Message-ID: <ca552165dc70f8268b887bc35d395039ed093861.camel@kernel.org>
Subject: Re: [PATCH 2/2] sunrpc: add bounds checking to svc_rqst_replace_page
From:   Jeff Layton <jlayton@kernel.org>
To:     Chuck Lever III <chuck.lever@oracle.com>
Cc:     Linux NFS Mailing List <linux-nfs@vger.kernel.org>,
        "dcritch@redhat.com" <dcritch@redhat.com>,
        "d.lesca@solinos.it" <d.lesca@solinos.it>
Date:   Fri, 17 Mar 2023 09:52:47 -0400
In-Reply-To: <7DAC68F4-8CE7-4578-BBF1-626285B44B6E@oracle.com>
References: <20230317105608.19393-1-jlayton@kernel.org>
         <20230317105608.19393-2-jlayton@kernel.org>
         <7DAC68F4-8CE7-4578-BBF1-626285B44B6E@oracle.com>
Content-Type: text/plain; charset="ISO-8859-15"
Content-Transfer-Encoding: quoted-printable
User-Agent: Evolution 3.46.4 (3.46.4-1.fc37) 
MIME-Version: 1.0
Precedence: bulk

On Fri, 2023-03-17 at 13:44 +0000, Chuck Lever III wrote:
>=20
> > On Mar 17, 2023, at 6:56 AM, Jeff Layton <jlayton@kernel.org> wrote:
> >=20
> > There's no good way to handle this gracefully, but if rq_next_page ends
> > up pointing outside the array, we can at least crash the box before it
> > scribbles over too much else.
> >=20
> > Signed-off-by: Jeff Layton <jlayton@kernel.org>
> > ---
> > net/sunrpc/svc.c | 10 ++++++++++
> > 1 file changed, 10 insertions(+)
> >=20
> > diff --git a/net/sunrpc/svc.c b/net/sunrpc/svc.c
> > index fea7ce8fba14..864e62945647 100644
> > --- a/net/sunrpc/svc.c
> > +++ b/net/sunrpc/svc.c
> > @@ -845,6 +845,16 @@ EXPORT_SYMBOL_GPL(svc_set_num_threads);
> >  */
> > void svc_rqst_replace_page(struct svc_rqst *rqstp, struct page *page)
> > {
> > +	struct page **begin, **end;
> > +
> > +	/*
> > +	 * Bounds check: make sure rq_next_page points into the rq_respages
> > +	 * part of the array.
> > +	 */
> > +	begin =3D rqstp->rq_pages;
> > +	end =3D &rqstp->rq_pages[RPCSVC_MAXPAGES];
> > +	BUG_ON(rqstp->rq_next_page < begin || rqstp->rq_next_page > end);
>=20
> Linus has stated clearly that he does not want BUG_ON assertions
> if the system is not actually in danger... and this is clearly
> the result of a software bug, so a crash will occur anyway.
>=20

It'll crash, but only after we scribble over some memory.

Actually, it looks like the splice actor can return an error. We could
return -EIO here or something without doing anything if we hit this case
and then let that bubble back up to the read?

> Can you make this a pr_warn_once() ?
>=20
>=20
> > +
> > 	if (*rqstp->rq_next_page) {
> > 		if (!pagevec_space(&rqstp->rq_pvec))
> > 			__pagevec_release(&rqstp->rq_pvec);
> > --=20
> > 2.39.2
> >=20
>=20
> --
> Chuck Lever
>=20
>=20

--=20
Jeff Layton <jlayton@kernel.org>