CVE-2026-31702
Received
Received - Intake
Use-After-Free in Linux Kernel F2FS
Publication date: 2026-05-01
Last updated on: 2026-06-01
Assigner: kernel.org
Description
Description
In the Linux kernel, the following vulnerability has been resolved:
f2fs: fix use-after-free of sbi in f2fs_compress_write_end_io()
In f2fs_compress_write_end_io(), dec_page_count(sbi, type) can bring
the F2FS_WB_CP_DATA counter to zero, unblocking
f2fs_wait_on_all_pages() in f2fs_put_super() on a concurrent unmount
CPU. The unmount path then proceeds to call
f2fs_destroy_page_array_cache(sbi), which destroys
sbi->page_array_slab via kmem_cache_destroy(), and eventually
kfree(sbi). Meanwhile, the bio completion callback is still executing:
when it reaches page_array_free(sbi, ...), it dereferences
sbi->page_array_slab — a destroyed slab cache — to call
kmem_cache_free(), causing a use-after-free.
This is the same class of bug as CVE-2026-23234 (which fixed the
equivalent race in f2fs_write_end_io() in data.c), but in the
compressed writeback completion path that was not covered by that fix.
Fix this by moving dec_page_count() to after page_array_free(), so
that all sbi accesses complete before the counter decrement that can
unblock unmount. For non-last folios (where atomic_dec_return on
cic->pending_pages is nonzero), dec_page_count is called immediately
before returning — page_array_free is not reached on this path, so
there is no post-decrement sbi access. For the last folio,
page_array_free runs while the F2FS_WB_CP_DATA counter is still
nonzero (this folio has not yet decremented it), keeping sbi alive,
and dec_page_count runs as the final operation.
CVSS Scores
EPSS Scores
| Probability: | |
| Percentile: |
Meta Information
Affected Vendors & Products
| Vendor | Product | Version / Range |
|---|---|---|
| linux | linux_kernel | From 6.7 (inc) to 6.12.84 (exc) |
| linux | linux_kernel | 7.1 |
| linux | linux_kernel | 7.1 |
| linux | linux_kernel | From 6.13 (inc) to 6.18.25 (exc) |
| linux | linux_kernel | From 6.19 (inc) to 7.0.2 (exc) |
| linux | linux_kernel | From 5.6 (inc) to 6.6.136 (exc) |
Helpful Resources
Exploitability
CWE
KEV
| CWE ID | Description |
|---|---|
| CWE-416 | The product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory "belongs" to the code that operates on the new pointer. |
