[PATCH v1 0/3] rq_pages bounds checking

[PATCH v1 0/3] rq_pages bounds checking

[Chuck Lever]

A slightly modified take on Jeff's earlier patches, tested with
both NFSv3 and NFSv4.1 via simple fault injection in
svc_rqst_replace_page().

In general I'm in favor of more rq_pages bounds checking by
replacing direct modification of the rq_respages and rq_next_page
fields with accessor functions.

---

Chuck Lever (2):
      SUNRPC: add bounds checking to svc_rqst_replace_page
      NFSD: Watch for rq_pages bounds checking errors in nfsd_splice_actor()

Jeff Layton (1):
      nfsd: don't replace page in rq_pages if it's a continuation of last page


 fs/nfsd/vfs.c                 | 15 +++++++++++++--
 include/linux/sunrpc/svc.h    |  2 +-
 include/trace/events/sunrpc.h | 25 +++++++++++++++++++++++++
 net/sunrpc/svc.c              | 15 ++++++++++++++-
 4 files changed, 53 insertions(+), 4 deletions(-)

--
Chuck Lever

[PATCH v1 1/3] nfsd: don't replace page in rq_pages if it's a continuation of last page

[Chuck Lever]

From: Jeff Layton <jlayton@kernel.org>

The splice read calls nfsd_splice_actor to put the pages containing file
data into the svc_rqst->rq_pages array. It's possible however to get a
splice result that only has a partial page at the end, if (e.g.) the
filesystem hands back a short read that doesn't cover the whole page.

nfsd_splice_actor will plop the partial page into its rq_pages array and
return. Then later, when nfsd_splice_actor is called again, the
remainder of the page may end up being filled out. At this point,
nfsd_splice_actor will put the page into the array _again_ corrupting
the reply. If this is done enough times, rq_next_page will overrun the
array and corrupt the trailing fields -- the rq_respages and
rq_next_page pointers themselves.

If we've already added the page to the array in the last pass, don't add
it to the array a second time when dealing with a splice continuation.
This was originally handled properly in nfsd_splice_actor, but commit
91e23b1c3982 ("NFSD: Clean up nfsd_splice_actor()") removed the check
for it.

Fixes: 91e23b1c3982 ("NFSD: Clean up nfsd_splice_actor()")
Cc: Al Viro <viro@zeniv.linux.org.uk>
Reported-by: Dario Lesca <d.lesca@solinos.it>
Tested-by: David Critch <dcritch@redhat.com>
Link: https://bugzilla.redhat.com/show_bug.cgi?id=2150630
Signed-off-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
---
 fs/nfsd/vfs.c |    9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/fs/nfsd/vfs.c b/fs/nfsd/vfs.c
index 502e1b7742db..5783209f17fc 100644
--- a/fs/nfsd/vfs.c
+++ b/fs/nfsd/vfs.c
@@ -941,8 +941,15 @@ nfsd_splice_actor(struct pipe_inode_info *pipe, struct pipe_buffer *buf,
 	struct page *last_page;
 
 	last_page = page + (offset + sd->len - 1) / PAGE_SIZE;
-	for (page += offset / PAGE_SIZE; page <= last_page; page++)
+	for (page += offset / PAGE_SIZE; page <= last_page; page++) {
+		/*
+		 * Skip page replacement when extending the contents
+		 * of the current page.
+		 */
+		if (page == *(rqstp->rq_next_page - 1))
+			continue;
 		svc_rqst_replace_page(rqstp, page);
+	}
 	if (rqstp->rq_res.page_len == 0)	// first call
 		rqstp->rq_res.page_base = offset % PAGE_SIZE;
 	rqstp->rq_res.page_len += sd->len;

[PATCH v1 2/3] SUNRPC: add bounds checking to svc_rqst_replace_page

[Chuck Lever]

From: Chuck Lever <chuck.lever@oracle.com>

There have been several bugs over the years where the NFSD splice
actor has attempted to write outside the rq_pages array.

