{"id":"CVE-2026-74482","state":"PUBLISHED","title":"mm/huge_memory: unlock i_mmap_rwsem before releasing after-split folios","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nmm/huge_memory: unlock i_mmap_rwsem before releasing after-split folios\n\n__folio_split() keeps dereferencing the mapping after the split:\nshmem_uncharge(mapping->host) and remap_page() while the folios are still\nfrozen/locked, and i_mmap_unlock_read(mapping) at the very end, after the\nafter-split folios have been unlocked and freed.\n\nNothing holds an inode reference across that.  The split relies on @folio\n-- which the beyond-EOF drop loop never removes, as it starts at\nfolio_next(folio) -- staying locked and in the page cache to hold off\neviction.  But the unlock loop unlocks @folio before i_mmap_unlock_read()\nruns.  If the caller's @lock_at is a tail beyond EOF, as memory_failure()\npasses when splitting a poisoned tail of a shmem THP that reaches past\ni_size during truncation, it too is gone from the page cache; so once\n@folio is unlocked no locked, in-cache folio pins the inode, and a\nconcurrent final iput() can evict and RCU-free it before\ni_mmap_unlock_read() touches i_mmap_rwsem:\n\n  BUG: KASAN: slab-use-after-free in __up_read+0x634/0x790\n   i_mmap_unlock_read include/linux/fs.h:537 [inline]\n   __folio_split+0x732/0x1640 mm/huge_memory.c:4100\n   try_to_split_thp_page+0xab/0x390 mm/memory-failure.c:1675\n   memory_failure+0x1394/0x26e0 mm/memory-failure.c:2470\n\n  Freed by task 4601:\n   shmem_free_in_core_inode+0x54/0xb0 mm/shmem.c:5177\n   evict+0x57f/0xac0 fs/inode.c:870\n\nDo every mapping dereference while @folio still pins the inode: drop\ni_mmap_rwsem right after remap_page(), before the loop that unlocks and\nfrees the after-split folios, and clear @mapping so the exit path does not\nunlock it again.  shmem_uncharge() and remap_page() already run before\nthat point, so after this nothing past the unlock loop touches the inode\nor the mapping.\n\nThis is now a rule the split depends on, alongside keeping @folio frozen\nuntil the page cache is updated: no inode or mapping dereference once the\nafter-split folios start being unlocked.","publishedAt":"2026-08-15T12:27:15.083Z","updatedAt":"2026-10-16T19:05:49.129Z","severity":{"score":7.8,"label":"High","version":"3.1","vector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H","source":"Linux"},"assigner":"Linux","products":["Linux Linux"],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"baa355fd331424526e742d41d9b90d5f9d10f716","status":"affected","lessThan":"bc2f5eabaaf60ec18da70b619a8fba1bfb7dea3a","versionType":"git"},{"version":"baa355fd331424526e742d41d9b90d5f9d10f716","status":"affected","lessThan":"f87c08060818ebb19bafed37c38244538da25097","versionType":"git"},{"version":"baa355fd331424526e742d41d9b90d5f9d10f716","status":"affected","lessThan":"6f5c272d71845a669e4c8ee5c72b376e29a0e6e5","versionType":"git"},{"version":"baa355fd331424526e742d41d9b90d5f9d10f716","status":"affected","lessThan":"be106f7855f03d3128ed0ce70ba74b484a90b473","versionType":"git"},{"version":"baa355fd331424526e742d41d9b90d5f9d10f716","status":"affected","lessThan":"e3dd774dbfd0b5bc2dbd0995221751b1234f8205","versionType":"git"},{"version":"baa355fd331424526e742d41d9b90d5f9d10f716","status":"affected","lessThan":"10065fb891651d9541e7a5a2db84c1e656ece4f9","versionType":"git"},{"version":"baa355fd331424526e742d41d9b90d5f9d10f716","status":"affected","lessThan":"d640efe94d86d3be893d4c19220362546a637e90","versionType":"git"},{"version":"baa355fd331424526e742d41d9b90d5f9d10f716","status":"affected","lessThan":"e923bd21058ea02fd0dcd3549d151d143fd036e5","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["mm/huge_memory.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"4.8","status":"affected"},{"version":"0","status":"unaffected","lessThan":"4.8","versionType":"semver"},{"version":"5.10.265","status":"unaffected","lessThanOrEqual":"5.10.*","versionType":"semver"},{"version":"5.15.216","status":"unaffected","lessThanOrEqual":"5.15.*","versionType":"semver"},{"version":"6.1.183","status":"unaffected","lessThanOrEqual":"6.1.*","versionType":"semver"},{"version":"6.6.151","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.103","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.44","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"7.1.8","status":"unaffected","lessThanOrEqual":"7.1.