Linux Kernel F2FS move_data_block/folio_put race condition

Summaryinfo

A vulnerability marked as problematic has been reported in Linux Kernel. Affected is the function move_data_block/folio_put of the component F2FS. The manipulation leads to race condition. This vulnerability is traded as CVE-2026-63813. An attack has to be approached locally. There is no exploit available.

Detailsinfo

A vulnerability was found in Linux Kernel (the affected version is unknown) and classified as problematic. This issue affects the function move_data_block/folio_put of the component F2FS. The manipulation with an unknown input leads to a race condition vulnerability. Using CWE to declare the problem leads to CWE-362. The product contains a code sequence that can run concurrently with other code, and the code sequence requires temporary, exclusive access to a shared resource, but a timing window exists in which the shared resource can be modified by another code sequence that is operating concurrently. Impacted is integrity, and availability. The summary by CVE is:

In the Linux kernel, the following vulnerability has been resolved: Revert "f2fs: remove non-uptodate folio from the page cache in move_data_block" This reverts commit 9609dd704725a40cd63d915f2ab6c44248a44598. The kernel panics are keeping to be reported especially when the f2fs partition get almost full. By investigation, we find that the reason is one f2fs page got freed to buddy without being deleted from LRU and the root cause is the race happened in [2] which is enrolled by this commit. There are 3 race processes in this scenario, please find below for their main activities. The changed code in move_data_block() lets the GC path evict the tail-end folio from the page cache through folio_end_dropbehind(). Once folio_unmap_invalidate() removes the folio from mapping->i_pages, the page-cache references for all pages in the folio are dropped. The folio is then kept alive only by temporary external references, which allows a later split to operate on a folio whose subpages are no longer protected by page-cache references. After the page-cache references are gone, split_folio_to_order() can split the big folio into individual pages and put the resulting subpages back on the LRU. For tail pages beyond EOF, split removes them from the page cache and drops their page-cache references. A tail page can then remain on the LRU with PG_lru set while holding only the split caller's temporary reference. When free_folio_and_swap_cache() drops that final reference, the page enters the final folio_put() release path. In parallel, folio_isolate_lru() can observe the same tail page with a non-zero refcount and PG_lru set. It clears PG_lru before taking its own reference. If this races with the final folio_put() from the split path, __folio_put() sees PG_lru already cleared and skips lruvec_del_folio(). The page is then freed back to the allocator while its lru links are still present in the LRU list. A later LRU operation on a neighboring page detects the stale link and reports list corruption. [1] [ 22.486082] list_del corruption. next->prev should be fffffffec10e0ac8, but was dead000000000122. (next=fffffffec10e0a88) [ 22.486130] ------------[ cut here ]------------ [ 22.486134] kernel BUG at lib/list_debug.c:67! [ 22.486141] Internal error: Oops - BUG: 00000000f2000800 [#1] SMP [ 22.488502] Tainted: [W]=WARN, [O]=OOT_MODULE [ 22.488506] Hardware name: Spreadtrum UMS9230 1H10 SoC (DT) [ 22.488511] pstate: 604000c5 (nZCv daIF +PAN -UAO -TCO -DIT -SSBS BTYPE=--) [ 22.488517] pc : __list_del_entry_valid_or_report+0x14c/0x154 [ 22.488531] lr : __list_del_entry_valid_or_report+0x14c/0x154 [ 22.488539] sp : ffffffc08006b830 [ 22.488542] x29: ffffffc08006b868 x28: 0000000000003020 x27: 0000000000000000 [ 22.488553] x26: 0000000000000000 x25: 0000000000000004 x24: fffffffec10e0ac0 [ 22.488564] x23: 00000000000000e8 x22: 0000000000000024 x21: dead000000000122 [ 22.488574] x20: fffffffec10e0a88 x19: fffffffec10e0ac8 x18: ffffffc080061060 [ 22.488585] x17: 20747562202c3863 x16: 6130653031636566 x15: 0000000000000058 [ 22.488595] x14: 0000000000000004 x13: ffffff80f91e0000 x12: 0000000000000003 [ 22.488605] x11: 0000000000000003 x10: 0000000000000001 x9 : ffe85721f0e25f00 [ 22.488615] x8 : ffe85721f0e25f00 x7 : 0000000000000000 x6 : 6c65645f7473696c [ 22.488625] x5 : ffffffed39b23026 x4 : 0000000000000000 x3 : 0000000000000010 [ 22.488636] x2 : 0000000000000000 x1 : 0000000000000000 x0 : 000000000000006d [ 22.488647] Call trace: [ 22.488651] __list_del_entry_valid_or_report+0x14c/0x154 (P) [ 22.488661] __folio_put+0x2bc/0x434 [ 22.488670] folio_put+0x28/0x58 [ 22.488678] do_garbage_collect+0x1a34/0x2584 [ 22.488689] f2fs_gc+0x230/0x9b4 [ 22.488697] f2fs_fallocate+0xb90/0xdf4 [ 22.488706] vfs_fallocate+0x1b4/0x2bc [ 22.488716] __arm64_sys_fallocate+0x44/0x78 [ 22.488725] invoke_syscall+0x58/0xe4 [ 22.488732] do_el0_svc+0x48/0xdc [ 22.488739] el0 ---truncated---

The advisory is shared at git.kernel.org. The identification of this vulnerability is CVE-2026-63813 since 07/19/2026. The exploitation is known to be easy. An attack has to be approached locally. Technical details are known, but no exploit is available.

Applying the patch 9609dd704725a40cd63d915f2ab6c44248a44598 is able to eliminate this problem.

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Productinfo

Type

• Operating System

Vendor

• Linux

Name

• Kernel

License

• open-source

Website

• Vendor: https://www.kernel.org/

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Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

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