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 13:13 -0400, Jeff Layton 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;

Oops, this will get the page_base wrong if the first splice covers
multiple pages. I'll need to respin the offset handling.

> +		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];
> +	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);
>  

-- 
Jeff Layton <jlayton@kernel.org>