[PATCH] don't divide by 0 when trying to mount ext3

[PATCH] don't divide by 0 when trying to mount ext3

[Andries Brouwer]

Not surprisingly, the ext3 code crashes in the same way
the ext2 code does when dividing by zero.

diff -uprN -X /linux/dontdiff a/fs/ext3/super.c b/fs/ext3/super.c
--- a/fs/ext3/super.c	2004-10-30 21:44:02.000000000 +0200
+++ b/fs/ext3/super.c	2004-11-08 20:55:30.000000000 +0100
@@ -1259,13 +1259,8 @@ static int ext3_fill_super (struct super
 	es = (struct ext3_super_block *) (((char *)bh->b_data) + offset);
 	sbi->s_es = es;
 	sb->s_magic = le16_to_cpu(es->s_magic);
-	if (sb->s_magic != EXT3_SUPER_MAGIC) {
-		if (!silent)
-			printk(KERN_ERR 
-			       "VFS: Can't find ext3 filesystem on dev %s.\n",
-			       sb->s_id);
-		goto failed_mount;
-	}
+	if (sb->s_magic != EXT3_SUPER_MAGIC)
+		goto cantfind_ext3;
 
 	/* Set defaults before we parse the mount options */
 	def_mount_opts = le32_to_cpu(es->s_default_mount_opts);
@@ -1397,8 +1392,13 @@ static int ext3_fill_super (struct super
 	sbi->s_blocks_per_group = le32_to_cpu(es->s_blocks_per_group);
 	sbi->s_frags_per_group = le32_to_cpu(es->s_frags_per_group);
 	sbi->s_inodes_per_group = le32_to_cpu(es->s_inodes_per_group);
+	if (EXT3_INODE_SIZE(sb) == 0)
+		goto cantfind_ext3;
 	sbi->s_inodes_per_block = blocksize / EXT3_INODE_SIZE(sb);
-	sbi->s_itb_per_group = sbi->s_inodes_per_group /sbi->s_inodes_per_block;
+	if (sbi->s_inodes_per_block == 0)
+		goto cantfind_ext3;
+	sbi->s_itb_per_group = sbi->s_inodes_per_group /
+					sbi->s_inodes_per_block;
 	sbi->s_desc_per_block = blocksize / sizeof(struct ext3_group_desc);
 	sbi->s_sbh = bh;
 	sbi->s_mount_state = le16_to_cpu(es->s_state);
@@ -1427,6 +1427,8 @@ static int ext3_fill_super (struct super
 		goto failed_mount;
 	}
 
+	if (EXT3_BLOCKS_PER_GROUP(sb) == 0)
+		goto cantfind_ext3;
 	sbi->s_groups_count = (le32_to_cpu(es->s_blocks_count) -
 			       le32_to_cpu(es->s_first_data_block) +
 			       EXT3_BLOCKS_PER_GROUP(sb) - 1) /
@@ -1579,6 +1581,12 @@ static int ext3_fill_super (struct super
 
 	return 0;
 
+cantfind_ext3:
+	if (!silent)
+		printk(KERN_ERR "VFS: Can't find ext3 filesystem on dev %s.\n",
+		       sb->s_id);
+	goto failed_mount;
+
 failed_mount3:
 	journal_destroy(sbi->s_journal);
 failed_mount2:
@@ -1588,10 +1596,8 @@ failed_mount2:
 	kfree(sbi->s_group_desc);
 failed_mount:
 #ifdef CONFIG_QUOTA
-	for (i = 0; i < MAXQUOTAS; i++) {
-		if (sbi->s_qf_names[i])
-			kfree(sbi->s_qf_names[i]);
-	}
+	for (i = 0; i < MAXQUOTAS; i++)
+		kfree(sbi->s_qf_names[i]);
 #endif
 	ext3_blkdev_remove(sbi);
 	brelse(bh);

Re: [PATCH] don't divide by 0 when trying to mount ext3

[Rogier Wolff]

On Mon, Nov 08, 2004 at 08:59:35PM +0100, Andries Brouwer wrote:
> Not surprisingly, the ext3 code crashes in the same way
> the ext2 code does when dividing by zero.


> +	if (sb->s_magic != EXT3_SUPER_MAGIC)
> +		goto cantfind_ext3;
[...]
> +	if (EXT3_INODE_SIZE(sb) == 0)
> +		goto cantfind_ext3;
[...] 
> +	if (EXT3_BLOCKS_PER_GROUP(sb) == 0)
> +		goto cantfind_ext3;

[...]
> +cantfind_ext3:
> +	if (!silent)
> +		printk(KERN_ERR "VFS: Can't find ext3 filesystem on dev %s.\n",
> +		       sb->s_id);
> +	goto failed_mount;

There are now three cases that end up with the same message and
same error from userspace viewpoint. There are many cases where 
debugging a problem is helped when it's possible to find out exactly
which test determined that the filesystem could not be mounted. 

How about: 

	[ ... ]	{
	errstr = "no magic";
	goto cantfind_ext3;
	}

-- 
** R.E.Wolff@BitWizard.nl ** http://www.BitWizard.nl/ ** +31-15-2600998 **
*-- BitWizard writes Linux device drivers for any device you may have! --*
Q: It doesn't work. A: Look buddy, doesn't work is an ambiguous statement. 
Does it sit on the couch all day? Is it unemployed? Please be specific! 
Define 'it' and what it isn't doing. --------- Adapted from lxrbot FAQ

Re: [PATCH] don't divide by 0 when trying to mount ext3

[Andries Brouwer]

On Mon, Nov 08, 2004 at 10:27:11PM +0100, Rogier Wolff wrote:

> There are now three cases that end up with the same message and
> same error from userspace viewpoint. There are many cases where 
> debugging a problem is helped when it's possible to find out exactly
> which test determined that the filesystem could not be mounted. 

Strings are expensive. Don't like to add worthless code.
We lived without this for years, so it is not a frequent occurrence.
If you have a bad ext2/ext3 system, e2fsck will find what is wrong.

Re: [PATCH] don't divide by 0 when trying to mount ext3

[Rogier Wolff]

On Mon, Nov 08, 2004 at 10:54:02PM +0100, Andries Brouwer wrote:
> On Mon, Nov 08, 2004 at 10:27:11PM +0100, Rogier Wolff wrote:
> 
> > There are now three cases that end up with the same message and
> > same error from userspace viewpoint. There are many cases where 
> > debugging a problem is helped when it's possible to find out exactly
> > which test determined that the filesystem could not be mounted. 
> 
> Strings are expensive. Don't like to add worthless code.
> We lived without this for years, so it is not a frequent occurrence.
> If you have a bad ext2/ext3 system, e2fsck will find what is wrong.

   int cpos=0;

   if (++cpos && (errorposibility1 ) ) goto error_handling;
[...]
   if (++cpos && (errorposibility2 ) ) goto error_handling;
[...]
   if (++cpos && (errorposibility3 ) ) goto error_handling;
[...]
error_handling:

     printk (".... %d ...", cpos); 

Rogier. 
-- 
** R.E.Wolff@BitWizard.nl ** http://www.BitWizard.nl/ ** +31-15-2600998 **
*-- BitWizard writes Linux device drivers for any device you may have! --*
Q: It doesn't work. A: Look buddy, doesn't work is an ambiguous statement. 
Does it sit on the couch all day? Is it unemployed? Please be specific! 
Define 'it' and what it isn't doing. --------- Adapted from lxrbot FAQ