CVE-2026-68442

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

btrfs: dont propagate EXTENT_FLAG_LOGGING to split extent maps

When btrfs_drop_extent_map_range() splits an extent map, the new split maps inherit the original maps flags through a local flags variable. Commit f86f7a75e2fb (btrfs: use the flags of an extent map to identify the compression type) changed the EXTENT_FLAG_LOGGING clearing to operate on em->flags instead of that local flags copy, so a split of an extent map that is currently being logged wrongly inherits EXTENT_FLAG_LOGGING.

The flag is then never cleared on the split, and when it is freed while still on the inodes modified_extents list (for example by the extent map shrinker) it trips the WARN_ON(!list_empty(&em->list)) in btrfs_free_extent_map() and leads to a use-after-free.

Clear EXTENT_FLAG_LOGGING from the local flags copy used for the splits and only clear EXTENT_FLAG_PINNED from em->flags, restoring the behaviour prior to f86f7a75e2fb.

Weakness

The product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory “belongs” to the code that operates on the new pointer.

Affected Software

Potential Mitigations

References

• https://git.kernel.org/stable/c/0e465c63f103a5ce6849614d6bda048d70eebec8
• https://git.kernel.org/stable/c/2a9246a424f45f33a1b8367052611ebe874868ad
• https://git.kernel.org/stable/c/5eff4d5b17fa1950e80bfd1ba43dc0699e61a644
• https://git.kernel.org/stable/c/9304713b70e7e1450e3a76e758836fe5391bfa95