CVE-2025-40040 (GCVE-0-2025-40040)
Vulnerability from cvelistv5
Published
2025-10-28 11:48
Modified
2025-10-29 13:19
Severity ?
Summary
In the Linux kernel, the following vulnerability has been resolved: mm/ksm: fix flag-dropping behavior in ksm_madvise syzkaller discovered the following crash: (kernel BUG) [ 44.607039] ------------[ cut here ]------------ [ 44.607422] kernel BUG at mm/userfaultfd.c:2067! [ 44.608148] Oops: invalid opcode: 0000 [#1] SMP DEBUG_PAGEALLOC KASAN NOPTI [ 44.608814] CPU: 1 UID: 0 PID: 2475 Comm: reproducer Not tainted 6.16.0-rc6 #1 PREEMPT(none) [ 44.609635] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014 [ 44.610695] RIP: 0010:userfaultfd_release_all+0x3a8/0x460 <snip other registers, drop unreliable trace> [ 44.617726] Call Trace: [ 44.617926] <TASK> [ 44.619284] userfaultfd_release+0xef/0x1b0 [ 44.620976] __fput+0x3f9/0xb60 [ 44.621240] fput_close_sync+0x110/0x210 [ 44.622222] __x64_sys_close+0x8f/0x120 [ 44.622530] do_syscall_64+0x5b/0x2f0 [ 44.622840] entry_SYSCALL_64_after_hwframe+0x76/0x7e [ 44.623244] RIP: 0033:0x7f365bb3f227 Kernel panics because it detects UFFD inconsistency during userfaultfd_release_all(). Specifically, a VMA which has a valid pointer to vma->vm_userfaultfd_ctx, but no UFFD flags in vma->vm_flags. The inconsistency is caused in ksm_madvise(): when user calls madvise() with MADV_UNMEARGEABLE on a VMA that is registered for UFFD in MINOR mode, it accidentally clears all flags stored in the upper 32 bits of vma->vm_flags. Assuming x86_64 kernel build, unsigned long is 64-bit and unsigned int and int are 32-bit wide. This setup causes the following mishap during the &= ~VM_MERGEABLE assignment. VM_MERGEABLE is a 32-bit constant of type unsigned int, 0x8000'0000. After ~ is applied, it becomes 0x7fff'ffff unsigned int, which is then promoted to unsigned long before the & operation. This promotion fills upper 32 bits with leading 0s, as we're doing unsigned conversion (and even for a signed conversion, this wouldn't help as the leading bit is 0). & operation thus ends up AND-ing vm_flags with 0x0000'0000'7fff'ffff instead of intended 0xffff'ffff'7fff'ffff and hence accidentally clears the upper 32-bits of its value. Fix it by changing `VM_MERGEABLE` constant to unsigned long, using the BIT() macro. Note: other VM_* flags are not affected: This only happens to the VM_MERGEABLE flag, as the other VM_* flags are all constants of type int and after ~ operation, they end up with leading 1 and are thus converted to unsigned long with leading 1s. Note 2: After commit 31defc3b01d9 ("userfaultfd: remove (VM_)BUG_ON()s"), this is no longer a kernel BUG, but a WARNING at the same place: [ 45.595973] WARNING: CPU: 1 PID: 2474 at mm/userfaultfd.c:2067 but the root-cause (flag-drop) remains the same. [akpm@linux-foundation.org: rust bindgen wasn't able to handle BIT(), from Miguel]
References
Impacted products
Vendor Product Version
Linux Linux Version: 7677f7fd8be76659cd2d0db8ff4093bbb51c20e5
Version: 7677f7fd8be76659cd2d0db8ff4093bbb51c20e5
Version: 7677f7fd8be76659cd2d0db8ff4093bbb51c20e5
Version: 7677f7fd8be76659cd2d0db8ff4093bbb51c20e5
Version: 7677f7fd8be76659cd2d0db8ff4093bbb51c20e5
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{
  "containers": {
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "include/linux/mm.h",
            "rust/bindings/bindings_helper.h"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "lessThan": "41cb9fd904fe0c39d52e82dd84dc3c96b7aa9693",
              "status": "affected",
              "version": "7677f7fd8be76659cd2d0db8ff4093bbb51c20e5",
              "versionType": "git"
            },
            {
