The EXT4_FC_REPLAY bit in sbi->s_mount_state is used to indicate that
we are in the middle of replay the fast commit journal. This was
actually a mistake, since the sbi->s_mount_info is initialized from
es->s_state. Arguably s_mount_state is misleadingly named, but the
name is historical --- s_mount_state and s_state dates back to ext2.
What should have been used is the ext4_{set,clear,test}_mount_flag()
inline functions, which sets EXT4_MF_* bits in sbi->s_mount_flags.
The problem with using EXT4_FC_REPLAY is that a maliciously corrupted
superblock could result in EXT4_FC_REPLAY getting set in
s_mount_state. This bypasses some sanity checks, and this can trigger
a BUG() in ext4_es_cache_extent(). As a easy-to-backport-fix, filter
out the EXT4_FC_REPLAY bit for now. We should eventually transition
away from EXT4_FC_REPLAY to something like EXT4_MF_REPLAY.
Cc: stable@kernel.org
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Link: https://lore.kernel.org/r/20220420192312.1655305-1-phind.uet@gmail.com
Link: https://lore.kernel.org/r/20220517174028.942119-1-tytso@mit.edu
Reported-by: syzbot+c7358a3cd05ee786eb31@syzkaller.appspotmail.com
c878bea3c9