nfsd: cap decoded POSIX ACL count to bound sort cost

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Summary

CVECVE-2026-89695
StatePUBLISHED
AssignerLinux
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-09-11 20:19:56 UTC
Updated2026-09-11 20:19:56 UTC
DescriptionIn the Linux kernel, the following vulnerability has been resolved: nfsd: cap decoded POSIX ACL count to bound sort cost nfsd4_decode_posixacl() reads a u32 entry count off the wire and passes it straight to posix_acl_alloc() and sort_pacl_range(). The latter is an O(n^2) bubble sort, so a client-chosen count drives unbounded CPU in the server's compound processing path. nfsd4_decode_posixacl() xdr_stream_decode_u32(&count) /* uncapped u32 */ posix_acl_alloc(count, GFP_KERNEL) sort_pacl_range(*acl, 0, count - 1) /* O(n^2) bubble sort */ The encoder side in the same file already rejects ACLs whose a_count exceeds NFS_ACL_MAX_ENTRIES, but the decoder introduced in commit 5fc51dfc2eb1 ("NFSD: Add support for XDR decoding POSIX draft ACLs") omitted the symmetric check. Fix by rejecting a wire count greater than NFS_ACL_MAX_ENTRIES with nfserr_inval, before any allocation, so the sort is bounded by NFS_ACL_MAX_ENTRIES^2 comparisons. While we're in here, also fix the nfserr_resource return if posix_acl_alloc() fails. That's not a legal error code for v4.1+. Change it to return nfserr_jukebox as that's more appropriate for memory allocation failures.

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Linux Linux affected 5fc51dfc2eb160bd7ab3251ab1767cacf9c8bf05 ea14d71d6ecb925673761bcf79f781f7dc9042cc git Not specified
CNA Linux Linux affected 5fc51dfc2eb160bd7ab3251ab1767cacf9c8bf05 4bc1108e876153a2dd6d874052b99182c3603135 git Not specified
CNA Linux Linux affected 7.0 Not specified
CNA Linux Linux unaffected 7.0 semver Not specified
CNA Linux Linux unaffected 7.2.4 7.2.* semver Not specified
CNA Linux Linux unaffected 7.3-rc1 * original_commit_for_fix Not specified

References

ReferenceSourceLinkTags
git.kernel.org/stable/c/ea14d71d6ecb925673761bcf79f781f7dc9042cc 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/4bc1108e876153a2dd6d874052b99182c3603135 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
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