Re: [PATCH] ext4: Avoid underflow of in ext4_trim_fs()

[Carlos Maiolino <cmaiolino@redhat.com>]

On Tue, Oct 09, 2012 at 02:12:42PM +0200, Lukas Czerner wrote:
> Currently if len argument in ext4_trim_fs() is smaller than one block,
> the 'end' variable underflow. Avoid that by exiting right away if len
> is smaller than one file system block.
> 
> Signed-off-by: Lukas Czerner <lczerner@redhat.com>
> ---
>  fs/ext4/mballoc.c |    7 ++++++-
>  1 files changed, 6 insertions(+), 1 deletions(-)
> 
> diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
> index f8b27bf..06c8526 100644
> --- a/fs/ext4/mballoc.c
> +++ b/fs/ext4/mballoc.c
> @@ -4989,13 +4989,18 @@ int ext4_trim_fs(struct super_block *sb, struct fstrim_range *range)
>  	int ret = 0;
>  
>  	start = range->start >> sb->s_blocksize_bits;
> -	end = start + (range->len >> sb->s_blocksize_bits) - 1;
>  	minlen = EXT4_NUM_B2C(EXT4_SB(sb),
>  			      range->minlen >> sb->s_blocksize_bits);
>  
>  	if (unlikely(minlen > EXT4_CLUSTERS_PER_GROUP(sb)) ||
>  	    unlikely(start >= max_blks))
>  		return -EINVAL;
> +
> +	end = range->len >> sb->s_blocksize_bits;
> +	if (0 == end)
> +		goto out;
> +	end += start - 1;
> +
>  	if (end >= max_blks)
>  		end = max_blks - 1;
>  	if (end <= first_data_blk)
> -- 
> 1.7.7.6
> 
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Looks good,

Reviewed-by: Carlos Maiolino <cmaiolino@redhat.com>
-- 
--Carlos