CVE-2026-74482

Status: UPDATED  |  Advisory ID: CVE-2026-74482

Key Details

Affected Products, Subsystems & Sectors

What to Know

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. (NVD)

What to Do

Monitor Linux's web page for any future patch releases.

References