[PATCH 5.17 643/772] ext4: filter out EXT4_FC_REPLAY from on-disk superblock field s_state

Greg Kroah-Hartman
2022-06-07T21:39:29Z

From: Theodore Ts'o <tytso@mit.edu>

commit c878bea3c9d724ddfa05a813f30de3d25a0ba83f upstream.

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
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
fs/ext4/super.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)

--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -4874,7 +4874,7 @@ static int __ext4_fill_super(struct fs_c
sbi->s_inodes_per_block;
sbi->s_desc_per_block = blocksize / EXT4_DESC_SIZE(sb);
sbi->s_sbh = bh;
- sbi->s_mount_state = le16_to_cpu(es->s_state);
+ sbi->s_mount_state = le16_to_cpu(es->s_state) & ~EXT4_FC_REPLAY;
sbi->s_addr_per_block_bits = ilog2(EXT4_ADDR_PER_BLOCK(sb));
sbi->s_desc_per_block_bits = ilog2(EXT4_DESC_PER_BLOCK(sb));

@@ -6437,7 +6437,8 @@ static int __ext4_remount(struct fs_cont
if (err)
goto restore_opts;
}
- sbi->s_mount_state = le16_to_cpu(es->s_state);
+ sbi->s_mount_state = (le16_to_cpu(es->s_state) &
+ ~EXT4_FC_REPLAY);

err = ext4_setup_super(sb, es, 0);
if (err)