f2fs: bound the SIT/NAT bitmaps by the checkpoint pack

sit_ver_bitmap_bytesize and nat_ver_bitmap_bytesize are used as memcpy
lengths into and out of sbi->ckpt, which is sized from cp_payload alone,
and nothing compares either length against that allocation.

sanity_check_ckpt() has checked these two fields since c77ec61ca0a4, which
added them after a crafted image overran build_sit_info(). That check ties
each length to a segment count; it never compares either against the
allocation, which is the half this adds.

Mounting over-reads in build_sit_info() and build_node_manager(), and the
first checkpoint writes the same lengths back through the same pointers,
so the over-read's contents reach the on-disk checkpoint. An unmount is
enough; the filesystem does not have to be used.

Bound both ends the way __bitmap_ptr() lays them out. The three branches
differ, so a single sum of the two lengths would still admit a small
overflow when cp_payload is non-zero.

Fixes: 39a53e0ce0df ("f2fs: add superblock and major in-memory structure")
Cc: stable@kernel.org
Signed-off-by: Kaixuan Li <kaixuanli0131@gmail.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

0 files changed, 0 insertions, 0 deletions