In the Linux kernel, the following vulnerability has been resolved:
ocfs2: avoid moving extents to occupied clusters
For non-auto OCFS2_IOC_MOVE_EXT operations, userspace supplies a physical
me_goal. ocfs2_move_extent() initializes new_phys_cpos from that goal and
expects ocfs2_probe_alloc_group() to replace it with a free run in the
target block group.
The probe currently leaves *phys_cpos unchanged if the scan reaches the
end of the group without finding a free run. An occupied goal at the last
bit can therefore survive the probe and be passed to
__ocfs2_move_extent(), which copies file data into a cluster still owned
by another inode before the bitmap is updated.
When the probe does find a free run, it also subtracts move_len from the
ending bit. The start of an N-bit run ending at i is i – N + 1, so the
current calculation can report the bit immediately before the free run.
Clear *phys_cpos before scanning and use the correct free-run start.
Callers already treat a zero result as -ENOSPC, so failed probes no longer
continue with an occupied caller-controlled goal.
