[dm-devel] [PATCH] dm: dm-zone: Fix NULL pointer dereference in dm_zone_map_bio()

[Ming Lei]

On Mon, Apr 11, 2022 at 06:38:38PM +0900, Damien Le Moal wrote:
> Commit 0fbb4d93b38b ("dm: add dm_submit_bio_remap interface") changed
> the alloc_io() function to delay the initialization of struct dm_io
> orig_bio field, leaving this field as NULL until the first call to
> __split_and_process_bio() is executed for the user submitted BIO. This
> change causes a NULL pointer dereference in dm_zone_map_bio() when the
> original user BIO is inspected to detect the need for zone append
> command emulation.
> 
> Avoid this problem by adding a struct clone_info *ci argument to the
> __map_bio() function and a struct bio *orig_bio argument to
> dm_zone_map_bio(). Doing so, the call to dm_zone_map_bio() can be passed
> directly a pointer to the original user BIO using the bio field of
> struct clone_info.
> 
> Fixes: 0fbb4d93b38b ("dm: add dm_submit_bio_remap interface")
> Signed-off-by: Damien Le Moal <damien.lemoal at opensource.wdc.com>
> ---
>  drivers/md/dm-zone.c |  3 +--
>  drivers/md/dm.c      | 10 +++++-----
>  drivers/md/dm.h      |  5 +++--
>  3 files changed, 9 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/md/dm-zone.c b/drivers/md/dm-zone.c
> index c1ca9be4b79e..772161f0b029 100644
> --- a/drivers/md/dm-zone.c
> +++ b/drivers/md/dm-zone.c
> @@ -513,13 +513,12 @@ static bool dm_need_zone_wp_tracking(struct bio *orig_bio)
>  /*
>   * Special IO mapping for targets needing zone append emulation.
>   */
> -int dm_zone_map_bio(struct dm_target_io *tio)
> +int dm_zone_map_bio(struct dm_target_io *tio, struct bio *orig_bio)
>  {
>  	struct dm_io *io = tio->io;
>  	struct dm_target *ti = tio->ti;
>  	struct mapped_device *md = io->md;
>  	struct request_queue *q = md->queue;
> -	struct bio *orig_bio = io->orig_bio;
>  	struct bio *clone = &tio->clone;
>  	unsigned int zno;
>  	blk_status_t sts;
> diff --git a/drivers/md/dm.c b/drivers/md/dm.c
> index 3c5fad7c4ee6..1d8f24f04c7d 100644
> --- a/drivers/md/dm.c
> +++ b/drivers/md/dm.c
> @@ -1258,7 +1258,7 @@ static noinline void __set_swap_bios_limit(struct mapped_device *md, int latch)
>  	mutex_unlock(&md->swap_bios_lock);
>  }
>  
> -static void __map_bio(struct bio *clone)
> +static void __map_bio(struct clone_info *ci, struct bio *clone)
>  {
>  	struct dm_target_io *tio = clone_to_tio(clone);
>  	int r;
> @@ -1287,7 +1287,7 @@ static void __map_bio(struct bio *clone)
>  	 * map operation.
>  	 */
>  	if (dm_emulate_zone_append(io->md))
> -		r = dm_zone_map_bio(tio);
> +		r = dm_zone_map_bio(tio, ci->bio);

It depends if bio_split() in dm_split_and_process_bio() can be triggered
for dm-zone. If it can be triggered, here the actual original bio should
be the one returned from bio_split().

Thanks,
Ming