CVE-2026-68442btrfs: don't propagate EXTENT_FLAG_LOGGING to split extent maps

Official description

In the Linux kernel, the following vulnerability has been resolved: btrfs: don't 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 map's 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 inode's 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.

Affected packages & fixed versions

Affected products (as reported)

References

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