# CVE-2025-40054

## Summary

- **CVE ID:** CVE-2025-40054
- **Severity:** HIGH
- **CVSS Score:** 7.8 (CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H)
- **CWE:** N/A
- **Published:** Oct 28, 2025
- **Last Modified:** Aug 23, 2026

## Description

In the Linux kernel, the following vulnerability has been resolved:

f2fs: fix UAF issue in f2fs_merge_page_bio()

As JY reported in bugzilla [1],

Unable to handle kernel NULL pointer dereference at virtual address 0000000000000000
pc : [0xffffffe51d249484] f2fs_is_cp_guaranteed+0x70/0x98
lr : [0xffffffe51d24adbc] f2fs_merge_page_bio+0x520/0x6d4
CPU: 3 UID: 0 PID: 6790 Comm: kworker/u16:3 Tainted: P    B   W  OE      6.12.30-android16-5-maybe-dirty-4k #1 5f7701c9cbf727d1eebe77c89bbbeb3371e895e5
Tainted: [P]=PROPRIETARY_MODULE, [B]=BAD_PAGE, [W]=WARN, [O]=OOT_MODULE, [E]=UNSIGNED_MODULE
Workqueue: writeback wb_workfn (flush-254:49)
Call trace:
 f2fs_is_cp_guaranteed+0x70/0x98
 f2fs_inplace_write_data+0x174/0x2f4
 f2fs_do_write_data_page+0x214/0x81c
 f2fs_write_single_data_page+0x28c/0x764
 f2fs_write_data_pages+0x78c/0xce4
 do_writepages+0xe8/0x2fc
 __writeback_single_inode+0x4c/0x4b4
 writeback_sb_inodes+0x314/0x540
 __writeback_inodes_wb+0xa4/0xf4
 wb_writeback+0x160/0x448
 wb_workfn+0x2f0/0x5dc
 process_scheduled_works+0x1c8/0x458
 worker_thread+0x334/0x3f0
 kthread+0x118/0x1ac
 ret_from_fork+0x10/0x20

[1] https://bugzilla.kernel.org/show_bug.cgi?id=220575

The panic was caused by UAF issue w/ below race condition:

kworker
- writepages
 - f2fs_write_cache_pages
  - f2fs_write_single_data_page
   - f2fs_do_write_data_page
    - f2fs_inplace_write_data
     - f2fs_merge_page_bio
      - add_inu_page
      : cache page #1 into bio & cache bio in
        io->bio_list
  - f2fs_write_single_data_page
   - f2fs_do_write_data_page
    - f2fs_inplace_write_data
     - f2fs_merge_page_bio
      - add_inu_page
      : cache page #2 into bio which is linked
        in io->bio_list
						write
						- f2fs_write_begin
						: write page #1
						 - f2fs_folio_wait_writeback
						  - f2fs_submit_merged_ipu_write
						   - f2fs_submit_write_bio
						   : submit bio which inclues page #1 and #2

						software IRQ
						- f2fs_write_end_io
						 - fscrypt_free_bounce_page
						 : freed bounced page which belongs to page #2
      - inc_page_count( , WB_DATA_TYPE(data_folio), false)
      : data_folio points to fio->encrypted_page
        the bounced page can be freed before
        accessing it in f2fs_is_cp_guarantee()

It can reproduce w/ below testcase:
Run below script in shell #1:
for ((i=1;i>0;i++)) do xfs_io -f /mnt/f2fs/enc/file \
-c "pwrite 0 32k" -c "fdatasync"

Run below script in shell #2:
for ((i=1;i>0;i++)) do xfs_io -f /mnt/f2fs/enc/file \
-c "pwrite 0 32k" -c "fdatasync"

So, in f2fs_merge_page_bio(), let's avoid using fio->encrypted_page after
commit page into internal ipu cache.

## Affected Products

- Linux — Linux (0b20fcec8651569935a10afe03fedc0b812d044e)
- Linux — Linux (5.5)
- Linux — Linux (0)
- Linux — Linux (6.17.3)
- Linux — Linux (6.18)
- Linux — Linux (5.10.266)
- Linux — Linux (5.15.217)
- Linux — Linux (6.1.184)
- Linux — Linux (6.6.153)
- Linux — Linux (6.12.105)

## References

- [CNA](https://git.kernel.org/stable/c/01118321e0c8a5f3ece57d0d377bfc92d83cd210)
- [CNA](https://git.kernel.org/stable/c/edf7e9040fc52c922db947f9c6c36f07377c52ea)
- [CNA](https://git.kernel.org/stable/c/1f7b44b4a2b2939f08b279cbb9e6b5dcb8ffea32)
- [CNA](https://git.kernel.org/stable/c/e193d8953647c8b575830852aa5ea0995b98d2b1)
- [CNA](https://git.kernel.org/stable/c/410337c2301ae78a081e1b5ebbe8ec374fef4cb6)
- [CNA](https://git.kernel.org/stable/c/68e094232dfe5027c4fd2dcded93d2d6800bae04)
- [CNA](https://git.kernel.org/stable/c/7dd611131d82d7fc4212b555eb1103160bdad302)

## Exploitation Prediction (EPSS)

- **EPSS Score:** 0.15%
- **EPSS Percentile:** 5.0

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_Exported from OnDuty AI Vulnerability Intelligence on 2026-09-18._