*","versionType":"semver"},{"version":"7.2","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["mm/huge_memory.c"]}],"references":["https://git.kernel.org/stable/c/bc2f5eabaaf60ec18da70b619a8fba1bfb7dea3a","https://git.kernel.org/stable/c/f87c08060818ebb19bafed37c38244538da25097","https://git.kernel.org/stable/c/6f5c272d71845a669e4c8ee5c72b376e29a0e6e5","https://git.kernel.org/stable/c/be106f7855f03d3128ed0ce70ba74b484a90b473","https://git.kernel.org/stable/c/e3dd774dbfd0b5bc2dbd0995221751b1234f8205","https://git.kernel.org/stable/c/10065fb891651d9541e7a5a2db84c1e656ece4f9","https://git.kernel.org/stable/c/d640efe94d86d3be893d4c19220362546a637e90","https://git.kernel.org/stable/c/e923bd21058ea02fd0dcd3549d151d143fd036e5"],"weaknesses":[],"ingestedAt":"2026-10-29T20:12:58.252Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/74xxx/CVE-2026-74482.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-74482","state":"PUBLISHED","datePublished":"2026-08-15T12:27:15.083Z","dateUpdated":"2026-10-16T19:05:49.129Z","assignerShortName":"Linux","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateReserved":"2026-08-15T05:44:03.904Z"},"containers":{"cna":{"title":"mm/huge_memory: unlock i_mmap_rwsem before releasing after-split folios","descriptions":[{"lang":"en","value":"In the Linux kernel, the following vulnerability has been resolved:\n\nmm/huge_memory: unlock i_mmap_rwsem before releasing after-split folios\n\n__folio_split() keeps dereferencing the mapping after the split:\nshmem_uncharge(mapping->host) and remap_page() while the folios are still\nfrozen/locked, and i_mmap_unlock_read(mapping) at the very end, after the\nafter-split folios have been unlocked and freed.\n\nNothing holds an inode reference across that.  The split relies on @folio\n-- which the beyond-EOF drop loop never removes, as it starts at\nfolio_next(folio) -- staying locked and in the page cache to hold off\neviction.  But the unlock loop unlocks @folio before i_mmap_unlock_read()\nruns.  If the caller's @lock_at is a tail beyond EOF, as memory_failure()\npasses when splitting a poisoned tail of a shmem THP that reaches past\ni_size during truncation, it too is gone from the page cache; so once\n@folio is unlocked no locked, in-cache folio pins the inode, and a\nconcurrent final iput() can evict and RCU-free it before\ni_mmap_unlock_read() touches i_mmap_rwsem:\n\n  BUG: KASAN: slab-use-after-free in __up_read+0x634/0x790\n   i_mmap_unlock_read include/linux/fs.h:537 [inline]\n   __folio_split+0x732/0x1640 mm/huge_memory.c:4100\n   try_to_split_thp_page+0xab/0x390 mm/memory-failure.c:1675\n   memory_failure+0x1394/0x26e0 mm/memory-failure.c:2470\n\n  Freed by task 4601:\n   shmem_free_in_core_inode+0x54/0xb0 mm/shmem.c:5177\n   evict+0x57f/0xac0 fs/inode.c:870\n\nDo every mapping dereference while @folio still pins the inode: drop\ni_mmap_rwsem right after remap_page(), before the loop that unlocks and\nfrees the after-split folios, and clear @mapping so the exit path does not\nunlock it again.  shmem_uncharge() and remap_page() already run before\nthat point, so after this nothing past the unlock loop touches the inode\nor the mapping.\n\nThis is now a rule the split depends on, alongside keeping @folio frozen\nuntil the page cache is updated: no inode or mapping dereference once the\nafter-split folios start being unlocked."}],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"baa355fd331424526e742d41d9b90d5f9d10f716","status":"affected","lessThan":"bc2f5eabaaf60ec18da70b619a8fba1bfb7dea3a","versionType":"git"},{"version":"baa355fd331424526e742d41d9b90d5f9d10f716","status":"affected","lessThan":"f87c08060818ebb19bafed37c38244538da25097","versionType":"git"},{"version":"baa355fd331424526e742d41d9b90d5f9d10f716","status":"affected","lessThan":"6f5c272d71845a669e4c8ee5c72b376e29a0e6e5","versionType":"git"},{"version":"baa355fd331424526e742d41d9b90d5f9d10f716","status":"affected","lessThan":"be106f7855f03d3128ed0ce70ba74b484a90b473","versionType":"git"},{"version":"baa355fd331424526e742d41d9b90d5f9d10f716","status":"affected","lessThan":"e3dd774dbfd0b5bc2dbd0995221751b1234f8205","versionType":"git"},{"version":"baa355fd331424526e742d41d9b90d5f9d10f716","status":"affected","lessThan":"10065fb891651d9541e7a5a2db84c1e656ece4f9","versionType":"git"},{"version":"baa355fd331424526e742d41d9b90d5f9d10f716","status":"affected","lessThan":"d640efe94d86d3be893d4c19220362546a637e90","versionType":"git"},{"version":"baa355fd331424526e742d41d9b90d5f9d10f716","status":"affected","lessThan":"e923bd21058ea02fd0dcd3549d151d143fd036e5","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["mm/huge_memory.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"4.8","status":"affected"},{"version":"0","status":"unaffected","lessThan":"4.8","versionType":"semver"},{"version":"5.10.265","status":"unaffected","lessThanOrEqual":"5.10.