              "lessThan": "92b82e232b8d8b116ac6e57aeae7a6033db92c60",
              "status": "affected",
              "version": "7677f7fd8be76659cd2d0db8ff4093bbb51c20e5",
              "versionType": "git"
            },
            {
              "lessThan": "ac50c6e0a8f91a02b681af81abb2362fbb67cc18",
              "status": "affected",
              "version": "7677f7fd8be76659cd2d0db8ff4093bbb51c20e5",
              "versionType": "git"
            },
            {
              "lessThan": "76385629f45740b7888f8fcd83bde955b10f61fe",
              "status": "affected",
              "version": "7677f7fd8be76659cd2d0db8ff4093bbb51c20e5",
              "versionType": "git"
            },
            {
              "lessThan": "f04aad36a07cc17b7a5d5b9a2d386ce6fae63e93",
              "status": "affected",
              "version": "7677f7fd8be76659cd2d0db8ff4093bbb51c20e5",
              "versionType": "git"
            }
          ]
        },
        {
          "defaultStatus": "affected",
          "product": "Linux",
          "programFiles": [
            "include/linux/mm.h",
            "rust/bindings/bindings_helper.h"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "status": "affected",
              "version": "5.13"
            },
            {
              "lessThan": "5.13",
              "status": "unaffected",
              "version": "0",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.1.*",
              "status": "unaffected",
              "version": "6.1.158",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.6.*",
              "status": "unaffected",
              "version": "6.6.114",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.12.*",
              "status": "unaffected",
              "version": "6.12.55",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.17.*",
              "status": "unaffected",
              "version": "6.17.3",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "*",
              "status": "unaffected",
              "version": "6.18-rc1",
              "versionType": "original_commit_for_fix"
            }
          ]
        }
      ],
      "cpeApplicability": [
        {
          "nodes": [
            {
              "cpeMatch": [
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "6.1.158",
                  "versionStartIncluding": "5.13",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "6.6.114",
                  "versionStartIncluding": "5.13",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "6.12.55",
                  "versionStartIncluding": "5.13",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "6.17.3",
                  "versionStartIncluding": "5.13",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "6.18-rc1",
                  "versionStartIncluding": "5.13",
                  "vulnerable": true
                }
              ],
              "negate": false,
              "operator": "OR"
            }
          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nmm/ksm: fix flag-dropping behavior in ksm_madvise\n\nsyzkaller discovered the following crash: (kernel BUG)\n\n[   44.607039] ------------[ cut here ]------------\n[   44.607422] kernel BUG at mm/userfaultfd.c:2067!\n[   44.608148] Oops: invalid opcode: 0000 [#1] SMP DEBUG_PAGEALLOC KASAN NOPTI\n[   44.608814] CPU: 1 UID: 0 PID: 2475 Comm: reproducer Not tainted 6.16.0-rc6 #1 PREEMPT(none)\n[   44.609635] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014\n[   44.610695] RIP: 0010:userfaultfd_release_all+0x3a8/0x460\n\n\u003csnip other registers, drop unreliable trace\u003e\n\n[   44.617726] Call Trace:\n[   44.617926]  \u003cTASK\u003e\n[   44.619284]  userfaultfd_release+0xef/0x1b0\n[   44.620976]  __fput+0x3f9/0xb60\n[   44.621240]  fput_close_sync+0x110/0x210\n[   44.622222]  __x64_sys_close+0x8f/0x120\n[   44.622530]  do_syscall_64+0x5b/0x2f0\n[   44.622840]  entry_SYSCALL_64_after_hwframe+0x76/0x7e\n[   44.623244] RIP: 0033:0x7f365bb3f227\n\nKernel panics because it detects UFFD inconsistency during\nuserfaultfd_release_all().  