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

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Message-ID: <alpine.LFD.2.00.1011161351230.5515@dhcp-lab-213.englab.brq.redhat.com>
Date:	Tue, 16 Nov 2010 13:56:31 +0100 (CET)
From:	Lukas Czerner <lczerner@...hat.com>
To:	"Darrick J. Wong" <djwong@...ibm.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 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
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> 

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().

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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