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CVE-2026-74482

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

Published
Last modified
published
Not listed in CISA KEV
Fix
Fixed in 5.10.265, 5.15.216, 6.1.183, 6.6.151, 6.12.103, and 2 more
None on Exploit-DB, Metasploit or GitHub
  • Exploitation: none
  • Automatable: no
  • Technical impact: total

Summary

In 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.

Timeline

  1. CVE published
  2. CISA SSVC assessment

    Exploitation: none · Automatable: no · Technical impact: total

  3. Record last updated

Affected versions

  • Linux Linux

    From baa355fd331424526e742d41d9b90d5f9d10f716 · fixed in bc2f5eabaaf60ec18da70b619a8fba1bfb7dea3a; From baa355fd331424526e742d41d9b90d5f9d10f716 · fixed in f87c08060818ebb19bafed37c38244538da25097; From baa355fd331424526e742d41d9b90d5f9d10f716 · fixed in 6f5c272d71845a669e4c8ee5c72b376e29a0e6e5; From baa355fd331424526e742d41d9b90d5f9d10f716 · fixed in be106f7855f03d3128ed0ce70ba74b484a90b473; From baa355fd331424526e742d41d9b90d5f9d10f716 · fixed in e3dd774dbfd0b5bc2dbd0995221751b1234f8205; From baa355fd331424526e742d41d9b90d5f9d10f716 · fixed in 10065fb891651d9541e7a5a2db84c1e656ece4f9; From baa355fd331424526e742d41d9b90d5f9d10f716 · fixed in d640efe94d86d3be893d4c19220362546a637e90; From baa355fd331424526e742d41d9b90d5f9d10f716 · fixed in e923bd21058ea02fd0dcd3549d151d143fd036e5

  • Linux Linux

    4.8

  • KernelLinux

    From 4.8.0 · fixed in 5.10.265; From 5.11.0 · fixed in 5.15.216; From 5.16.0 · fixed in 6.1.183; From 6.2.0 · fixed in 6.6.151; From 6.7.0 · fixed in 6.12.103; From 6.13.0 · fixed in 6.18.44; From 6.19.0 · fixed in 7.1.8

References 8

git.kernel.org