[5/5] libext2fs: avoid 32-bit overflow in ext2fs_initialize with a 512M cluster size

If the user attemps to create a 512MB cluster, we need to adjust the
defaults to avoid a 32-bit overflow of s_blocks_per_group.  Also check
to make sure that the caller of ext2fs_initialize() has not given a
value of s_clusters_per_group that would result in an overflow of
s_blocks_per_group.

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
---
 lib/ext2fs/initialize.c | 15 ++++++++++++---
 1 file changed, 12 insertions(+), 3 deletions(-)

On Mon, Jan 14, 2013 at 07:37:12PM -0500, Theodore Ts'o wrote:
> If the user attemps to create a 512MB cluster, we need to adjust the
> defaults to avoid a 32-bit overflow of s_blocks_per_group.  Also check
> to make sure that the caller of ext2fs_initialize() has not given a
> value of s_clusters_per_group that would result in an overflow of
> s_blocks_per_group.
> 
> Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

The patch itself looks good to me.  Feel free to add:
Reviewed-by: Zheng Liu <wenqing.lz@taobao.com>

FWIW, I wonder why we need to add such complex logical to handle a
corner case.  I guess no one wants to use a 512MB cluster.  So changing
max cluster size from 512MB to 256MB is very simple and straightfoward.

Regards,
                                                - Zheng

> ---
>  lib/ext2fs/initialize.c | 15 ++++++++++++---
>  1 file changed, 12 insertions(+), 3 deletions(-)
> 
> diff --git a/lib/ext2fs/initialize.c b/lib/ext2fs/initialize.c
> index b0c15d2..5afdc27 100644
> --- a/lib/ext2fs/initialize.c
> +++ b/lib/ext2fs/initialize.c
> @@ -207,6 +207,8 @@ errcode_t ext2fs_initialize(const char *name, int flags,
>  		super->s_log_block_size;
>  
>  	if (bigalloc_flag) {
> +		unsigned long long bpg;
> +
>  		if (param->s_blocks_per_group &&
>  		    param->s_clusters_per_group &&
>  		    ((param->s_clusters_per_group * EXT2FS_CLUSTER_RATIO(fs)) !=
> @@ -220,12 +222,19 @@ errcode_t ext2fs_initialize(const char *name, int flags,
>  			super->s_clusters_per_group = 
>  				param->s_blocks_per_group /
>  				EXT2FS_CLUSTER_RATIO(fs);
> -		else
> +		else if (super->s_log_cluster_size + 15 < 32)
>  			super->s_clusters_per_group = fs->blocksize * 8;
> +		else
> +			super->s_clusters_per_group = (fs->blocksize - 1) * 8;
>  		if (super->s_clusters_per_group > EXT2_MAX_CLUSTERS_PER_GROUP(super))
>  			super->s_clusters_per_group = EXT2_MAX_CLUSTERS_PER_GROUP(super);
> -		super->s_blocks_per_group = EXT2FS_C2B(fs,
> -				       super->s_clusters_per_group);
> +		bpg = EXT2FS_C2B(fs,
> +			(unsigned long long) super->s_clusters_per_group);
> +		if (bpg >= (((unsigned long long) 1) << 32)) {
> +			retval = EXT2_ET_INVALID_ARGUMENT;
> +			goto cleanup;
> +		}
> +		super->s_blocks_per_group = bpg;
>  	} else {
>  		set_field(s_blocks_per_group, fs->blocksize * 8);
>  		if (super->s_blocks_per_group > EXT2_MAX_BLOCKS_PER_GROUP(super))
> -- 
> 1.7.12.rc0.22.gcdd159b
> 
--
To unsubscribe from this list: send the line "unsubscribe linux-ext4" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html

On Tue, Jan 15, 2013 at 11:33:31PM +0800, Zheng Liu wrote:
> On Mon, Jan 14, 2013 at 07:37:12PM -0500, Theodore Ts'o wrote:
> > If the user attemps to create a 512MB cluster, we need to adjust the
> > defaults to avoid a 32-bit overflow of s_blocks_per_group.  Also check
> > to make sure that the caller of ext2fs_initialize() has not given a
> > value of s_clusters_per_group that would result in an overflow of
> > s_blocks_per_group.
> > 
> > Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
> 
> The patch itself looks good to me.  Feel free to add:
> Reviewed-by: Zheng Liu <wenqing.lz@taobao.com>

Sorry, forgot to say that '-C' option in manpage will need to be modified
from 256MB to 512MB if this patch is applied.

Thanks,
                                                - Zheng
--
To unsubscribe from this list: send the line "unsubscribe linux-ext4" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html

On Tue, Jan 15, 2013 at 11:33:31PM +0800, Zheng Liu wrote:
> 
> FWIW, I wonder why we need to add such complex logical to handle a
> corner case.  I guess no one wants to use a 512MB cluster.  So changing
> max cluster size from 512MB to 256MB is very simple and straightfoward.

I agree that it seems very unlikely that there would be much interest
in using a 512MB cluster.  However, we would still need to do the
check in the case of a 16k block size (on an PowerPC or Itanium
system) at a 256MB or 128MB cluster.  So part of this check would be
needed anyway.

						- Ted
--
To unsubscribe from this list: send the line "unsubscribe linux-ext4" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html

On Tue, Jan 15, 2013 at 02:10:30PM -0500, Theodore Ts'o wrote:
> On Tue, Jan 15, 2013 at 11:33:31PM +0800, Zheng Liu wrote:
> > 
> > FWIW, I wonder why we need to add such complex logical to handle a
> > corner case.  I guess no one wants to use a 512MB cluster.  So changing
> > max cluster size from 512MB to 256MB is very simple and straightfoward.
> 
> I agree that it seems very unlikely that there would be much interest
> in using a 512MB cluster.  However, we would still need to do the
> check in the case of a 16k block size (on an PowerPC or Itanium
> system) at a 256MB or 128MB cluster.  So part of this check would be
> needed anyway.

Yeah, I see.  Thanks for the explanation.

Regards,
                                                - Zheng
--
To unsubscribe from this list: send the line "unsubscribe linux-ext4" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html