CVE-2021-47383 (GCVE-0-2021-47383)

Vulnerability from cvelistv5 – Published: 2024-05-21 15:03 – Updated: 2026-08-05 08:47
VLAI
Title
tty: Fix out-of-bound vmalloc access in imageblit
Summary
In the Linux kernel, the following vulnerability has been resolved: tty: Fix out-of-bound vmalloc access in imageblit This issue happens when a userspace program does an ioctl FBIOPUT_VSCREENINFO passing the fb_var_screeninfo struct containing only the fields xres, yres, and bits_per_pixel with values. If this struct is the same as the previous ioctl, the vc_resize() detects it and doesn't call the resize_screen(), leaving the fb_var_screeninfo incomplete. And this leads to the updatescrollmode() calculates a wrong value to fbcon_display->vrows, which makes the real_y() return a wrong value of y, and that value, eventually, causes the imageblit to access an out-of-bound address value. To solve this issue I made the resize_screen() be called even if the screen does not need any resizing, so it will "fix and fill" the fb_var_screeninfo independently.
Severity
7.8 (High)
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
SSVC
Exploitation: none Automatable: no Technical Impact: partial
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2024-06-17 17:37 UTC
Assigner
References
Impacted products
Vendor Product Version CPE status
Linux Linux Affected: 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 , < 7e71fcedfda6f7de18f850a6b36e78d78b04476f (git)
Affected: 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 , < 70aed03b1d5a5df974f456cdc8eedb213c94bb8b (git)
Affected: 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 , < 067c694d06040db6f0c65281bb358452ca6d85b9 (git)
Affected: 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 , < 8a6a240f52e14356386030d8958ae8b1761d2325 (git)
Affected: 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 , < 883f7897a25e3ce14a7f274ca4c73f49ac84002a (git)
Affected: 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 , < d570c48dd37dbe8fc6875d4461d01a9554ae2560 (git)
Affected: 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 , < 699d926585daa6ec44be556cdc1ab89e5d54557b (git)
Affected: 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 , < 3b0c406124719b625b1aba431659f5cdc24a982c (git)
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Linux Linux Affected: 2.6.12
Unaffected: 0 , < 2.6.12 (semver)
Unaffected: 4.4.286 , ≤ 4.4.* (semver)
Unaffected: 4.9.285 , ≤ 4.9.* (semver)
Unaffected: 4.14.249 , ≤ 4.14.* (semver)
Unaffected: 4.19.209 , ≤ 4.19.* (semver)
Unaffected: 5.4.151 , ≤ 5.4.* (semver)
Unaffected: 5.10.71 , ≤ 5.10.* (semver)
Unaffected: 5.14.10 , ≤ 5.14.* (semver)
Unaffected: 5.15 , ≤ * (original_commit_for_fix)
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              "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
              "vendor": "Linux",
              "versions": [
                {
                  "status": "affected",
                  "version": "2.6.12"
                },
                {
                  "lessThan": "2.6.12",
                  "status": "unaffected",
                  "version": "0",
                  "versionType": "semver"
                },
                {
                  "lessThanOrEqual": "4.4.*",
                  "status": "unaffected",
                  "version": "4.4.286",
                  "versionType": "semver"
                },
                {
                  "lessThanOrEqual": "4.9.*",
                  "status": "unaffected",
                  "version": "4.9.285",
                  "versionType": "semver"
                },
                {
                  "lessThanOrEqual": "4.14.*",
                  "status": "unaffected",
                  "version": "4.14.249",
                  "versionType": "semver"
                },
                {
                  "lessThanOrEqual": "4.19.*",
                  "status": "unaffected",
                  "version": "4.19.209",
                  "versionType": "semver"
                },
                {
                  "lessThanOrEqual": "5.4.*",
                  "status": "unaffected",
                  "version": "5.4.151",
                  "versionType": "semver"
                },
                {
                  "lessThanOrEqual": "5.10.*",
                  "status": "unaffected",
                  "version": "5.10.71",
                  "versionType": "semver"
                },
                {
                  "lessThanOrEqual": "5.14.*",
                  "status": "unaffected",
                  "version": "5.14.10",
                  "versionType": "semver"
                },
                {
                  "lessThanOrEqual": "*",
                  "status": "unaffected",
                  "version": "5.15",
                  "versionType": "original_commit_for_fix"
                }
              ]
            }
          ],
          "cpeApplicability": [
            {
              "nodes": [
                {
                  "cpeMatch": [
                    {
                      "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                      "versionEndExcluding": "4.4.286",
                      "versionStartIncluding": "2.6.12",
                      "vulnerable": true
                    },
                    {
                      "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                      "versionEndExcluding": "4.9.285",
                      "versionStartIncluding": "2.6.12",
                      "vulnerable": true
                    },
                    {
                      "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                      "versionEndExcluding": "4.14.249",
                      "versionStartIncluding": "2.6.12",
                      "vulnerable": true
                    },
                    {
                      "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                      "versionEndExcluding": "4.19.209",
                      "versionStartIncluding": "2.6.12",
                      "vulnerable": true
                    },
                    {
                      "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                      "versionEndExcluding": "5.4.151",
                      "versionStartIncluding": "2.6.12",
