GHSA-2666-8P4F-7R6X
Vulnerability from github – Published: 2026-08-15 15:30 – Updated: 2026-08-19 18:32In 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.
{
"affected": [],
"aliases": [
"CVE-2026-74482"
],
"database_specific": {
"cwe_ids": [],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2026-08-15T13:17:53Z",
"severity": "HIGH"
},
"details": "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.",
"id": "GHSA-2666-8p4f-7r6x",
"modified": "2026-08-19T18:32:28Z",
"published": "2026-08-15T15:30:34Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-74482"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/10065fb891651d9541e7a5a2db84c1e656ece4f9"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/6f5c272d71845a669e4c8ee5c72b376e29a0e6e5"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/bc2f5eabaaf60ec18da70b619a8fba1bfb7dea3a"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/be106f7855f03d3128ed0ce70ba74b484a90b473"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/d640efe94d86d3be893d4c19220362546a637e90"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/e3dd774dbfd0b5bc2dbd0995221751b1234f8205"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/e923bd21058ea02fd0dcd3549d151d143fd036e5"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/f87c08060818ebb19bafed37c38244538da25097"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
"type": "CVSS_V3"
}
]
}
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