mm/huge_memory: unlock i_mmap_rwsem before releasing after-split folios

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-74482
StatePUBLISHED
AssignerLinux
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-08-15 13:17:53 UTC
Updated2026-08-15 13:17:53 UTC
DescriptionIn the Linux kernel, the following vulnerability has been resolved: mm/huge_memory: unlock i_mmap_rwsem before releasing after-split folios __folio_split() keeps dereferencing the mapping after the split: shmem_uncharge(mapping->host) and remap_page() while the folios are still frozen/locked, and i_mmap_unlock_read(mapping) at the very end, after the after-split folios have been unlocked and freed. Nothing holds an inode reference across that. The split relies on @folio -- which the beyond-EOF drop loop never removes, as it starts at folio_next(folio) -- staying locked and in the page cache to hold off eviction. But the unlock loop unlocks @folio before i_mmap_unlock_read() runs. If the caller's @lock_at is a tail beyond EOF, as memory_failure() passes when splitting a poisoned tail of a shmem THP that reaches past i_size during truncation, it too is gone from the page cache; so once @folio is unlocked no locked, in-cache folio pins the inode, and a concurrent final iput() can evict and RCU-free it before i_mmap_unlock_read() touches i_mmap_rwsem: BUG: KASAN: slab-use-after-free in __up_read+0x634/0x790 i_mmap_unlock_read include/linux/fs.h:537 [inline] __folio_split+0x732/0x1640 mm/huge_memory.c:4100 try_to_split_thp_page+0xab/0x390 mm/memory-failure.c:1675 memory_failure+0x1394/0x26e0 mm/memory-failure.c:2470 Freed by task 4601: shmem_free_in_core_inode+0x54/0xb0 mm/shmem.c:5177 evict+0x57f/0xac0 fs/inode.c:870 Do every mapping dereference while @folio still pins the inode: drop i_mmap_rwsem right after remap_page(), before the loop that unlocks and frees the after-split folios, and clear @mapping so the exit path does not unlock it again. shmem_uncharge() and remap_page() already run before that point, so after this nothing past the unlock loop touches the inode or the mapping. This is now a rule the split depends on, alongside keeping @folio frozen until the page cache is updated: no inode or mapping dereference once the after-split folios start being unlocked.

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Linux Linux affected baa355fd331424526e742d41d9b90d5f9d10f716 be106f7855f03d3128ed0ce70ba74b484a90b473 git Not specified
CNA Linux Linux affected baa355fd331424526e742d41d9b90d5f9d10f716 e3dd774dbfd0b5bc2dbd0995221751b1234f8205 git Not specified
CNA Linux Linux affected baa355fd331424526e742d41d9b90d5f9d10f716 10065fb891651d9541e7a5a2db84c1e656ece4f9 git Not specified
CNA Linux Linux affected baa355fd331424526e742d41d9b90d5f9d10f716 d640efe94d86d3be893d4c19220362546a637e90 git Not specified
CNA Linux Linux affected baa355fd331424526e742d41d9b90d5f9d10f716 e923bd21058ea02fd0dcd3549d151d143fd036e5 git Not specified
CNA Linux Linux affected 4.8 Not specified
CNA Linux Linux unaffected 4.8 semver Not specified
CNA Linux Linux unaffected 6.6.151 6.6.* semver Not specified
CNA Linux Linux unaffected 6.12.103 6.12.* semver Not specified
CNA Linux Linux unaffected 6.18.44 6.18.* semver Not specified
CNA Linux Linux unaffected 7.1.8 7.1.* semver Not specified
CNA Linux Linux unaffected 7.2-rc6 * original_commit_for_fix Not specified

References

ReferenceSourceLinkTags
git.kernel.org/stable/c/e3dd774dbfd0b5bc2dbd0995221751b1234f8205 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/e923bd21058ea02fd0dcd3549d151d143fd036e5 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/10065fb891651d9541e7a5a2db84c1e656ece4f9 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/d640efe94d86d3be893d4c19220362546a637e90 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/be106f7855f03d3128ed0ce70ba74b484a90b473 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
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