On Fri, 2023-03-17 at 17:51 +0000, Chuck Lever III wrote:
> > On Mar 17, 2023, at 1:13 PM, Jeff Layton <jlayton@xxxxxxxxxx> 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.
>
> IMO it's not worth the extra complexity to return a short splice.
> This is a "should never happen" scenario in a hot I/O path. Let's
> keep this code as simple as possible, and use unlikely() for the
> error cases in both nfsd_splice_actor and svc_rqst_replace_page().
>
Are there any issues with just returning an error even though we have
successfully spliced some of the data into the buffer? I guess the
caller will just see an EIO or whatever instead of the short read in
that case?
> Also, since "nfsd_splice_actor ... [is] the only caller", a WARN_ON
> stack trace is not adding value. I still think a tracepoint is more
> appropriate. I suggest:
>
> trace_svc_replace_page_err(rqst);
>
>
Ok, I can look at adding a conditional tracepoint.
> > Signed-off-by: Jeff Layton <jlayton@xxxxxxxxxx>
> > ---
> > 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];
> > + 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@xxxxxxxxxx>
