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

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Date: Tue, 4 Jun 2024 09:17:17 +0800
From: Lizhi Xu <lizhi.xu@...driver.com>
To: <krisman@...e.de>
CC: <adilger.kernel@...ger.ca>, <coreteam@...filter.org>,
        <davem@...emloft.net>, <ebiggers@...nel.org>, <fw@...len.de>,
        <jaegeuk@...nel.org>, <kadlec@...filter.org>, <kuba@...nel.org>,
        <linux-ext4@...r.kernel.org>, <linux-fscrypt@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <lizhi.xu@...driver.com>,
        <lkp@...el.com>, <llvm@...ts.linux.dev>, <netdev@...r.kernel.org>,
        <netfilter-devel@...r.kernel.org>, <oe-kbuild-all@...ts.linux.dev>,
        <pablo@...filter.org>,
        <syzbot+340581ba9dceb7e06fb3@...kaller.appspotmail.com>,
        <syzkaller-bugs@...glegroups.com>, <tytso@....edu>
Subject: Re: [PATCH V5] ext4: check hash version and filesystem casefolded consistent

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@...kaller.appspotmail.com
> > Signed-off-by: Lizhi Xu <lizhi.xu@...driver.com>
> > ---
> >  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().
> 
> 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.

Lizhi