Message-ID: <d4c2556fa6e9063c4c8981aa3ae87f70d7b9aeb8.camel@kernel.org>
Subject: Re: [PATCH v2 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>,
        Al Viro <viro@zeniv.linux.org.uk>
Date:   Fri, 17 Mar 2023 14:52:41 -0400
In-Reply-To: <D67DF2B8-75E1-4468-B264-139A21F1032F@oracle.com>
References: <20230317171309.73607-1-jlayton@kernel.org>
         <20230317171309.73607-2-jlayton@kernel.org>
         <D67DF2B8-75E1-4468-B264-139A21F1032F@oracle.com>
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On Fri, 2023-03-17 at 18:32 +0000, Chuck Lever III wrote:
>=20
> > On Mar 17, 2023, at 1:13 PM, Jeff Layton <jlayton@kernel.org> wrote:
> >=20
> > If rq_next_page ends up pointing outside the array, then we can corrupt
> > memory when we go to change its value. Ensure that it hasn't strayed
> > outside the array, and have svc_rqst_replace_page return -EIO without
> > changing anything if it has.
> >=20
> > Fix up nfsd_splice_actor (the only caller) to handle this case by eithe=
r
> > returning an error or a short splice when this happens.
> >=20
> > Signed-off-by: Jeff Layton <jlayton@kernel.org>
> > ---
> > fs/nfsd/vfs.c              | 23 +++++++++++++++++------
> > include/linux/sunrpc/svc.h |  2 +-
> > net/sunrpc/svc.c           | 14 +++++++++++++-
> > 3 files changed, 31 insertions(+), 8 deletions(-)
> >=20
> > diff --git a/fs/nfsd/vfs.c b/fs/nfsd/vfs.c
> > index 97b38b47c563..0ebd7a65a9f0 100644
> > --- a/fs/nfsd/vfs.c
> > +++ b/fs/nfsd/vfs.c
> > @@ -939,6 +939,7 @@ nfsd_splice_actor(struct pipe_inode_info *pipe, str=
uct pipe_buffer *buf,
> > 	struct page *page =3D buf->page;	// may be a compound one
> > 	unsigned offset =3D buf->offset;
> > 	struct page *last_page;
> > +	int ret =3D 0, consumed =3D 0;
> >=20
> > 	last_page =3D page + (offset + sd->len - 1) / PAGE_SIZE;
> > 	for (page +=3D offset / PAGE_SIZE; page <=3D last_page; page++) {
> > @@ -946,13 +947,23 @@ nfsd_splice_actor(struct pipe_inode_info *pipe, s=
truct pipe_buffer *buf,
> > 		 * Skip page replacement when extending the contents
> > 		 * of the current page.
> > 		 */
> > -		if (page !=3D *(rqstp->rq_next_page - 1))
> > -			svc_rqst_replace_page(rqstp, page);
> > +		if (page !=3D *(rqstp->rq_next_page - 1)) {
> > +			ret =3D svc_rqst_replace_page(rqstp, page);
> > +			if (ret)
> > +				break;
> > +		}
> > +		consumed +=3D min_t(int,
> > +				  PAGE_SIZE - offset_in_page(offset),
> > +				  sd->len - consumed);
> > +		offset =3D 0;
> > 	}
> > -	if (rqstp->rq_res.page_len =3D=3D 0)	// first call
> > -		rqstp->rq_res.page_base =3D offset % PAGE_SIZE;
> > -	rqstp->rq_res.page_len +=3D sd->len;
> > -	return sd->len;
> > +	if (consumed) {
> > +		if (rqstp->rq_res.page_len =3D=3D 0)	// first call
> > +			rqstp->rq_res.page_base =3D offset % PAGE_SIZE;
> > +		rqstp->rq_res.page_len +=3D consumed;
> > +		return consumed;
> > +	}
> > +	return ret;
> > }
> >=20
> > static int nfsd_direct_splice_actor(struct pipe_inode_info *pipe,
> > diff --git a/include/linux/sunrpc/svc.h b/include/linux/sunrpc/svc.h
> > index 877891536c2f..9ea52f143f49 100644
> > --- a/include/linux/sunrpc/svc.h
> > +++ b/include/linux/sunrpc/svc.h
> > @@ -422,7 +422,7 @@ struct svc_serv *svc_create(struct svc_program *, u=
nsigned int,
> > 			    int (*threadfn)(void *data));
> > struct svc_rqst *svc_rqst_alloc(struct svc_serv *serv,
> > 					struct svc_pool *pool, int node);
> > -void		   svc_rqst_replace_page(struct svc_rqst *rqstp,
> > +int		   svc_rqst_replace_page(struct svc_rqst *rqstp,
> > 					 struct page *page);
> > void		   svc_rqst_free(struct svc_rqst *);
> > void		   svc_exit_thread(struct svc_rqst *);
> > diff --git a/net/sunrpc/svc.c b/net/sunrpc/svc.c
> > index fea7ce8fba14..d624c02f09be 100644
> > --- a/net/sunrpc/svc.c
> > +++ b/net/sunrpc/svc.c
> > @@ -843,8 +843,19 @@ EXPORT_SYMBOL_GPL(svc_set_num_threads);
> >  * When replacing a page in rq_pages, batch the release of the
> >  * replaced pages to avoid hammering the page allocator.
> >  */
> > -void svc_rqst_replace_page(struct svc_rqst *rqstp, struct page *page)
> > +int 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];
>=20
> Would it make sense to use rq_page_end here? Just a thought.
>=20

That should be set to the right value, but do you trust that it wouldn't
be corrupt if rq_pages got overrun? It's only 3 pointers beyond the end
of the array. This should work even if rq_page_end gets clobbered.

>=20
> > +	if (WARN_ON_ONCE(rqstp->rq_next_page < begin || rqstp->rq_next_page >=
 end))
> > +		return -EIO;
> > +
> > 	if (*rqstp->rq_next_page) {
> > 		if (!pagevec_space(&rqstp->rq_pvec))
> > 			__pagevec_release(&rqstp->rq_pvec);
> > @@ -853,6 +864,7 @@ void svc_rqst_replace_page(struct svc_rqst *rqstp, =
struct page *page)
> >=20
> > 	get_page(page);
> > 	*(rqstp->rq_next_page++) =3D page;
> > +	return 0;
> > }
> > EXPORT_SYMBOL_GPL(svc_rqst_replace_page);
> >=20
> > --=20
> > 2.39.2
> >=20
>=20
> --
> Chuck Lever
>=20
>=20

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