Vulnerability CVE-2024-26704
Published: 2024-04-03

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

ext4: fix double-free of blocks due to wrong extents moved_len

In ext4_move_extents(), moved_len is only updated when all moves are
successfully executed, and only discards orig_inode and donor_inode
preallocations when moved_len is not zero. When the loop fails to exit
after successfully moving some extents, moved_len is not updated and
remains at 0, so it does not discard the preallocations.

If the moved extents overlap with the preallocated extents, the
overlapped extents are freed twice in ext4_mb_release_inode_pa() and
ext4_process_freed_data() (as described in commit 94d7c16cbbbd ("ext4:
Fix double-free of blocks with EXT4_IOC_MOVE_EXT")), and bb_free is
incremented twice. Hence when trim is executed, a zero-division bug is
triggered in mb_update_avg_fragment_size() because bb_free is not zero
and bb_fragments is zero.

Therefore, update move_len after each extent move to avoid the issue.

 References:
https://git.kernel.org/stable/c/b4fbb89d722cbb16beaaea234b7230faaaf68c71
https://git.kernel.org/stable/c/afbcad9ae7d6d11608399188f03a837451b6b3a1
https://git.kernel.org/stable/c/d033a555d9a1cf53dbf3301af7199cc4a4c8f537
https://git.kernel.org/stable/c/afba9d11320dad5ce222ac8964caf64b7b4bedb1
https://git.kernel.org/stable/c/185eab30486ba3e7bf8b9c2e049c79a06ffd2bc1
https://git.kernel.org/stable/c/2883940b19c38d5884c8626483811acf4d7e148f
https://git.kernel.org/stable/c/559ddacb90da1d8786dd8ec4fd76bbfa404eaef6
https://git.kernel.org/stable/c/55583e899a5357308274601364741a83e78d6ac4
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