{ "dataType": "CVE_RECORD", "dataVersion": "5.2", "cveMetadata": { "cveId": "CVE-2024-53176", "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "state": "PUBLISHED", "assignerShortName": "Linux", "dateReserved": "2024-11-19T17:17:25.007Z", "datePublished": "2024-12-27T13:49:20.518Z", "dateUpdated": "2026-08-05T11:44:23.051Z" }, "containers": { "cna": { "providerMetadata": { "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "shortName": "Linux", "dateUpdated": "2026-08-05T11:44:23.051Z" }, "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->entries 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's\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't 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're here, add proper locking to close_all_cached_dirs(), and\nlocking around the freeing of cfid->dentry." } ], "metrics": [ { "cvssV3_1": { "version": "3.1", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H", "baseScore": 9.8, "baseSeverity": "CRITICAL" }, "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 — 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 — 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->entries` 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 — 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's own kernel objects (cached_fid, dentry, superblock) within the kernel's security authority; no VM, IOMMU, or sandbox boundary is crossed.\nC:H - The unlocked walk of `cfids->entries` 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->dentry` (the fix adds `fid_lock` around every read/clear of it), underflowing the dentry lockref and freeing a live dentry — a classic UAF write primitive via the dentry slab and its `d_op` vtable — plus a NULL store into an already-freed cached_fid object.\nA:H - The reported outcome is an outright kernel BUG — \"Dentry still in use\", \"VFS: Busy inodes after unmount\", and `BUG at fs/super.c` via `CHECK_DATA_CORRUPTION` — with surviving inodes poisoned by `VFS_PTR_POISON` and deferred `dput()`s touching a freed superblock, guaranteeing a panic or later oops." } ] } ], "affected": [ { "product": "Linux", "vendor": "Linux", "defaultStatus": "unaffected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "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" ], "versions": [ { "version": "ebe98f1447bbccf8228335c62d86af02a0ed23f7", "lessThan": "73934e535cffbda1490fa97d82690a0f9aa73e94", "status": "affected", "versionType": "git" }, { "version": "ebe98f1447bbccf8228335c62d86af02a0ed23f7", "lessThan": "ff4528bbc82d0d90073751f7b49e7b9e9c7e5638", "status": "affected", "versionType": "git" }, { "version": "ebe98f1447bbccf8228335c62d86af02a0ed23f7", "lessThan": "548812afd96982a76a93ba76c0582ea670c40d9e", "status": "affected", "versionType": "git" }, { "version": "ebe98f1447bbccf8228335c62d86af02a0ed23f7", "lessThan": "3fa640d035e5ae526769615c35cb9ed4be6e3662", "status": "affected", "versionType": "git" } ] }, { "product": "Linux", "vendor": "Linux", "defaultStatus": "affected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "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" ], "versions": [ { "version": "6.1", "status": "affected" }, { "version": "0", "lessThan": "6.1", "status": "unaffected", "versionType": "semver" }, { "version": "6.6.64", "lessThanOrEqual": "6.6.*", "status": "unaffected", "versionType": "semver" }, { "version": "6.11.11", "lessThanOrEqual": "6.11.*", "status": "unaffected", "versionType": "semver" }, { "version": "6.12.2", "lessThanOrEqual": "6.12.*", "status": "unaffected", "versionType": "semver" }, { "version": "6.13", "lessThanOrEqual": "*", "status": "unaffected", "versionType": "original_commit_for_fix" } ] } ], "cpeApplicability": [ { "nodes": [ { "operator": "OR", "negate": false, "cpeMatch": [ { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.1", "versionEndExcluding": "6.6.64" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.1", "versionEndExcluding": "6.11.11" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.1", "versionEndExcluding": "6.12.2" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.1", "versionEndExcluding": "6.13" } ] } ] } ], "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" } } } }