xfs: check for deleted cursors when revalidating two btrees

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Summary

CVECVE-2026-23249
StatePUBLISHED
AssignerLinux
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-03-18 18:16:22 UTC
Updated2026-05-21 18:34:07 UTC
DescriptionIn the Linux kernel, the following vulnerability has been resolved: xfs: check for deleted cursors when revalidating two btrees The free space and inode btree repair functions will rebuild both btrees at the same time, after which it needs to evaluate both btrees to confirm that the corruptions are gone. However, Jiaming Zhang ran syzbot and produced a crash in the second xchk_allocbt call. His root-cause analysis is as follows (with minor corrections): In xrep_revalidate_allocbt(), xchk_allocbt() is called twice (first for BNOBT, second for CNTBT). The cause of this issue is that the first call nullified the cursor required by the second call. Let's first enter xrep_revalidate_allocbt() via following call chain: xfs_file_ioctl() -> xfs_ioc_scrubv_metadata() -> xfs_scrub_metadata() -> `sc->ops->repair_eval(sc)` -> xrep_revalidate_allocbt() xchk_allocbt() is called twice in this function. In the first call: /* Note that sc->sm->sm_type is XFS_SCRUB_TYPE_BNOPT now */ xchk_allocbt() -> xchk_btree() -> `bs->scrub_rec(bs, recp)` -> xchk_allocbt_rec() -> xchk_allocbt_xref() -> xchk_allocbt_xref_other() since sm_type is XFS_SCRUB_TYPE_BNOBT, pur is set to &sc->sa.cnt_cur. Kernel called xfs_alloc_get_rec() and returned -EFSCORRUPTED. Call chain: xfs_alloc_get_rec() -> xfs_btree_get_rec() -> xfs_btree_check_block() -> (XFS_IS_CORRUPT || XFS_TEST_ERROR), the former is false and the latter is true, return -EFSCORRUPTED. This should be caused by ioctl$XFS_IOC_ERROR_INJECTION I guess. Back to xchk_allocbt_xref_other(), after receiving -EFSCORRUPTED from xfs_alloc_get_rec(), kernel called xchk_should_check_xref(). In this function, *curpp (points to sc->sa.cnt_cur) is nullified. Back to xrep_revalidate_allocbt(), since sc->sa.cnt_cur has been nullified, it then triggered null-ptr-deref via xchk_allocbt() (second call) -> xchk_btree(). So. The bnobt revalidation failed on a cross-reference attempt, so we deleted the cntbt cursor, and then crashed when we tried to revalidate the cntbt. Therefore, check for a null cntbt cursor before that revalidation, and mark the repair incomplete. Also we can ignore the second tree entirely if the first tree was rebuilt but is already corrupt. Apply the same fix to xrep_revalidate_iallocbt because it has the same problem.

Risk And Classification

Primary CVSS: v3.1 5.5 MEDIUM from [email protected]

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

Problem Types: CWE-476

CVSS v3.1 Breakdown

Attack Vector
Local
Attack Complexity
Low
Privileges Required
Low
User Interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

NVD Known Affected Configurations (CPE 2.3)

TypeVendorProductVersionUpdateEditionLanguage
Operating System Linux Linux Kernel All All All All

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Linux Linux affected dbfbf3bdf639a20da7d5fb390cd2e197d25aa418 d69de525bc7ab27713342080bf50826df3f6a68f git Not specified
CNA Linux Linux affected dbfbf3bdf639a20da7d5fb390cd2e197d25aa418 b04baa848c0543b240b1bd8aecff470382f6f154 git Not specified
CNA Linux Linux affected dbfbf3bdf639a20da7d5fb390cd2e197d25aa418 5991e96f2ae82df60a3e4ed00f3432d9f3502a99 git Not specified
CNA Linux Linux affected dbfbf3bdf639a20da7d5fb390cd2e197d25aa418 55e03b8cbe2783ec9acfb88e8adb946ed504e117 git Not specified
CNA Linux Linux affected 6.8 Not specified
CNA Linux Linux unaffected 6.8 semver Not specified
CNA Linux Linux unaffected 6.12.75 6.12.* semver Not specified
CNA Linux Linux unaffected 6.18.16 6.18.* semver Not specified
CNA Linux Linux unaffected 6.19.6 6.19.* semver Not specified
CNA Linux Linux unaffected 7.0 * original_commit_for_fix Not specified

References

ReferenceSourceLinkTags
git.kernel.org/stable/c/b04baa848c0543b240b1bd8aecff470382f6f154 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
git.kernel.org/stable/c/5991e96f2ae82df60a3e4ed00f3432d9f3502a99 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
git.kernel.org/stable/c/d69de525bc7ab27713342080bf50826df3f6a68f 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
git.kernel.org/stable/c/55e03b8cbe2783ec9acfb88e8adb946ed504e117 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
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