[PATCH] Avoid disk sector_t overflow for >2TB ext3 filesystem

On Fri, 2006-05-19 at 00:56 -0600, Andreas Dilger wrote:
> On May 18, 2006  17:31 -0700, Mingming Cao wrote:
> > Hmm, do we have the sector overflow issue with upstream right now?? As
> > ext3 filesystem blocks account in upstream right now is unsigned long
> > type, I could be wrong but I don't think we have the sector overflow
> > issue until we have >32 bit block number support on disk?
> 
> Yes, I believe we currently have an overflow issue in the vanilla kernel
> right now.  I had been worried about this for some time already (enough
> that CFS has not supported > 2TB ext3 filesystems as a result, because
> I didn't know where the corruption was coming from) but I didn't have
> enough information to work on, only some rare but serious reports of
> ext3 corruption on large filesystems, sometimes correlated to 32-bit
> systems.
> 
> What confused me is that RHEL4 had no problem with filesystems > 2TB,
> but this is because their kernels always include CONFIG_LBD.
> 
> 
> The problem is that if sector_t is a u32 (i.e. CONFIG_LBD not defined in
> the kernel) and we are using a filesystem larger than 2TB the calculation
> of the disk sector will overflow.  This is because the a device offset
> of >= 2TB is >= 2^40 bytes is >= 2^29 4kB blocks is >= 2^32 512-byte sectors
> and we overflow the sector offset and overwrite the beginning of the disk.
> 
> So, the above check could be initially added for only the 32-bit size:
> 
> 	if (le32_to_cpu(es->s_blocks_count) >
> 	    (sector_t)(~0ULL) >> (sb->s_blocksize_bits - 9)) {
> 		printk(KERN_ERR "EXT3-fs: filesystem on %s too large to mount
> 		       safely\n", sb->s_id);
> 		if (sizeof(sector_t) < 8)
> 			printk(KERN_WARNING
> 			       "EXT3-fs: CONFIG_LBD not enabled\n");
> 		goto failed_mount;
> 	}

If ext3 filesystem is larger than 2TB, and sector_t is a u32 (i.e.
CONFIG_LBD not defined in the kernel), the calculation of the disk
sector will overflow. Add check at ext3_fill_super() and
ext3_group_extend() to prevent mount/remount/resize >2TB ext3 filesystem
if sector_t size is 4 bytes.

Verified this patch on a 32 bit platform without CONFIG_LBD defined
(sector_t is 32 bits long), mount refuse to mount a 10TB ext3. Patch
against 2.6.17-rc4.

Signed-Off-By: Mingming Cao<[email protected]>


---

 linux-2.6.16-ming/fs/ext3/resize.c |    9 +++++++++
 linux-2.6.16-ming/fs/ext3/super.c  |   10 ++++++++++
 2 files changed, 19 insertions(+)

diff -puN fs/ext3/super.c~ext3_check_sector_t_overflow fs/ext3/super.c
--- linux-2.6.16/fs/ext3/super.c~ext3_check_sector_t_overflow	2006-05-19 17:19:43.000000000 -0700
+++ linux-2.6.16-ming/fs/ext3/super.c	2006-05-22 10:54:27.000000000 -0700
@@ -1579,6 +1579,16 @@ static int ext3_fill_super (struct super
 		goto failed_mount;
 	}
 
+	if (le32_to_cpu(es->s_blocks_count) >
+		(sector_t)(~0ULL) >> (sb->s_blocksize_bits - 9)) {
+		printk(KERN_ERR "EXT3-fs: filesystem on %s"
+			" too large to mount safely\n", sb->s_id);
+		if (sizeof(sector_t) < 8)
+			printk(KERN_WARNING
+				"EXT3-fs: CONFIG_LBD not enabled\n");
+		goto failed_mount;
+	}
+
 	percpu_counter_init(&sbi->s_freeblocks_counter);
 	percpu_counter_init(&sbi->s_freeinodes_counter);
 	percpu_counter_init(&sbi->s_dirs_counter);
diff -puN fs/ext3/resize.c~ext3_check_sector_t_overflow fs/ext3/resize.c
--- linux-2.6.16/fs/ext3/resize.c~ext3_check_sector_t_overflow	2006-05-19 17:19:43.000000000 -0700
+++ linux-2.6.16-ming/fs/ext3/resize.c	2006-05-22 10:54:27.000000000 -0700
@@ -926,6 +926,15 @@ int ext3_group_extend(struct super_block
 	if (n_blocks_count == 0 || n_blocks_count == o_blocks_count)
 		return 0;
 
+	if (n_blocks_count > (sector_t)(~0ULL) >> (sb->s_blocksize_bits - 9)) {
+		printk(KERN_ERR "EXT3-fs: filesystem on %s"
+			" too large to mount safely\n", sb->s_id);
+		if (sizeof(sector_t) < 8)
+			ext3_warning(sb, __FUNCTION__,
+			"CONFIG_LBD not enabled\n");
+		return -EINVAL;
+	}
+
 	if (n_blocks_count < o_blocks_count) {
 		ext3_warning(sb, __FUNCTION__,
 			     "can't shrink FS - resize aborted");

_





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