HIGH Introduced in 7.0
f2fs LargeFolio Race
CVE-2026-89836
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
KernelScan AI6.6MEDIUM
01Description
In the Linux kernel, the following vulnerability has been resolved: f2fs: fix folio_nr_pages() race after put in large folio invalidate Our v6.18 based Android system is continuely suffering livelock and bad page stat as shown in[1] which related to broken xarray slot status. By investigating big folio operations within f2fs, we find below races and fix it by get the nr_pages before drop the refcount and folio_lock. f2fs_get_read_data_folio() calls f2fs_folio_put() before folio_nr_pages() when invalidating a large folio from the page cache. That unlocks the folio and drops the caller reference, leaving a window where a concurrent truncate or folio split can shrink the compound folio or free it before the invalidate range is computed. An undersized range then leaves split sub-folios in mapping->i_pages, which can later interact badly with truncate and reclaim (stale xarray entries and bad page state when folio->mapping no longer matches the mapping being truncated). [1] PID: 2594 TASK: ffffff8169b81580 CPU: 7 COMMAND: "Thread-3" #0 [ffffffc08ef2b8a0] xas_load at ffffffe52d1f42a4 #1 [ffffffc08ef2b900] find_get_entries at ffffffe52c185798 #2 [ffffffc08ef2bb60] truncate_inode_pages_range at ffffffe52c19e83c #3 [ffffffc08ef2bbc0] truncate_inode_pages_final at ffffffe52c19ec2c #4 [ffffffc08ef2bc20] f2fs_evict_inode at ffffffe52c4c8400 #5 [ffffffc08ef2bcc0] evict at ffffffe52c2de9f4 #6 [ffffffc08ef2bd00] iput at ffffffe52c2db1b4 #7 [ffffffc08ef2bd30] dentry_unlink_inode at ffffffe52c2d7204 #8 [ffffffc08ef2bd50] __dentry_kill at ffffffe52c2d3dcc #9 [ffffffc08ef2bd80] dput at ffffffe52c2d3c3c #10 [ffffffc08ef2bda0] __fput at ffffffe52c2b0a7c #11 [ffffffc08ef2bde0] ____fput at ffffffe52c2b1034 #12 [ffffffc08ef2bdf0] task_work_run at ffffffe52beea200 #13 [ffffffc08ef2be20] exit_to_user_mode_loop at ffffffe52bfbc17c #14 [ffffffc08ef2be80] el0_svc at ffffffe52d1f8e54 #15 [ffffffc08ef2beb0] el0t_64_sync_handler at ffffffe52d1f8d10
02KernelScan AI Analysis
Risk summary
A race condition in f2fs large folio handling allows concurrent truncate or folio split operations to corrupt page cache state, leading to stale xarray entries, bad page statistics, and livelock. Any local user with read access to an f2fs filesystem supporting large folios can trigger this through normal file operations. The primary impact is denial of service through livelock and resource exhaustion, with potential for limited data corruption.
Vulnerability analysis
A race condition in the f2fs filesystem's handling of large memory pages can leave stale entries in the kernel's page tracking structures. When the filesystem invalidates a large page, it releases its hold on that page before calculating how many pages must be removed. This opens a window where another thread can shrink or free the page in the meantime, causing the removal to cover too small a range. Leftover sub-pages then cause system livelock and internal page-state errors during later cleanup. The fix calculates the page count before releasing the hold, so the removal always covers the full original range. Any local user with access to an f2fs filesystem that uses large pages can trigger this through ordinary file reads, with no special privileges needed.
Lifecycle
03Fix Versions
| Branch | Introduced | Fixed in | Patch commit |
|---|---|---|---|
| 7.2 | 7.0 | 7.2.5 | cc34df18da92 |
| mainline | 7.0 | 7.3 | 0dab71381f1b |