Re: [PATCH v7 1/8] block: ensure bios are not split in middle of crypto data unit

[Eric Biggers <ebiggers@kernel.org>]

On Tue, Nov 17, 2020 at 02:07:01PM +0000, Satya Tangirala wrote:
> @@ -275,11 +331,24 @@ static struct bio *blk_bio_segment_split(struct request_queue *q,
>  		bvprvp = &bvprv;
>  	}
>  
> +	/*
> +	 * The input bio's number of sectors is assumed to be aligned to
> +	 * bio_sectors_alignment. If that's the case, then this function should
> +	 * ensure that aligned_segs == nsegs and aligned_sectors == sectors if
> +	 * the bio is not going to be split.
> +	 */
> +	WARN_ON(aligned_segs != nsegs || aligned_sectors != sectors);
>  	*segs = nsegs;
>  	return NULL;
>  split:
> -	*segs = nsegs;
> -	return bio_split(bio, sectors, GFP_NOIO, bs);
> +	*segs = aligned_segs;
> +	if (WARN_ON(aligned_sectors == 0))
> +		goto err;
> +	return bio_split(bio, aligned_sectors, GFP_NOIO, bs);
> +err:
> +	bio->bi_status = BLK_STS_IOERR;
> +	bio_endio(bio);
> +	return bio;
>  }
[...]
> diff --git a/block/blk-mq.c b/block/blk-mq.c
> index 55bcee5dc032..de5c97ab8e5a 100644
> --- a/block/blk-mq.c
> +++ b/block/blk-mq.c
> @@ -2161,6 +2161,9 @@ blk_qc_t blk_mq_submit_bio(struct bio *bio)
>  	blk_queue_bounce(q, &bio);
>  	__blk_queue_split(&bio, &nr_segs);
>  
> +	if (bio->bi_status != BLK_STS_OK)
> +		goto queue_exit;
> +

Note that as soon as bio_endio() is called, the bio may be freed.

So accessing the bio after that is not correct.

- Eric