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.
| Vendor | Product | Versions |
|---|---|---|
| linux | linux_kernel | 4c8ff7095bef64fc47e996a938f7d57f9e077da3, 4c8ff7095bef64fc47e996a938f7d57f9e077da3, 4c8ff7095bef64fc47e996a938f7d57f9e077da3, 4c8ff7095bef64fc47e996a938f7d57f9e077da3, 4c8ff7095bef64fc47e996a938f7d57f9e077da3, 5.6, 6.6.135, 6.12.83, 6.18.24, 7.0.1 |
Downstream vendors/products affected by this vulnerability
| Vendor | Product | Source | Confidence |
|---|---|---|---|
| open source | open source linux kernel | cert_advisory | 90% |
Updated severity to CRITICAL, added new affected versions, and noted that no exploit is available.
Initial creation
