Re: [PATCH v2 2/2] sunrpc: add bounds checking to svc_rqst_replace_page

[Jeff Layton <jlayton@kernel.org>]

On Fri, 2023-03-17 at 18:32 +0000, Chuck Lever III wrote:
> 
> > On Mar 17, 2023, at 1:13 PM, Jeff Layton <jlayton@kernel.org> wrote:
> > 
> > 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.
> > 
> > Fix up nfsd_splice_actor (the only caller) to handle this case by either
> > returning an error or a short splice when this happens.
> > 
> > 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(-)
> > 
> > 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, struct pipe_buffer *buf,
> > 	struct page *page = buf->page;	// may be a compound one
> > 	unsigned offset = buf->offset;
> > 	struct page *last_page;
> > +	int ret = 0, consumed = 0;
> > 
> > 	last_page = page + (offset + sd->len - 1) / PAGE_SIZE;
> > 	for (page += offset / PAGE_SIZE; page <= last_page; page++) {
> > @@ -946,13 +947,23 @@ nfsd_splice_actor(struct pipe_inode_info *pipe, struct pipe_buffer *buf,
> > 		 * Skip page replacement when extending the contents
> > 		 * of the current page.
> > 		 */
> > -		if (page != *(rqstp->rq_next_page - 1))
> > -			svc_rqst_replace_page(rqstp, page);
> > +		if (page != *(rqstp->rq_next_page - 1)) {
> > +			ret = svc_rqst_replace_page(rqstp, page);
> > +			if (ret)
> > +				break;
> > +		}
> > +		consumed += min_t(int,
> > +				  PAGE_SIZE - offset_in_page(offset),
> > +				  sd->len - consumed);
> > +		offset = 0;
> > 	}
> > -	if (rqstp->rq_res.page_len == 0)	// first call
> > -		rqstp->rq_res.page_base = offset % PAGE_SIZE;
> > -	rqstp->rq_res.page_len += sd->len;
> > -	return sd->len;
> > +	if (consumed) {
> > +		if (rqstp->rq_res.page_len == 0)	// first call
> > +			rqstp->rq_res.page_base = offset % PAGE_SIZE;
> > +		rqstp->rq_res.page_len += consumed;
> > +		return consumed;
> > +	}
> > +	return ret;
> > }
> > 
> > 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 *, unsigned 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 = rqstp->rq_pages;
> > +	end = &rqstp->rq_pages[RPCSVC_MAXPAGES];
> 
> Would it make sense to use rq_page_end here? Just a thought.
> 

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.

> 
> > +	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)
> > 
> > 	get_page(page);
> > 	*(rqstp->rq_next_page++) = page;
> > +	return 0;
> > }
> > EXPORT_SYMBOL_GPL(svc_rqst_replace_page);
> > 
> > -- 
> > 2.39.2
> > 
> 
> --
> Chuck Lever
> 
> 

-- 
Jeff Layton <jlayton@kernel.org>