ACK: [SRU][M][PATCH 1/1] ext4: fix double-free of blocks due to wrong extents moved_len

[Roxana Nicolescu]

On 19/04/2024 23:28, Bethany Jamison wrote:
> From: Baokun Li <libaokun1 at huawei.com>
>
> commit 55583e899a5357308274601364741a83e78d6ac4 upstream.
>
> 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 at gmail.com>
> Reported-by: xingwei lee <xrivendell7 at gmail.com>
> Closes: https://lore.kernel.org/r/CAO4mrferzqBUnCag8R3m2zf897ts9UEuhjFQGPtODT92rYyR2Q@mail.gmail.com
> Fixes: fcf6b1b729bc ("ext4: refactor ext4_move_extents code base")
> CC:  <stable at vger.kernel.org> # 3.18
> Signed-off-by: Baokun Li <libaokun1 at huawei.com>
> Reviewed-by: Jan Kara <jack at suse.cz>
> Link: https://lore.kernel.org/r/20240104142040.2835097-2-libaokun1@huawei.com
> Signed-off-by: Theodore Ts'o <tytso at mit.edu>
> Signed-off-by: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
> (cherry picked from commit 2883940b19c38d5884c8626483811acf4d7e148f linux.6.6.y)
> CVE-2024-26704
> Signed-off-by: Bethany Jamison <bethany.jamison at canonical.com>
> ---
>   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 251584a23d05f..00ba8ca8fd604 100644
> --- a/fs/ext4/move_extent.c
> +++ b/fs/ext4/move_extent.c
> @@ -622,6 +622,7 @@ 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;
> @@ -676,7 +677,7 @@ 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);
> @@ -686,9 +687,6 @@ 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) {
Acked-by: Roxana Nicolescu <roxana.nicolescu at canonical.com>