nfsd: hold rcu across localio cmpxchg retry

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-89670
StatePUBLISHED
AssignerLinux
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-09-11 20:19:53 UTC
Updated2026-09-11 20:19:53 UTC
DescriptionIn the Linux kernel, the following vulnerability has been resolved: nfsd: hold rcu across localio cmpxchg retry nfsd_file objects are freed via call_rcu (filecache.c:296), and nfsd_file_slab is created without SLAB_TYPESAFE_BY_RCU (KMEM_CACHE(nfsd_file, 0) at filecache.c:789), so the slab page backing a freed nfsd_file becomes freely reclaimable once the RCU grace period elapses. The again: retry block in nfsd_open_local_fh() loads a pointer with cmpxchg and then calls nfsd_file_get(new) (which is refcount_inc_not_zero) without holding rcu_read_lock. The sole caller nfs_open_local_fh() drops rcu_read_lock before invoking this helper, so no outer reader-side critical section covers the load. CPU 0 (nfsd_open_local_fh) CPU 1 (nfsd_file_put_local) ----- ----- new = cmpxchg(pnf, NULL, ...) nf = xchg(pnf, NULL) nfsd_file_put(nf) last ref -> call_rcu() /* grace period elapses; slab page recycled */ nfsd_file_get(new) refcount_inc_not_zero(&new->nf_ref) /* operates on recycled memory */ A non-zero word at the nf_ref offset of the recycled object makes the refcount bump appear to succeed, and the caller then dereferences new->nf_net and new->nf_file out of freed memory. Fix by taking rcu_read_lock() immediately before the cmpxchg and releasing it on all three exits of the if (new) block: the goto-again retry, the lost-race cleanup path, and the install-succeeded path. nfsd_file_put() and nfsd_net_put() stay outside the RCU section so they remain free to block.

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Linux Linux affected e6f7e1487ab528a6c653bd0d42812ff2942846cd 763c0bad872368304db718f79af7e93048885c67 git Not specified
CNA Linux Linux affected e6f7e1487ab528a6c653bd0d42812ff2942846cd 559570f91a7d4d199a72105e4980bef791f4cbf1 git Not specified
CNA Linux Linux affected e6f7e1487ab528a6c653bd0d42812ff2942846cd 58884694978a3d7d111edb433d7fd6a6c5af2f34 git Not specified
CNA Linux Linux affected 986a21ace186433e0397a59491646edad8c8d636 git Not specified
CNA Linux Linux affected 6.15.3 6.16 semver Not specified
CNA Linux Linux affected 6.16 Not specified
CNA Linux Linux unaffected 6.16 semver Not specified
CNA Linux Linux unaffected 6.18.50 6.18.* 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/559570f91a7d4d199a72105e4980bef791f4cbf1 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/763c0bad872368304db718f79af7e93048885c67 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/58884694978a3d7d111edb433d7fd6a6c5af2f34 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
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