CVE-2024-53176 (GCVE-0-2024-53176)
Vulnerability from cvelistv5
Published
2024-12-27 13:49
Modified
2026-08-05 11:44
Severity ?
9.8 (Critical) - CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Summary
In the Linux kernel, the following vulnerability has been resolved: smb: During unmount, ensure all cached dir instances drop their dentry The unmount process (cifs_kill_sb() calling close_all_cached_dirs()) can race with various cached directory operations, which ultimately results in dentries not being dropped and these kernel BUGs: BUG: Dentry ffff88814f37e358{i=1000000000080,n=/} still in use (2) [unmount of cifs cifs] VFS: Busy inodes after unmount of cifs (cifs) ------------[ cut here ]------------ kernel BUG at fs/super.c:661! This happens when a cfid is in the process of being cleaned up when, and has been removed from the cfids->entries list, including: - Receiving a lease break from the server - Server reconnection triggers invalidate_all_cached_dirs(), which removes all the cfids from the list - The laundromat thread decides to expire an old cfid. To solve these problems, dropping the dentry is done in queued work done in a newly-added cfid_put_wq workqueue, and close_all_cached_dirs() flushes that workqueue after it drops all the dentries of which it's aware. This is a global workqueue (rather than scoped to a mount), but the queued work is minimal. The final cleanup work for cleaning up a cfid is performed via work queued in the serverclose_wq workqueue; this is done separate from dropping the dentries so that close_all_cached_dirs() doesn't block on any server operations. Both of these queued works expect to invoked with a cfid reference and a tcon reference to avoid those objects from being freed while the work is ongoing. While we're here, add proper locking to close_all_cached_dirs(), and locking around the freeing of cfid->dentry.
References
Impacted products
Vendor Product Version
Linux Linux Version: ebe98f1447bbccf8228335c62d86af02a0ed23f7
Version: ebe98f1447bbccf8228335c62d86af02a0ed23f7
Version: ebe98f1447bbccf8228335c62d86af02a0ed23f7
Version: ebe98f1447bbccf8228335c62d86af02a0ed23f7
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{
  "containers": {
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "fs/smb/client/cached_dir.c",
            "fs/smb/client/cached_dir.h",
            "fs/smb/client/cifsfs.c",
            "fs/smb/client/cifsglob.h",
            "fs/smb/client/inode.c",
            "fs/smb/client/trace.h"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
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          ]
        },
        {
          "defaultStatus": "affected",
          "product": "Linux",
          "programFiles": [
            "fs/smb/client/cached_dir.c",
            "fs/smb/client/cached_dir.h",
            "fs/smb/client/cifsfs.c",
            "fs/smb/client/cifsglob.h",
            "fs/smb/client/inode.c",
            "fs/smb/client/trace.h"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "status": "affected",
              "version": "6.1"
            },
            {
              "lessThan": "6.1",
              "status": "unaffected",
              "version": "0",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.6.*",
              "status": "unaffected",
              "version": "6.6.64",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.11.*",
              "status": "unaffected",
              "version": "6.11.11",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.12.*",
              "status": "unaffected",
              "version": "6.12.2",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "*",
              "status": "unaffected",
              "version": "6.13",
              "versionType": "original_commit_for_fix"
            }
          ]
        }
      ],
      "cpeApplicability": [
        {
          "nodes": [
            {
              "cpeMatch": [
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "6.6.64",
                  "versionStartIncluding": "6.1",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "6.11.11",
                  "versionStartIncluding": "6.1",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "6.12.2",
                  "versionStartIncluding": "6.1",
                  "vulnerable": true
                },
                {
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                  "versionEndExcluding": "6.13",
                  "versionStartIncluding": "6.1",
                  "vulnerable": true
                }
              ],
              "negate": false,
              "operator": "OR"
            }
          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nsmb: During unmount, ensure all cached dir instances drop their dentry\n\nThe unmount process (cifs_kill_sb() calling close_all_cached_dirs()) can\nrace with various cached directory operations, which ultimately results\nin dentries not being dropped and these kernel BUGs:\n\nBUG: Dentry ffff88814f37e358{i=1000000000080,n=/}  still in use (2) [unmount of cifs cifs]\nVFS: Busy inodes after unmount of cifs (cifs)\n------------[ cut here ]------------\nkernel BUG at fs/super.c:661!\n\nThis happens when a cfid is in the process of being cleaned up when, and\nhas been removed from the cfids-\u003eentries list, including:\n\n- Receiving a lease break from the server\n- Server reconnection triggers invalidate_all_cached_dirs(), which\n  removes all the cfids from the list\n- The laundromat thread decides to expire an old cfid.\n\nTo solve these problems, dropping the dentry is done in queued work done\nin a newly-added cfid_put_wq workqueue, and close_all_cached_dirs()\nflushes that workqueue after it drops all the dentries of which it\u0027s\naware. This is a global workqueue (rather than scoped to a mount), but\nthe queued work is minimal.\n\nThe final cleanup work for cleaning up a cfid is performed via work\nqueued in the serverclose_wq workqueue; this is done separate from\ndropping the dentries so that close_all_cached_dirs() doesn\u0027t block on\nany server operations.\n\nBoth of these queued works expect to invoked with a cfid reference and\na tcon reference to avoid those objects from being freed while the work\nis ongoing.\n\nWhile we\u0027re here, add proper locking to close_all_cached_dirs(), and\nlocking around the freeing of cfid-\u003edentry."