*","versionType":"semver"},{"version":"5.15.216","status":"unaffected","lessThanOrEqual":"5.15.*","versionType":"semver"},{"version":"6.1.183","status":"unaffected","lessThanOrEqual":"6.1.*","versionType":"semver"},{"version":"6.6.151","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.103","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.44","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"7.1.8","status":"unaffected","lessThanOrEqual":"7.1.*","versionType":"semver"},{"version":"7.2","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["mm/huge_memory.c"]}],"references":[{"url":"https://git.kernel.org/stable/c/bc2f5eabaaf60ec18da70b619a8fba1bfb7dea3a"},{"url":"https://git.kernel.org/stable/c/f87c08060818ebb19bafed37c38244538da25097"},{"url":"https://git.kernel.org/stable/c/6f5c272d71845a669e4c8ee5c72b376e29a0e6e5"},{"url":"https://git.kernel.org/stable/c/be106f7855f03d3128ed0ce70ba74b484a90b473"},{"url":"https://git.kernel.org/stable/c/e3dd774dbfd0b5bc2dbd0995221751b1234f8205"},{"url":"https://git.kernel.org/stable/c/10065fb891651d9541e7a5a2db84c1e656ece4f9"},{"url":"https://git.kernel.org/stable/c/d640efe94d86d3be893d4c19220362546a637e90"},{"url":"https://git.kernel.org/stable/c/e923bd21058ea02fd0dcd3549d151d143fd036e5"}],"metrics":[{"cvssV3_1":{"version":"3.1","vectorString":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H","baseScore":7.8,"baseSeverity":"HIGH"},"scenarios":[{"lang":"en","value":"AV:L - The UAF is in __folio_split() on the memory_failure()->try_to_split_thp_page() path while splitting file-backed shmem THPs; reachability is via local syscalls (memfd/mmap/madvise/ftruncate) or admin hwpoison injection, not network or physical interfaces.\nAC:L - An attacker can deterministically create a shmem THP with tail pages beyond EOF and race MADV_HWPOISON-driven memory_failure() against concurrent truncate/close(iput) using attacker-controlled threads; both sides of the race are attacker-driven.\nPR:L - Reliable exploitation uses MADV_HWPOISON to invoke memory_failure() on a chosen tail page; CAP_SYS_ADMIN is available to user-namespace/container root, and the shmem THP setup needs only ordinary local mapping and truncation privileges.\nUI:N - No separate victim action is required; the attacker creates, maps, poisons, and truncates their own memfd/shmem/tmpfs object to reach the vulnerable split path.\nS:U - Impact is a kernel slab use-after-free on inode/mapping metadata in core MM within the same kernel security domain, not a VM escape, sandbox breakout, or other cross-authority boundary violation.\nC:H - KASAN reports slab-use-after-free in i_mmap_unlock_read() after shmem_free_in_core_inode() RCU-frees the inode; this inode/mapping UAF can be heap-sprayed into an arbitrary kernel memory read primitive.\nI:H - The same UAF corrupts freed inode slab objects and i_mmap_rwsem state, enabling heap grooming for arbitrary kernel writes and potential privilege escalation via control-flow hijacking per kernel UAF guidance.\nA:H - The use-after-free provokes a KASAN BUG/oops during i_mmap_unlock_read() and corrupts core MM inode state, capable of kernel panic or hang when triggered on production shmem/tmpfs workloads."}]}],"providerMetadata":{"shortName":"Linux","orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateUpdated":"2026-08-19T16:37:38.544Z"},"cpeApplicability":[{"nodes":[{"operator":"OR","negate":false,"cpeMatch":[{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"4.8","versionEndExcluding":"5.10.265"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"4.8","versionEndExcluding":"5.15.216"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"4.8","versionEndExcluding":"6.1.183"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"4.8","versionEndExcluding":"6.6.151"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"4.8","versionEndExcluding":"6.12.103"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"4.8","versionEndExcluding":"6.18.44"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"4.8","versionEndExcluding":"7.1.8"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"4.8","versionEndExcluding":"7.2"}]}]}],"x_generator":{"engine":"bippy-1.2.0"}},"adp":[{"title":"CISA ADP Vulnrichment","metrics":[{"other":{"type":"ssvc","content":{"id":"CVE-2026-74482","role":"CISA Coordinator","options":[{"Exploitation":"none"},{"Automatable":"no"},{"Technical Impact":"total"}],"version":"2.0.3","timestamp":"2026-10-16T18:57:49.050841Z"}}}],"providerMetadata":{"shortName":"CISA-ADP","orgId":"134c704f-9b21-4f2e-91b3-4a467353bcc0","dateUpdated":"2026-10-16T19:05:49.129Z"}}]}}}