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CVE-2024-26685: nilfs2: fix potential bug in end_buffer_async_write

• Severity: medium (CVSS 5.5 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.3% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2024-04-03 · updated 2026-06-17
• Weakness: CWE-787

Description

In the Linux kernel, the following vulnerability has been resolved: nilfs2: fix potential bug in end_buffer_async_write According to a syzbot report, end_buffer_async_write(), which handles the completion of block device writes, may detect abnormal condition of the buffer async_write flag and cause a BUG_ON failure when using nilfs2. Nilfs2 itself does not use end_buffer_async_write(). But, the async_write flag is now used as a marker by commit 7f42ec394156 ("nilfs2: fix issue with race condition of competition between segments for dirty blocks") as a means of resolving double list insertion of dirty blocks in nilfs_lookup_dirty_data_buffers() and nilfs_lookup_node_buffers() and the resulting crash. This modification is safe as long as it is used for file data and b-tree node blocks where the page caches are independent. However, it was irrelevant and redundant to also introduce async_write for segment summary and super root blocks that share buffers with the backing device. This led to the possibility that the BUG_ON check in end_buffer_async_write would fail as described above, if independent writebacks of the backing device occurred in parallel. The use of async_write for segment summary buffers has already been removed in a previous change. Fix this issue by removing the manipulation of the async_write flag for the remaining super root block buffer.

Affected products

• Debian Linux: 10.0
• Linux kernel: from 3.2.52 before 3.3; from 3.4.83 before 3.5; from 3.10.16 before 3.11; from 3.11.5 before 4.19.307; from 4.20 before 5.4.269; from 5.5 before 5.10.210 — fixed in 3.11, 3.3, 3.5, 4.19.307, 5.10.210, 5.15.149

How to fix

Upgrade to a fixed version: Linux kernel 3.11, 3.3, 3.5, 4.19.307. Check the vendor advisory for mitigations.

References

• https://git.kernel.org/stable/c/2c3bdba00283a6c7a5b19481a59a730f46063803
• https://git.kernel.org/stable/c/5bc09b397cbf1221f8a8aacb1152650c9195b02b
• https://git.kernel.org/stable/c/626daab3811b772086aef1bf8eed3ffe6f523eff
• https://git.kernel.org/stable/c/6589f0f72f8edd1fa11adce4eedbd3615f2e78ab
• https://git.kernel.org/stable/c/8fa90634ec3e9cc50f42dd605eec60f2d146ced8
• https://git.kernel.org/stable/c/c4a09fdac625e64abe478dcf88bfa20406616928
• https://git.kernel.org/stable/c/d31c8721e816eff5ca6573cc487754f357c093cd
• https://git.kernel.org/stable/c/f3e4963566f58726d3265a727116a42b591f6596
• https://git.kernel.org/stable/c/2c3bdba00283a6c7a5b19481a59a730f46063803
• https://git.kernel.org/stable/c/5bc09b397cbf1221f8a8aacb1152650c9195b02b
• https://git.kernel.org/stable/c/626daab3811b772086aef1bf8eed3ffe6f523eff
• https://git.kernel.org/stable/c/6589f0f72f8edd1fa11adce4eedbd3615f2e78ab

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