[dm-devel] [PATCH] accessing invalid memory in "dm zoned: properly handle backing device failure"

[Damien Le Moal]

On 2019/08/26 15:41, Mikulas Patocka wrote:
> The patch 75d66ffb48efb30f2dd42f041ba8b39c5b2bd115 ("dm zoned: properly 
> handle backing device failure") triggers a coverity warning:
> 
> *** CID 1452808:  Memory - illegal accesses  (USE_AFTER_FREE)
> /drivers/md/dm-zoned-target.c: 137 in dmz_submit_bio()
> 131             clone->bi_private = bioctx;
> 132
> 133             bio_advance(bio, clone->bi_iter.bi_size);
> 134
> 135             refcount_inc(&bioctx->ref);
> 136             generic_make_request(clone);
>>>>     CID 1452808:  Memory - illegal accesses  (USE_AFTER_FREE)
>>>>     Dereferencing freed pointer "clone".
> 137             if (clone->bi_status == BLK_STS_IOERR)
> 138                     return -EIO;
> 139
> 140             if (bio_op(bio) == REQ_OP_WRITE && dmz_is_seq(zone))
> 141                     zone->wp_block += nr_blocks;
> 142
> 
> The "clone" bio may be processed and freed before the check 
> "clone->bi_status == BLK_STS_IOERR" - so this check can access invalid 
> memory.
> 
> Signed-off-by: Mikulas Patocka <mpatocka at redhat.com>
> Cc: stable at vger.kernel.org
> 
> ---
>  drivers/md/dm-zoned-target.c |    2 --
>  1 file changed, 2 deletions(-)
> 
> Index: linux-2.6/drivers/md/dm-zoned-target.c
> ===================================================================
> --- linux-2.6.orig/drivers/md/dm-zoned-target.c	2019-08-26 08:30:30.000000000 +0200
> +++ linux-2.6/drivers/md/dm-zoned-target.c	2019-08-26 08:36:23.000000000 +0200
> @@ -134,8 +134,6 @@ static int dmz_submit_bio(struct dmz_tar
>  
>  	refcount_inc(&bioctx->ref);
>  	generic_make_request(clone);
> -	if (clone->bi_status == BLK_STS_IOERR)
> -		return -EIO;
>  
>  	if (bio_op(bio) == REQ_OP_WRITE && dmz_is_seq(zone))
>  		zone->wp_block += nr_blocks;
> 

Argh... Indeed. Thanks Mikulas.

Reviewed-by: Damien Le Moal <damien.lemoal at wdc.com>

-- 
Damien Le Moal
Western Digital Research