From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dan Carpenter Date: Tue, 19 Feb 2019 14:40:30 +0000 Subject: Re: [PATCH][next][V2] block: don't dereference a potential null bio pointer until is has been null c Message-Id: <20190219144030.GL17104@kadam> List-Id: References: <20190219143702.11926-1-colin.king@canonical.com> In-Reply-To: <20190219143702.11926-1-colin.king@canonical.com> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Colin King Cc: Jens Axboe , linux-block@vger.kernel.org, kernel-janitors@vger.kernel.org, linux-kernel@vger.kernel.org On Tue, Feb 19, 2019 at 02:37:02PM +0000, Colin King wrote: > From: Colin Ian King > > The bio pointer is being null checked hence it can be potentially null, > however earlier it is being derefefenced on the assignment of front_seg_size. > Avoid the dereference issue by only assigning front_seg_size after bios has > been null sanity checked. > > Fixes: dcebd755926b ("block: use bio_for_each_bvec() to compute multi-page bvec count") > Signed-off-by: Colin Ian King > --- > > V2: remove front_seg_size assignment when it is declared > > --- > block/blk-merge.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/block/blk-merge.c b/block/blk-merge.c > index bed065904677..096947413ea9 100644 > --- a/block/blk-merge.c > +++ b/block/blk-merge.c > @@ -363,7 +363,7 @@ static unsigned int __blk_recalc_rq_segments(struct request_queue *q, > struct bio_vec bv, bvprv = { NULL }; > int prev = 0; > unsigned int seg_size, nr_phys_segs; > - unsigned front_seg_size = bio->bi_seg_front_size; > + unsigned front_seg_size; Smatch says bio is non-NULL but I didn't verify by hand. regards, dan carpenter