                      "vulnerable": true
                    },
                    {
                      "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                      "versionEndExcluding": "5.10.71",
                      "versionStartIncluding": "2.6.12",
                      "vulnerable": true
                    },
                    {
                      "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                      "versionEndExcluding": "5.14.10",
                      "versionStartIncluding": "2.6.12",
                      "vulnerable": true
                    },
                    {
                      "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                      "versionEndExcluding": "5.15",
                      "versionStartIncluding": "2.6.12",
                      "vulnerable": true
                    }
                  ],
                  "negate": false,
                  "operator": "OR"
                }
              ]
            }
          ],
          "descriptions": [
            {
              "lang": "en",
              "value": "In the Linux kernel, the following vulnerability has been resolved:\n\ntty: Fix out-of-bound vmalloc access in imageblit\n\nThis issue happens when a userspace program does an ioctl\nFBIOPUT_VSCREENINFO passing the fb_var_screeninfo struct\ncontaining only the fields xres, yres, and bits_per_pixel\nwith values.\n\nIf this struct is the same as the previous ioctl, the\nvc_resize() detects it and doesn\u0027t call the resize_screen(),\nleaving the fb_var_screeninfo incomplete. And this leads to\nthe updatescrollmode() calculates a wrong value to\nfbcon_display-\u003evrows, which makes the real_y() return a\nwrong value of y, and that value, eventually, causes\nthe imageblit to access an out-of-bound address value.\n\nTo solve this issue I made the resize_screen() be called\neven if the screen does not need any resizing, so it will\n\"fix and fill\" the fb_var_screeninfo independently."
            }
          ],
          "metrics": [
            {
              "cvssV3_1": {
                "baseScore": 7.8,
                "baseSeverity": "HIGH",
                "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
                "version": "3.1"
              },
              "scenarios": [
                {
                  "lang": "en",
                  "value": "AV:L - The bug is triggered by a local FBIOPUT_VSCREENINFO ioctl on /dev/fbN that flows through fb_set_var \u2192 fbcon_modechanged \u2192 vc_do_resize \u2192 updatescrollmode \u2192 imageblit; it is not reachable via network or adjacent protocols.\nAC:L - A crafted incomplete fb_var_screeninfo (undersized/zero virtual resolution) deterministically drives negative fbcon_display-\u003evrows and an OOB imageblit write; syzkaller has a reliable C repro with no race or attacker-independent conditions.\nPR:L - do_fb_ioctl/FBIOPUT_VSCREENINFO performs no capability check; access only requires opening /dev/fbN, which seated users, video-group members, and embedded/Android graphics processes commonly have without real root in the init namespace.\nUI:N - The attacker opens the framebuffer device and issues the ioctl directly; fbcon_modechanged calls update_screen on the same path, so no separate victim action is required.\nS:U - Impact is kernel memory corruption and crash within the same host security authority; it does not cross a VM, IOMMU, or other distinct boundary.\nC:H - The defect is kernel memory corruption via a vmalloc out-of-bounds access in imageblit; per guidance, such corruption can be leveraged for information disclosure and is scored High when uncertain.\nI:H - Syzbot confirms a KASAN vmalloc-out-of-bounds Write in fast_imageblit/sys_imageblit past screen_base; out-of-bounds writes are scored High because they enable memory corruption and potential control-flow hijacking.\nA:H - The out-of-bounds kernel write can oops/panic the kernel (and does under KASAN), which is a high availability impact."
                }
              ]
            }
          ],
          "providerMetadata": {
            "dateUpdated": "2026-08-05T08:47:33.469Z",
            "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
            "shortName": "Linux"
          },
          "references": [
            {
              "url": "https://git.kernel.org/stable/c/7e71fcedfda6f7de18f850a6b36e78d78b04476f"
            },
            {
              "url": "https://git.kernel.org/stable/c/70aed03b1d5a5df974f456cdc8eedb213c94bb8b"
            },
            {
              "url": "https://git.kernel.org/stable/c/067c694d06040db6f0c65281bb358452ca6d85b9"
            },
            {
              "url": "https://git.kernel.org/stable/c/8a6a240f52e14356386030d8958ae8b1761d2325"
            },
            {
              "url": "https://git.kernel.org/stable/c/883f7897a25e3ce14a7f274ca4c73f49ac84002a"
            },
            {
              "url": "https://git.kernel.org/stable/c/d570c48dd37dbe8fc6875d4461d01a9554ae2560"
            },
            {
              "url": "https://git.kernel.org/stable/c/699d926585daa6ec44be556cdc1ab89e5d54557b"
            },
            {
              "url": "https://git.kernel.org/stable/c/3b0c406124719b625b1aba431659f5cdc24a982c"
            }
          ],
          "title": "tty: Fix out-of-bound vmalloc access in imageblit",
          "x_generator": {
            "engine": "bippy-1.2.0"
          }
        }
      },
      "cveMetadata": {
        "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "assignerShortName": "Linux",
        "cveId": "CVE-2021-47383",
        "datePublished": "2024-05-21T15:03:44.286Z",
        "dateReserved": "2024-05-21T14:58:30.812Z",
        "dateUpdated": "2026-08-05T08:47:33.469Z",
        "state": "PUBLISHED"
      },
      "dataType": "CVE_RECORD",
      "dataVersion": "5.2"
    }
  }
}



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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.


Related by attack behaviour

Vulnerabilities whose description is nearest to this one in the vector space of the CIRCL/vulnerability-attack-technique-biencoder model. This is a similarity search over the bi-encoder space (plain cosine), not a classification, and it has no measured accuracy.