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "baseScore": 9.8,
            "baseSeverity": "CRITICAL",
            "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H",
            "version": "3.1"
          },
          "scenarios": [
            {
              "lang": "en",
              "value": "AV:N - The teardown side of the race is driven entirely by SMB traffic from the remote server over TCP/445 \u2014 an unsolicited SMB2 lease-break packet reaches `cached_dir_lease_break()` from `cifs_demultiplex_thread()`, and a dropped connection or `STATUS_NETWORK_NAME_DELETED` forces `invalidate_all_cached_dirs()`. A malicious, compromised, DFS-redirected, or on-path SMB server thus triggers the vulnerable window remotely.\nAC:L - The attacker fully controls one side of the race and can hold it open indefinitely \u2014 flooding lease breaks for every cached dir (default up to `max_cached_dirs`) or keeping the client in a reconnect loop leaves cfids off `cfids-\u003eentries` with dentries still held for a workqueue round-trip, while the unmount side is a routine, endlessly repeated event (autofs/systemd idle unmounts, container teardown, shutdown). No memory grooming, no non-default config (`dir_cache_timeout` defaults to 30), and unlimited retries across every client.\nPR:N - The malicious SMB server needs no credentials or privileges on the victim client; the client authenticates to the server, not the reverse, and lease-break frames are processed by the demux thread with no client-side authorization. Without enforced signing an off-path/on-path attacker can inject the break frames just as well.\nUI:N - No victim action is needed \u2014 the mount pre-exists, lease breaks and reconnect-driven invalidation are handled automatically by the kernel, and the racing unmount occurs unattended via automount idle timeouts, container/pod teardown, or system shutdown.\nS:U - The corruption is confined to the cifs client\u0027s own kernel objects (cached_fid, dentry, superblock) within the kernel\u0027s security authority; no VM, IOMMU, or sandbox boundary is crossed.\nC:H - The unlocked walk of `cfids-\u003eentries` races with `list_del()` plus `kfree(cfid)` in `free_cached_dir()`, so the unmount path dereferences a freed (and potentially reallocated) cached_fid and follows attacker-influenced pointers; combined with the dentry refcount underflow from the double `dput()`, this yields a use-after-free on dentry-cache objects leveragable for kernel memory disclosure.\nI:H - The race produces a double `dput()` of the same `cfid-\u003edentry` (the fix adds `fid_lock` around every read/clear of it), underflowing the dentry lockref and freeing a live dentry \u2014 a classic UAF write primitive via the dentry slab and its `d_op` vtable \u2014 plus a NULL store into an already-freed cached_fid object.\nA:H - The reported outcome is an outright kernel BUG \u2014 \"Dentry still in use\", \"VFS: Busy inodes after unmount\", and `BUG at fs/super.c` via `CHECK_DATA_CORRUPTION` \u2014 with surviving inodes poisoned by `VFS_PTR_POISON` and deferred `dput()`s touching a freed superblock, guaranteeing a panic or later oops."
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-08-05T11:44:23.051Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/73934e535cffbda1490fa97d82690a0f9aa73e94"
        },
        {
          "url": "https://git.kernel.org/stable/c/ff4528bbc82d0d90073751f7b49e7b9e9c7e5638"
        },
        {
          "url": "https://git.kernel.org/stable/c/548812afd96982a76a93ba76c0582ea670c40d9e"
        },
        {
          "url": "https://git.kernel.org/stable/c/3fa640d035e5ae526769615c35cb9ed4be6e3662"
        }
      ],
      "title": "smb: During unmount, ensure all cached dir instances drop their dentry",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2024-53176",
    "datePublished": "2024-12-27T13:49:20.518Z",
    "dateReserved": "2024-11-19T17:17:25.007Z",
    "dateUpdated": "2026-08-05T11:44:23.051Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}


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