Re: [PATCH 1/4 v2] ext4: fix start and len arguments handling in ext4_trim_fs()

[Jan Kara <jack@suse.cz>]

On Fri 02-03-12 13:11:55, Lukas Czerner wrote:
> The overflow can happen when we are calling get_group_no_and_offset()
> which stores the group number in the ext4_grpblk_t type which is
> actually int. However when the blocknr is big enough the group number
> might be bigger than ext4_grpblk_t resulting in overflow. This will
> most likely happen with FITRIM default argument len = ULLONG_MAX.
> 
> Fix this by using "end" variable instead of "start+len" as it is easier
> to get right and specifically check that the end is not beyond the end
> of the file system, so we are sure that the result of
> get_group_no_and_offset() will not overflow. Otherwise truncate it to
> the size of the file system.
  Looks good. You can add:
Reviewed-by: Jan Kara <jack@suse.cz>

								Honza

> 
> Signed-off-by: Lukas Czerner <lczerner@redhat.com>
> ---
> v2: Squash the 'don't forget to discard last block in a group' into this one
>     since this is the commit which reveals the bug.
> 
>  fs/ext4/mballoc.c |   57 +++++++++++++++++++++++++++-------------------------
>  1 files changed, 30 insertions(+), 27 deletions(-)
> 
> diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
> index cb990b2..16a3aeb 100644
> --- a/fs/ext4/mballoc.c
> +++ b/fs/ext4/mballoc.c
> @@ -4971,11 +4971,11 @@ ext4_trim_all_free(struct super_block *sb, ext4_group_t group,
>  	start = (e4b.bd_info->bb_first_free > start) ?
>  		e4b.bd_info->bb_first_free : start;
>  
> -	while (start < max) {
> -		start = mb_find_next_zero_bit(bitmap, max, start);
> -		if (start >= max)
> +	while (start <= max) {
> +		start = mb_find_next_zero_bit(bitmap, max + 1, start);
> +		if (start > max)
>  			break;
> -		next = mb_find_next_bit(bitmap, max, start);
> +		next = mb_find_next_bit(bitmap, max + 1, start);
>  
>  		if ((next - start) >= minblocks) {
>  			ext4_trim_extent(sb, start,
> @@ -5027,37 +5027,36 @@ out:
>  int ext4_trim_fs(struct super_block *sb, struct fstrim_range *range)
>  {
>  	struct ext4_group_info *grp;
> -	ext4_group_t first_group, last_group;
> -	ext4_group_t group, ngroups = ext4_get_groups_count(sb);
> +	ext4_group_t group, first_group, last_group;
>  	ext4_grpblk_t cnt = 0, first_cluster, last_cluster;
> -	uint64_t start, len, minlen, trimmed = 0;
> +	uint64_t start, end, minlen, trimmed = 0;
>  	ext4_fsblk_t first_data_blk =
>  			le32_to_cpu(EXT4_SB(sb)->s_es->s_first_data_block);
> +	ext4_fsblk_t max_blks = ext4_blocks_count(EXT4_SB(sb)->s_es);
>  	int ret = 0;
>  
>  	start = range->start >> sb->s_blocksize_bits;
> -	len = range->len >> sb->s_blocksize_bits;
> +	end = start + (range->len >> sb->s_blocksize_bits) - 1;
>  	minlen = range->minlen >> sb->s_blocksize_bits;
>  
> -	if (unlikely(minlen > EXT4_CLUSTERS_PER_GROUP(sb)))
> +	if (unlikely(minlen > EXT4_CLUSTERS_PER_GROUP(sb)) ||
> +	    unlikely(start >= max_blks))
>  		return -EINVAL;
> -	if (start + len <= first_data_blk)
> +	if (end >= max_blks)
> +		end = max_blks - 1;
> +	if (end <= first_data_blk)
>  		goto out;
> -	if (start < first_data_blk) {
> -		len -= first_data_blk - start;
> +	if (start < first_data_blk)
>  		start = first_data_blk;
> -	}
>  
> -	/* Determine first and last group to examine based on start and len */
> +	/* Determine first and last group to examine based on start and end */
>  	ext4_get_group_no_and_offset(sb, (ext4_fsblk_t) start,
>  				     &first_group, &first_cluster);
> -	ext4_get_group_no_and_offset(sb, (ext4_fsblk_t) (start + len),
> +	ext4_get_group_no_and_offset(sb, (ext4_fsblk_t) end,
>  				     &last_group, &last_cluster);
> -	last_group = (last_group > ngroups - 1) ? ngroups - 1 : last_group;
> -	last_cluster = EXT4_CLUSTERS_PER_GROUP(sb);
>  
> -	if (first_group > last_group)
> -		return -EINVAL;
> +	/* end now represents the last cluster to discard in this group */
> +	end = EXT4_CLUSTERS_PER_GROUP(sb) - 1;
>  
>  	for (group = first_group; group <= last_group; group++) {
>  		grp = ext4_get_group_info(sb, group);
> @@ -5069,24 +5068,28 @@ int ext4_trim_fs(struct super_block *sb, struct fstrim_range *range)
>  		}
>  
>  		/*
> -		 * For all the groups except the last one, last block will
> -		 * always be EXT4_BLOCKS_PER_GROUP(sb), so we only need to
> -		 * change it for the last group in which case start +
> -		 * len < EXT4_BLOCKS_PER_GROUP(sb).
> +		 * For all the groups except the last one, last cluster will
> +		 * always be EXT4_CLUSTERS_PER_GROUP(sb)-1, so we only need to
> +		 * change it for the last group, note that last_cluster is
> +		 * already computed earlier by ext4_get_group_no_and_offset()
>  		 */
> -		if (first_cluster + len < EXT4_CLUSTERS_PER_GROUP(sb))
> -			last_cluster = first_cluster + len;
> -		len -= last_cluster - first_cluster;
> +		if (group == last_group)
> +			end = last_cluster;
>  
>  		if (grp->bb_free >= minlen) {
>  			cnt = ext4_trim_all_free(sb, group, first_cluster,
> -						last_cluster, minlen);
> +						end, minlen);
>  			if (cnt < 0) {
>  				ret = cnt;
>  				break;
>  			}
>  		}
>  		trimmed += cnt;
> +
> +		/*
> +		 * For every group except the first one, we are sure
> +		 * that the first cluster to discard will be cluster #0.
> +		 */
>  		first_cluster = 0;
>  	}
>  	range->len = trimmed * sb->s_blocksize;
> -- 
> 1.7.4.4
> 
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-- 
Jan Kara <jack@suse.cz>
SUSE Labs, CR