linux-ext4 - Re: [PATCH v2] ext4: ext4_fill_super shouldn't return 0 on corruption

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Date:	Tue, 16 Nov 2010 14:55:38 -0800
From:	"Darrick J. Wong" <djwong@...ibm.com>
To:	Lukas Czerner <lczerner@...hat.com>
Cc:	Eric Sandeen <sandeen@...hat.com>, "Theodore Ts'o" <tytso@....edu>,
	"Patrick J. LoPresti" <lopresti@...il.com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	linux-ext4 <linux-ext4@...r.kernel.org>,
	Mingming Cao <mcao@...ibm.com>
Subject: Re: [PATCH v2] ext4: ext4_fill_super shouldn't return 0 on
	corruption

On Tue, Nov 16, 2010 at 01:56:31PM +0100, Lukas Czerner wrote:
> On Mon, 15 Nov 2010, Darrick J. Wong wrote:
> 
> > At the start of ext4_fill_super, ret is set to -EINVAL, and any failure path
> > out of that function returns ret.  However, the generic_check_addressable
> > clause sets ret = 0 (if it passes), which means that a subsequent failure (e.g.
> > a group checksum error) returns 0 even though the mount should fail.  This
> > causes vfs_kern_mount in turn to think that the mount succeeded, leading to an
> > oops.
> > 
> > A simple fix is to avoid using ret for the generic_check_addressable check,
> > which was last changed in commit 30ca22c70e3ef0a96ff84de69cd7e8561b416cb2.
> > 
> > v2: Return -EFBIG in the error case, per Eric Sandeen's suggestion.
> > 
> > Signed-off-by: Darrick J. Wong <djwong@...ibm.com>
> > ---
> > 
> >  fs/ext4/super.c |    6 +++---
> >  1 files changed, 3 insertions(+), 3 deletions(-)
> > 
> > diff --git a/fs/ext4/super.c b/fs/ext4/super.c
> > index 40131b7..120c034 100644
> > --- a/fs/ext4/super.c
> > +++ b/fs/ext4/super.c
> > @@ -3257,13 +3257,13 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
> >  	 * Test whether we have more sectors than will fit in sector_t,
> >  	 * and whether the max offset is addressable by the page cache.
> >  	 */
> > -	ret = generic_check_addressable(sb->s_blocksize_bits,
> > -					ext4_blocks_count(es));
> > -	if (ret) {
> > +	if (generic_check_addressable(sb->s_blocksize_bits,
> > +				      ext4_blocks_count(es))) {
> >  		ext4_msg(sb, KERN_ERR, "filesystem"
> >  			 " too large to mount safely on this system");
> >  		if (sizeof(sector_t) < 8)
> >  			ext4_msg(sb, KERN_WARNING, "CONFIG_LBDAF not enabled");
> > +		ret = -EFBIG;
> >  		goto failed_mount;
> >  	}
> >  
> > --
> > To unsubscribe from this list: send the line "unsubscribe linux-ext4" in
> > the body of a message to majordomo@...r.kernel.org
> > More majordomo info at  http://vger.kernel.org/majordomo-info.html
> > 
> 
> Hi,
> 
> the untested diff below seems like a more general solution to me,
> since it allows to return the actual error from
> generic_check_addressable().

It seems to work ok for me, so:

Acked-by: Darrick J. Wong <djwong@...ibm.com>

I will make the same change to ext3.

--D
> 
> Thanks.
> 
> -Lukas
> 
> 
> diff --git a/fs/ext4/super.c b/fs/ext4/super.c
> index 61182fe..3d89b72 100644
> --- a/fs/ext4/super.c
> +++ b/fs/ext4/super.c
> @@ -3268,13 +3268,14 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
>  	 * Test whether we have more sectors than will fit in sector_t,
>  	 * and whether the max offset is addressable by the page cache.
>  	 */
> -	ret = generic_check_addressable(sb->s_blocksize_bits,
> +	err = generic_check_addressable(sb->s_blocksize_bits,
>  					ext4_blocks_count(es));
> -	if (ret) {
> +	if (err) {
>  		ext4_msg(sb, KERN_ERR, "filesystem"
>  			 " too large to mount safely on this system");
>  		if (sizeof(sector_t) < 8)
>  			ext4_msg(sb, KERN_WARNING, "CONFIG_LBDAF not enabled");
> +		ret = err;
>  		goto failed_mount;
>  	}
> 
> --
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