Specifically, a VMA which has a valid pointer\nto vma-\u003evm_userfaultfd_ctx, but no UFFD flags in vma-\u003evm_flags.\n\nThe inconsistency is caused in ksm_madvise(): when user calls madvise()\nwith MADV_UNMEARGEABLE on a VMA that is registered for UFFD in MINOR mode,\nit accidentally clears all flags stored in the upper 32 bits of\nvma-\u003evm_flags.\n\nAssuming x86_64 kernel build, unsigned long is 64-bit and unsigned int and\nint are 32-bit wide.  This setup causes the following mishap during the \u0026=\n~VM_MERGEABLE assignment.\n\nVM_MERGEABLE is a 32-bit constant of type unsigned int, 0x8000\u00270000. \nAfter ~ is applied, it becomes 0x7fff\u0027ffff unsigned int, which is then\npromoted to unsigned long before the \u0026 operation.  This promotion fills\nupper 32 bits with leading 0s, as we\u0027re doing unsigned conversion (and\neven for a signed conversion, this wouldn\u0027t help as the leading bit is 0).\n\u0026 operation thus ends up AND-ing vm_flags with 0x0000\u00270000\u00277fff\u0027ffff\ninstead of intended 0xffff\u0027ffff\u00277fff\u0027ffff and hence accidentally clears\nthe upper 32-bits of its value.\n\nFix it by changing `VM_MERGEABLE` constant to unsigned long, using the\nBIT() macro.\n\nNote: other VM_* flags are not affected: This only happens to the\nVM_MERGEABLE flag, as the other VM_* flags are all constants of type int\nand after ~ operation, they end up with leading 1 and are thus converted\nto unsigned long with leading 1s.\n\nNote 2:\nAfter commit 31defc3b01d9 (\"userfaultfd: remove (VM_)BUG_ON()s\"), this is\nno longer a kernel BUG, but a WARNING at the same place:\n\n[   45.595973] WARNING: CPU: 1 PID: 2474 at mm/userfaultfd.c:2067\n\nbut the root-cause (flag-drop) remains the same.\n\n[akpm@linux-foundation.org: rust bindgen wasn\u0027t able to handle BIT(), from Miguel]"
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2025-10-29T13:19:40.112Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/41cb9fd904fe0c39d52e82dd84dc3c96b7aa9693"
        },
        {
          "url": "https://git.kernel.org/stable/c/92b82e232b8d8b116ac6e57aeae7a6033db92c60"
        },
        {
          "url": "https://git.kernel.org/stable/c/ac50c6e0a8f91a02b681af81abb2362fbb67cc18"
        },
        {
          "url": "https://git.kernel.org/stable/c/76385629f45740b7888f8fcd83bde955b10f61fe"
        },
        {
          "url": "https://git.kernel.org/stable/c/f04aad36a07cc17b7a5d5b9a2d386ce6fae63e93"
        }
      ],
      "title": "mm/ksm: fix flag-dropping behavior in ksm_madvise",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2025-40040",
    "datePublished": "2025-10-28T11:48:20.395Z",
    "dateReserved": "2025-04-16T07:20:57.154Z",
    "dateUpdated": "2025-10-29T13:19:40.112Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.1",
  "vulnerability-lookup:meta": {
