# CVE-2025-38626: f2fs: fix to trigger foreground gc during f2fs_map_blocks() in lfs mode

CVE-2025-38626 is fixed in linux on 1 platform, first by DEBIAN-CVE-2025-38626, released August 22, 2025. It is not reported as exploited. Patch Radar priority: Routine.

- Web page: https://patchblox.com/security/cve/CVE-2025-38626
- Priority: Routine
- CVSS: 5.5 (Moderate)
- EPSS: 0.0017
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Aug 22, 2025
- Vendor advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2025-38626

## Description

In the Linux kernel, the following vulnerability has been resolved:  f2fs: fix to trigger foreground gc during f2fs_map_blocks() in lfs mode  w/ "mode=lfs" mount option, generic/299 will cause system panic as below:  ------------[ cut here ]------------ kernel BUG at fs/f2fs/segment.c:2835! Call Trace:  <TASK>  f2fs_allocate_data_block+0x6f4/0xc50  f2fs_map_blocks+0x970/0x1550  f2fs_iomap_begin+0xb2/0x1e0  iomap_iter+0x1d6/0x430  __iomap_dio_rw+0x208/0x9a0  f2fs_file_write_iter+0x6b3/0xfa0  aio_write+0x15d/0x2e0  io_submit_one+0x55e/0xab0  __x64_sys_io_submit+0xa5/0x230  do_syscall_64+0x84/0x2f0  entry_SYSCALL_64_after_hwframe+0x76/0x7e RIP: 0010:new_curseg+0x70f/0x720  The root cause of we run out-of-space is: in f2fs_map_blocks(), f2fs may trigger foreground gc only if it allocates any physical block, it will be a little bit later when there is multiple threads writing data w/ aio/dio/bufio method in parallel, since we always use OPU in lfs mode, so f2fs_map_blocks() does block allocations aggressively.  In order to fix this issue, let's give a chance to trigger foreground gc in prior to block allocation in f2fs_map_blocks().

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | linux Debian 12.15 (bookworm) | 6.1.170-1 | [DEBIAN-CVE-2025-38626](https://patchblox.com/security/data/fix/linux/debian-cve-2025-38626.md) | Aug 22, 2025 |
| Linux | linux Debian 13.5 (trixie) | 6.12.43-1 | [DEBIAN-CVE-2025-38626](https://patchblox.com/security/data/fix/linux/debian-cve-2025-38626.md) | Aug 22, 2025 |
| Linux | linux Debian 14 | 6.16.3-1 | [DEBIAN-CVE-2025-38626](https://patchblox.com/security/data/fix/linux/debian-cve-2025-38626.md) | Aug 22, 2025 |

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Data as of 2026-11-09T01:18:40Z UTC. Source: Patchblox Patch Radar (https://patchblox.com/security/patch-radar). Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo

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