CVE-2026-68442

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

btrfs: don't propagate EXTENTFLAGLOGGING to split extent maps

When btrfsdropextentmaprange() 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 EXTENTFLAGLOGGING 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 EXTENTFLAGLOGGING.

The flag is then never cleared on the split, and when it is freed while still on the inode's modifiedextents list (for example by the extent map shrinker) it trips the WARNON(!listempty(&em->list)) in btrfsfreeextentmap() and leads to a use-after-free.

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