    "nvd": "{\"cve\":{\"id\":\"CVE-2025-40040\",\"sourceIdentifier\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\",\"published\":\"2025-10-28T12:15:37.967\",\"lastModified\":\"2025-10-30T15:05:32.197\",\"vulnStatus\":\"Awaiting Analysis\",\"cveTags\":[],\"descriptions\":[{\"lang\":\"en\",\"value\":\"In the Linux kernel, the following vulnerability has been resolved:\\n\\nmm/ksm: fix flag-dropping behavior in ksm_madvise\\n\\nsyzkaller discovered the following crash: (kernel BUG)\\n\\n[   44.607039] ------------[ cut here ]------------\\n[   44.607422] kernel BUG at mm/userfaultfd.c:2067!\\n[   44.608148] Oops: invalid opcode: 0000 [#1] SMP DEBUG_PAGEALLOC KASAN NOPTI\\n[   44.608814] CPU: 1 UID: 0 PID: 2475 Comm: reproducer Not tainted 6.16.0-rc6 #1 PREEMPT(none)\\n[   44.609635] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014\\n[   44.610695] RIP: 0010:userfaultfd_release_all+0x3a8/0x460\\n\\n\u003csnip other registers, drop unreliable trace\u003e\\n\\n[   44.617726] Call Trace:\\n[   44.617926]  \u003cTASK\u003e\\n[   44.619284]  userfaultfd_release+0xef/0x1b0\\n[   44.620976]  __fput+0x3f9/0xb60\\n[   44.621240]  fput_close_sync+0x110/0x210\\n[   44.622222]  __x64_sys_close+0x8f/0x120\\n[   44.622530]  do_syscall_64+0x5b/0x2f0\\n[   44.622840]  entry_SYSCALL_64_after_hwframe+0x76/0x7e\\n[   44.623244] RIP: 0033:0x7f365bb3f227\\n\\nKernel panics because it detects UFFD inconsistency during\\nuserfaultfd_release_all().  Specifically, a VMA which has a valid pointer\\nto vma-\u003evm_userfaultfd_ctx, but no UFFD flags in vma-\u003evm_flags.\\n\\nThe inconsistency is caused in ksm_madvise(): when user calls madvise()\\nwith MADV_UNMEARGEABLE on a VMA that is registered for UFFD in MINOR mode,\\nit accidentally clears all flags stored in the upper 32 bits of\\nvma-\u003evm_flags.\\n\\nAssuming x86_64 kernel build, unsigned long is 64-bit and unsigned int and\\nint are 32-bit wide.  This setup causes the following mishap during the \u0026=\\n~VM_MERGEABLE assignment.\\n\\nVM_MERGEABLE is a 32-bit constant of type unsigned int, 0x8000\u00270000. \\nAfter ~ is applied, it becomes 0x7fff\u0027ffff unsigned int, which is then\\npromoted to unsigned long before the \u0026 operation.  This promotion fills\\nupper 32 bits with leading 0s, as we\u0027re doing unsigned conversion (and\\neven for a signed conversion, this wouldn\u0027t help as the leading bit is 0).\\n\u0026 operation thus ends up AND-ing vm_flags with 0x0000\u00270000\u00277fff\u0027ffff\\ninstead of intended 0xffff\u0027ffff\u00277fff\u0027ffff and hence accidentally clears\\nthe upper 32-bits of its value.\\n\\nFix it by changing `VM_MERGEABLE` constant to unsigned long, using the\\nBIT() macro.\\n\\nNote: other VM_* flags are not affected: This only happens to the\\nVM_MERGEABLE flag, as the other VM_* flags are all constants of type int\\nand after ~ operation, they end up with leading 1 and are thus converted\\nto unsigned long with leading 1s.\\n\\nNote 2:\\nAfter commit 31defc3b01d9 (\\\"userfaultfd: remove (VM_)BUG_ON()s\\\"), this is\\nno longer a kernel BUG, but a WARNING at the same place:\\n\\n[   45.595973] WARNING: CPU: 1 PID: 2474 at mm/userfaultfd.c:2067\\n\\nbut the root-cause (flag-drop) remains the same.\\n\\n[akpm@linux-foundation.org: rust bindgen wasn\u0027t able to handle BIT(), from Miguel]\"}],\"metrics\":{},\"references\":[{\"url\":\"https://git.kernel.org/stable/c/41cb9fd904fe0c39d52e82dd84dc3c96b7aa9693\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"},{\"url\":\"https://git.kernel.org/stable/c/76385629f45740b7888f8fcd83bde955b10f61fe\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"},{\"url\":\"https://git.kernel.org/stable/c/92b82e232b8d8b116ac6e57aeae7a6033db92c60\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"},{\"url\":\"https://git.kernel.org/stable/c/ac50c6e0a8f91a02b681af81abb2362fbb67cc18\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"},{\"url\":\"https://git.kernel.org/stable/c/f04aad36a07cc17b7a5d5b9a2d386ce6fae63e93\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"}]}}"
  }
}


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