ext4: validate p_idx bounds in ext4_ext_correct_indexes

ext4_ext_correct_indexes() walks up the extent tree correcting
index entries when the first extent in a leaf is modified. Before
accessing path[k].p_idx->ei_block, there is no validation that
p_idx falls within the valid range of index entries for that
level.

If the on-disk extent header contains a corrupted or crafted
eh_entries value, p_idx can point past the end of the allocated
buffer, causing a slab-out-of-bounds read.

Fix this by validating path[k].p_idx against EXT_LAST_INDEX() at
both access sites: before the while loop and inside it. Return
-EFSCORRUPTED if the index pointer is out of range, consistent
with how other bounds violations are handled in the ext4 extent
tree code.

Reported-by: syzbot+04c4e65cab786a2e5b7e@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=04c4e65cab786a2e5b7e
Signed-off-by: Tejas Bharambe <tejas.bharambe@outlook.com>
Link: https://patch.msgid.link/JH0PR06MB66326016F9B6AD24097D232B897CA@JH0PR06MB6632.apcprd06.prod.outlook.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Cc: stable@kernel.org

0 files changed, 0 insertions, 0 deletions