In the Linux kernel, the following vulnerability has been resolved: btrfs: fix race between ordered extent completion and fiemap For fiemap we recently stopped locking the target extent range for the whole duration of the fiemap call, in order to avoid a deadlock in a scenario where the fiemap buffer happens to be a memory mapped range of the same file. This use case is very unlikely to be useful in practice but it may be triggered by fuzz testing (syzbot, etc). However by not locking the target extent range for the whole duration of the fiemap call we can race with an ordered extent. This happens like this: 1) The fiemap task finishes processing a file extent item that covers the file range [512K, 1M[, and that file extent item is the last item in the leaf currently being processed; 2) And ordered extent for the file range [768K, 2M[, in COW mode, completes (btrfs_finish_one_ordered()) and the file extent item covering the range [512K, 1M[ is trimmed to cover the ran…