CVE-2026-74482 (GCVE-0-2026-74482)
Vulnerability from cvelistv5
Published
2026-08-15 12:27
Modified
2026-08-19 16:37
Severity ?
VLAI Severity ?
EPSS score ?
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.
References
Impacted products
| Vendor | Product | Version | ||
|---|---|---|---|---|
| Linux | Linux |
Version: baa355fd331424526e742d41d9b90d5f9d10f716 Version: baa355fd331424526e742d41d9b90d5f9d10f716 Version: baa355fd331424526e742d41d9b90d5f9d10f716 Version: baa355fd331424526e742d41d9b90d5f9d10f716 Version: baa355fd331424526e742d41d9b90d5f9d10f716 Version: baa355fd331424526e742d41d9b90d5f9d10f716 Version: baa355fd331424526e742d41d9b90d5f9d10f716 Version: baa355fd331424526e742d41d9b90d5f9d10f716 |
||
{
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{
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{
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{
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"negate": false,
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"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-\u003ehost) 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\u0027s @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."
}
],
"metrics": [
{
"cvssV3_1": {
"baseScore": 7.8,
"baseSeverity": "HIGH",
"vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
"version": "3.1"
},
"scenarios": [
{
"lang": "en",
"value": "AV:L - The UAF is in __folio_split() on the memory_failure()-\u003etry_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": {
"dateUpdated": "2026-08-19T16:37:38.544Z",
"orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"shortName": "Linux"
},
"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"
}
],
"title": "mm/huge_memory: unlock i_mmap_rwsem before releasing after-split folios",
"x_generator": {
"engine": "bippy-1.2.0"
}
}
},
"cveMetadata": {
"assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"assignerShortName": "Linux",
"cveId": "CVE-2026-74482",
"datePublished": "2026-08-15T12:27:15.083Z",
"dateReserved": "2026-08-15T05:44:03.904Z",
"dateUpdated": "2026-08-19T16:37:38.544Z",
"state": "PUBLISHED"
},
"dataType": "CVE_RECORD",
"dataVersion": "5.2"
}
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Sightings
| Author | Source | Type | Date |
|---|
Nomenclature
- Seen: The vulnerability was mentioned, discussed, or seen somewhere by the user.
- Confirmed: The vulnerability is confirmed from an analyst perspective.
- Published Proof of Concept: A public proof of concept is available for this vulnerability.
- Exploited: This vulnerability was exploited and seen by the user reporting the sighting.
- Patched: This vulnerability was successfully patched by the user reporting the sighting.
- Not exploited: This vulnerability was not exploited or seen by the user reporting the sighting.
- Not confirmed: The user expresses doubt about the veracity of the vulnerability.
- Not patched: This vulnerability was not successfully patched by the user reporting the sighting.
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