Vulnerability CVE-2024-26685
Published: 2024-04-03

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.

 References:
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/8fa90634ec3e9cc50f42dd605eec60f2d146ced8
https://git.kernel.org/stable/c/6589f0f72f8edd1fa11adce4eedbd3615f2e78ab
https://git.kernel.org/stable/c/2c3bdba00283a6c7a5b19481a59a730f46063803
https://git.kernel.org/stable/c/626daab3811b772086aef1bf8eed3ffe6f523eff
https://git.kernel.org/stable/c/5bc09b397cbf1221f8a8aacb1152650c9195b02b
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