On Mon, Feb 10, 2020 at 03:43:16PM +0100, Jan Kara wrote:
> DIR_INDEX has been introduced as a compat ext4 feature. That means that
> even kernels / tools that don't understand the feature may modify the
> filesystem. This works because for kernels not understanding indexed dir
> format, internal htree nodes appear just as empty directory entries.
> Index dir aware kernels then check the htree structure is still
> consistent before using the data. This all worked reasonably well until
> metadata checksums were introduced. The problem is that these
> effectively made DIR_INDEX only ro-compatible because internal htree
> nodes store checksums in a different place than normal directory blocks.
> Thus any modification ignorant to DIR_INDEX (or just clearing
> EXT4_INDEX_FL from the inode) will effectively cause checksum mismatch
> and trigger kernel errors. So we have to be more careful when dealing
> with indexed directories on filesystems with checksumming enabled.
>
> 1) We just disallow loading any directory inodes with EXT4_INDEX_FL when
> DIR_INDEX is not enabled. This is harsh but it should be very rare (it
> means someone disabled DIR_INDEX on existing filesystem and didn't run
> e2fsck), e2fsck can fix the problem, and we don't want to answer the
> difficult question: "Should we rather corrupt the directory more or
> should we ignore that DIR_INDEX feature is not set?"
>
> 2) When we find out htree structure is corrupted (but the filesystem and
> the directory should in support htrees), we continue just ignoring htree
> information for reading but we refuse to add new entries to the
> directory to avoid corrupting it more.
>
> CC: stable@xxxxxxxxxxxxxxx
> Fixes: dbe89444042a ("ext4: Calculate and verify checksums for htree nodes")
> Signed-off-by: Jan Kara <jack@xxxxxxx>
Applied, thanks.
- Ted
