CVE-2025-39800

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

btrfs: abort transaction on unexpected eb generation at btrfs_copy_root()

If we find an unexpected generation for the extent buffer we are cloning
at btrfs_copy_root(), we just WARN_ON() and don't error out and abort the
transaction, meaning we allow to persist metadata with an unexpected
generation. Instead of warning only, abort the transaction and return
-EUCLEAN.