Re: [PATCH V5] ext4: check hash version and filesystem casefolded consistent

[Gabriel Krisman Bertazi]

Lizhi Xu <lizhi.xu@xxxxxxxxxxxxx> writes:

> On Mon, 03 Jun 2024 10:50:51 -0400, Gabriel Krisman Bertazi wrote:
>> > When mounting the ext4 filesystem, if the hash version and casefolded are not
>> > consistent, exit the mounting.
>> >
>> > Reported-by: syzbot+340581ba9dceb7e06fb3@xxxxxxxxxxxxxxxxxxxxxxxxx
>> > Signed-off-by: Lizhi Xu <lizhi.xu@xxxxxxxxxxxxx>
>> > ---
>> >  fs/ext4/super.c | 5 +++++
>> >  1 file changed, 5 insertions(+)
>> >
>> > diff --git a/fs/ext4/super.c b/fs/ext4/super.c
>> > index c682fb927b64..0ad326504c50 100644
>> > --- a/fs/ext4/super.c
>> > +++ b/fs/ext4/super.c
>> > @@ -5262,6 +5262,11 @@ static int __ext4_fill_super(struct fs_context *fc, struct super_block *sb)
>> >  		goto failed_mount;
>> >  
>> >  	ext4_hash_info_init(sb);
>> > +	if (es->s_def_hash_version == DX_HASH_SIPHASH && 
>> > +	    !ext4_has_feature_casefold(sb)) {
>> 
>> Can we ever have DX_HASH_SIPHASH set up in the super block?  I thought
>> it was used solely for directories where ext4_hash_in_dirent(inode) is
>> true.
> The value of s'def_hash_version is obtained by reading the super block from the
> buffer cache of the block device in ext4_load_super().

Yes, I know.  My point is whether this check should just be:

if (es->s_def_hash_version == DX_HASH_SIPHASH)
	goto failed_mount;

Since, IIUC, DX_HASH_SIPHASH is done per-directory and not written to
the sb.

>> If this is only for the case of a superblock corruption, perhaps we
>> should always reject the mount, whether casefold is enabled or not?
> Based on the existing information, it cannot be confirmed whether the superblock
> is corrupt, but one thing is clear: if the default hash version of the superblock
> is set to DX_HASH_SIPHASH, but the casefold feature is not set at the same time,
> it is definitely an error.


-- 
Gabriel Krisman Bertazi