Re: [PATCH v2 1/8] ext4: fix double-free of blocks due to wrong extents moved_len

[Jan Kara]

On Thu 21-12-23 23:05:51, Baokun Li wrote:
> In ext4_move_extents(), moved_len is only updated when all moves are
> successfully executed, and only discards orig_inode and donor_inode
> preallocations when moved_len is not zero. When the loop fails to exit
> after successfully moving some extents, moved_len is not updated and
> remains at 0, so it does not discard the preallocations.
> 
> If the moved extents overlap with the preallocated extents, the
> overlapped extents are freed twice in ext4_mb_release_inode_pa() and
> ext4_process_freed_data() (as described in commit 94d7c16cbbbd ("ext4:
> Fix double-free of blocks with EXT4_IOC_MOVE_EXT")), and bb_free is
> incremented twice. Hence when trim is executed, a zero-division bug is
> triggered in mb_update_avg_fragment_size() because bb_free is not zero
> and bb_fragments is zero.
> 
> Therefore, update move_len after each extent move to avoid the issue.
> 
> Reported-by: Wei Chen <harperchen1110@xxxxxxxxx>
> Reported-by: xingwei lee <xrivendell7@xxxxxxxxx>
> Closes: https://lore.kernel.org/r/CAO4mrferzqBUnCag8R3m2zf897ts9UEuhjFQGPtODT92rYyR2Q@xxxxxxxxxxxxxx
> Fixes: fcf6b1b729bc ("ext4: refactor ext4_move_extents code base")
> CC: stable@xxxxxxxxxxxxxxx # 3.18
> Signed-off-by: Baokun Li <libaokun1@xxxxxxxxxx>

Looks good! Feel free to add:

Reviewed-by: Jan Kara <jack@xxxxxxx>

								Honza

> ---
>  fs/ext4/move_extent.c | 6 ++----
>  1 file changed, 2 insertions(+), 4 deletions(-)
> 
> diff --git a/fs/ext4/move_extent.c b/fs/ext4/move_extent.c
> index 3aa57376d9c2..391efa6d4c56 100644
> --- a/fs/ext4/move_extent.c
> +++ b/fs/ext4/move_extent.c
> @@ -618,6 +618,7 @@ ext4_move_extents(struct file *o_filp, struct file *d_filp, __u64 orig_blk,
>  		goto out;
>  	o_end = o_start + len;
>  
> +	*moved_len = 0;
>  	while (o_start < o_end) {
>  		struct ext4_extent *ex;
>  		ext4_lblk_t cur_blk, next_blk;
> @@ -672,7 +673,7 @@ ext4_move_extents(struct file *o_filp, struct file *d_filp, __u64 orig_blk,
>  		 */
>  		ext4_double_up_write_data_sem(orig_inode, donor_inode);
>  		/* Swap original branches with new branches */
> -		move_extent_per_page(o_filp, donor_inode,
> +		*moved_len += move_extent_per_page(o_filp, donor_inode,
>  				     orig_page_index, donor_page_index,
>  				     offset_in_page, cur_len,
>  				     unwritten, &ret);
> @@ -682,9 +683,6 @@ ext4_move_extents(struct file *o_filp, struct file *d_filp, __u64 orig_blk,
>  		o_start += cur_len;
>  		d_start += cur_len;
>  	}
> -	*moved_len = o_start - orig_blk;
> -	if (*moved_len > len)
> -		*moved_len = len;
>  
>  out:
>  	if (*moved_len) {
> -- 
> 2.31.1
> 
-- 
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR