linux-ext4 - Re: [PATCH v2 1/3] ext4: avoid potential buffer over-read in parse_apply_sb_mount

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Message-ID: <20250918165533.GF8084@frogsfrogsfrogs>
Date: Thu, 18 Sep 2025 09:55:33 -0700
From: "Darrick J. Wong" <djwong@...nel.org>
To: Jan Kara <jack@...e.cz>
Cc: tytso@....edu, linux-ext4@...r.kernel.org, linux-api@...r.kernel.org,
	stable@...r.kernel.org
Subject: Re: [PATCH v2 1/3] ext4: avoid potential buffer over-read in
 parse_apply_sb_mount_options()

On Wed, Sep 17, 2025 at 06:05:06PM +0200, Jan Kara wrote:
> On Tue 16-09-25 23:22:47, Theodore Ts'o via B4 Relay wrote:
> > From: Theodore Ts'o <tytso@....edu>
> > 
> > Unlike other strings in the ext4 superblock, we rely on tune2fs to
> > make sure s_mount_opts is NUL terminated.  Harden
> > parse_apply_sb_mount_options() by treating s_mount_opts as a potential
> > __nonstring.
> > 
> > Cc: stable@...r.kernel.org
> > Fixes: 8b67f04ab9de ("ext4: Add mount options in superblock")
> > Signed-off-by: Theodore Ts'o <tytso@....edu>
> 
> Looks good. Feel free to add:
> 
> Reviewed-by: Jan Kara <jack@...e.cz>

Looks fine to me too,
Reviewed-by: "Darrick J. Wong" <djwong@...nel.org>

--D

> 
> 								Honza
> 
> > ---
> >  fs/ext4/super.c | 17 +++++------------
> >  1 file changed, 5 insertions(+), 12 deletions(-)
> > 
> > diff --git a/fs/ext4/super.c b/fs/ext4/super.c
> > index 699c15db28a82f26809bf68533454a242596f0fd..94c98446c84f9a4614971d246ca7f001de610a8a 100644
> > --- a/fs/ext4/super.c
> > +++ b/fs/ext4/super.c
> > @@ -2460,7 +2460,7 @@ static int parse_apply_sb_mount_options(struct super_block *sb,
> >  					struct ext4_fs_context *m_ctx)
> >  {
> >  	struct ext4_sb_info *sbi = EXT4_SB(sb);
> > -	char *s_mount_opts = NULL;
> > +	char s_mount_opts[65];
> >  	struct ext4_fs_context *s_ctx = NULL;
> >  	struct fs_context *fc = NULL;
> >  	int ret = -ENOMEM;
> > @@ -2468,15 +2468,11 @@ static int parse_apply_sb_mount_options(struct super_block *sb,
> >  	if (!sbi->s_es->s_mount_opts[0])
> >  		return 0;
> >  
> > -	s_mount_opts = kstrndup(sbi->s_es->s_mount_opts,
> > -				sizeof(sbi->s_es->s_mount_opts),
> > -				GFP_KERNEL);
> > -	if (!s_mount_opts)
> > -		return ret;
> > +	strscpy_pad(s_mount_opts, sbi->s_es->s_mount_opts);
> >  
> >  	fc = kzalloc(sizeof(struct fs_context), GFP_KERNEL);
> >  	if (!fc)
> > -		goto out_free;
> > +		return -ENOMEM;
> >  
> >  	s_ctx = kzalloc(sizeof(struct ext4_fs_context), GFP_KERNEL);
> >  	if (!s_ctx)
> > @@ -2508,11 +2504,8 @@ static int parse_apply_sb_mount_options(struct super_block *sb,
> >  	ret = 0;
> >  
> >  out_free:
> > -	if (fc) {
> > -		ext4_fc_free(fc);
> > -		kfree(fc);
> > -	}
> > -	kfree(s_mount_opts);
> > +	ext4_fc_free(fc);
> > +	kfree(fc);
> >  	return ret;
> >  }
> >  
> > 
> > -- 
> > 2.51.0
> > 
> > 
> > 
> -- 
> Jan Kara <jack@...e.com>
> SUSE Labs, CR
>