Re: [PATCH] block: fix NULL pointer dereferenced within __blk_rq_map_sg

[Ming Lei <ming.lei@redhat.com>]

On Fri, Feb 14, 2025 at 03:10:10PM +0100, Christoph Hellwig wrote:
> On Fri, Feb 14, 2025 at 04:46:38PM +0800, Ming Lei wrote:
> > Discard request may use special payload only and doesn't have bio
> > attached, so the request iterator has to be initialized from valid
> > req->bio, otherwise NULL pointer dereferenced is triggered.
> 
> So while the code changes here look good to me, the commit message is
> wrong.  discard requests always have at least one bio attached, so we're
> not going to hit this condition.  Discard requests also aren't even
> handled by the function in Cheyenne's report.  I'm pretty sure this is
> a flush request, as these are the only non-passthrough requests without
> a bio.
> 
> > +	/* discard request may not have bio attached */
> > +	if (iter.bio)
> > +		iter.iter = iter.bio->bi_iter;
> 
> Same for the comment.
 
You are right, it should be the flush internal request, even though
mapping discard request may not need bio, I will fix the commit log and
comment.


Thanks,
Ming