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Date:   Wed, 25 Nov 2020 14:15:03 -0800
From:   Eric Biggers <ebiggers@kernel.org>
To:     Satya Tangirala <satyat@google.com>
Cc:     "Theodore Y . Ts'o" <tytso@mit.edu>,
        Jaegeuk Kim <jaegeuk@kernel.org>, Chao Yu <chao@kernel.org>,
        Jens Axboe <axboe@kernel.dk>,
        "Darrick J . Wong" <darrick.wong@oracle.com>,
        linux-kernel@vger.kernel.org, linux-fscrypt@vger.kernel.org,
        linux-f2fs-devel@lists.sourceforge.net, linux-xfs@vger.kernel.org,
        linux-block@vger.kernel.org, linux-ext4@vger.kernel.org
Subject: Re: [PATCH v7 1/8] block: ensure bios are not split in middle of
 crypto data unit
Message-ID: <X77XZ/WVIuw9aCHb@sol.localdomain>
References: <20201117140708.1068688-1-satyat@google.com>
 <20201117140708.1068688-2-satyat@google.com>
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Precedence: bulk

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