx_put+0x48/0x74)\\n[ 1946.564476] [\u003cc03800ec\u003e] (eventfd_ctx_put) from [\u003cbf5464e8\u003e] (ffs_data_clear+0xd0/0x118 [usb_f_fs])\\n[ 1946.582664]  r5:c3b84c00 r4:c2695b00\\n[ 1946.590668] [\u003cbf546418\u003e] (ffs_data_clear [usb_f_fs]) from [\u003cbf547cc0\u003e] (ffs_data_closed+0x9c/0x150 [usb_f_fs])\\n[ 1946.609608]  r5:bf54d014 r4:c2695b00\\n[ 1946.617522] [\u003cbf547c24\u003e] (ffs_data_closed [usb_f_fs]) from [\u003cbf547da0\u003e] (ffs_fs_kill_sb+0x2c/0x30 [usb_f_fs])\\n[ 1946.636217]  r7:c0dfcb\\n---truncated---\"}], \"cpeApplicability\": [{\"nodes\": [{\"negate\": false, \"cpeMatch\": [{\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"4.4.298\", \"versionStartIncluding\": \"4.0\"}, {\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"4.9.296\", \"versionStartIncluding\": \"4.0\"}, {\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"4.14.261\", \"versionStartIncluding\": \"4.0\"}, {\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"4.19.224\", \"versionStartIncluding\": \"4.0\"}, {\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"5.4.170\", \"versionStartIncluding\": \"4.0\"}, {\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"5.10.90\", \"versionStartIncluding\": \"4.0\"}, {\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"5.15.13\", \"versionStartIncluding\": \"4.0\"}, {\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"5.16\", \"versionStartIncluding\": \"4.0\"}], \"operator\": \"OR\"}]}], \"providerMetadata\": {\"orgId\": \"416baaa9-dc9f-4396-8d5f-8c081fb06d67\", \"shortName\": \"Linux\", \"dateUpdated\": \"2026-05-11T13:44:42.774Z\"}}}",
      "cveMetadata": "{\"cveId\": \"CVE-2021-46933\", \"state\": \"PUBLISHED\", \"dateUpdated\": \"2026-05-11T13:44:42.774Z\", \"dateReserved\": \"2024-02-25T13:45:52.720Z\", \"assignerOrgId\": \"416baaa9-dc9f-4396-8d5f-8c081fb06d67\", \"datePublished\": \"2024-02-27T09:44:00.758Z\", \"assignerShortName\": \"Linux\"}",
      "dataType": "CVE_RECORD",
      "dataVersion": "5.2"
    }
  }
}



Log in or create an account to share your comment.




Tags
Taxonomy of the tags.





Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.

Sightings

Author Source Type Date Other

Nomenclature

  • Seen: The vulnerability was mentioned, discussed, or observed by the user.
  • Confirmed: The vulnerability has been validated from an analyst's perspective.
  • Published Proof of Concept: A public proof of concept is available for this vulnerability.
  • Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
  • Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
  • Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
  • Not confirmed: The user expressed doubt about the validity of the vulnerability.
  • Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.


Detection rules are retrieved from Rulezet.