Suggested-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
---
 include/linux/sunrpc/svc.h    |    2 +-
 include/trace/events/sunrpc.h |   25 +++++++++++++++++++++++++
 net/sunrpc/svc.c              |   15 ++++++++++++++-
 3 files changed, 40 insertions(+), 2 deletions(-)

diff --git a/include/linux/sunrpc/svc.h b/include/linux/sunrpc/svc.h
index 877891536c2f..f5af055280ff 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,
+bool		   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/include/trace/events/sunrpc.h b/include/trace/events/sunrpc.h
index 3ca54536f8f7..5a3bb42e1f50 100644
--- a/include/trace/events/sunrpc.h
+++ b/include/trace/events/sunrpc.h
@@ -1790,6 +1790,31 @@ DEFINE_EVENT(svc_rqst_status, svc_send,
 	TP_PROTO(const struct svc_rqst *rqst, int status),
 	TP_ARGS(rqst, status));
 
+TRACE_EVENT(svc_replace_page_err,
+	TP_PROTO(const struct svc_rqst *rqst),
+
+	TP_ARGS(rqst),
+	TP_STRUCT__entry(
+		SVC_RQST_ENDPOINT_FIELDS(rqst)
+
+		__field(const void *, begin)
+		__field(const void *, respages)
+		__field(const void *, nextpage)
+	),
+
+	TP_fast_assign(
+		SVC_RQST_ENDPOINT_ASSIGNMENTS(rqst);
+
+		__entry->begin = rqst->rq_pages;
+		__entry->respages = rqst->rq_respages;
+		__entry->nextpage = rqst->rq_next_page;
+	),
+
+	TP_printk(SVC_RQST_ENDPOINT_FORMAT " begin=%p respages=%p nextpage=%p",
+		SVC_RQST_ENDPOINT_VARARGS,
+		__entry->begin, __entry->respages, __entry->nextpage)
+);
+
 TRACE_EVENT(svc_stats_latency,
 	TP_PROTO(
 		const struct svc_rqst *rqst
diff --git a/net/sunrpc/svc.c b/net/sunrpc/svc.c
index fea7ce8fba14..633aa1eb476b 100644
--- a/net/sunrpc/svc.c
+++ b/net/sunrpc/svc.c
@@ -842,9 +842,21 @@ 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.
+ *
+ * Return values:
+ *   %true: page replaced
+ *   %false: array bounds checking failed
  */
-void svc_rqst_replace_page(struct svc_rqst *rqstp, struct page *page)
+bool svc_rqst_replace_page(struct svc_rqst *rqstp, struct page *page)
 {
+	struct page **begin = rqstp->rq_pages;
+	struct page **end = &rqstp->rq_pages[RPCSVC_MAXPAGES];
+
+	if (unlikely(rqstp->rq_next_page < begin || rqstp->rq_next_page > end)) {
+		trace_svc_replace_page_err(rqstp);
+		return false;
+	}
+
 	if (*rqstp->rq_next_page) {
 		if (!pagevec_space(&rqstp->rq_pvec))
 			__pagevec_release(&rqstp->rq_pvec);
@@ -853,6 +865,7 @@ void svc_rqst_replace_page(struct svc_rqst *rqstp, struct page *page)
 
 	get_page(page);
 	*(rqstp->rq_next_page++) = page;
+	return true;
 }
 EXPORT_SYMBOL_GPL(svc_rqst_replace_page);
 

[PATCH v1 3/3] NFSD: Watch for rq_pages bounds checking errors in nfsd_splice_actor()

[Chuck Lever]

From: Chuck Lever <chuck.lever@oracle.com>

This is a "should never happen" condition, but if for some reason
the pipe splice actor should attempt to walk past the end of
rq_pages, it needs to terminate the READ operation to prevent
corruption of the pointer addresses in the fields just beyond the
array.

A server crash is thus prevented. Since the code is not behaving,
the READ operation returns -EIO to the client. None of the READ
payload data can be trusted if the splice actor isn't operating as
expected.

Suggested-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
---
 fs/nfsd/vfs.c |    6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/fs/nfsd/vfs.c b/fs/nfsd/vfs.c
index 5783209f17fc..10aa68ca82ef 100644
--- a/fs/nfsd/vfs.c
+++ b/fs/nfsd/vfs.c
@@ -930,6 +930,9 @@ nfsd_open_verified(struct svc_rqst *rqstp, struct svc_fh *fhp, int may_flags,
  * Grab and keep cached pages associated with a file in the svc_rqst
  * so that they can be passed to the network sendmsg/sendpage routines
  * directly. They will be released after the sending has completed.
+ *
+ * Return values: Number of bytes consumed, or -EIO if there are no
+ * remaining pages in rqstp->rq_pages.
  */
 static int
 nfsd_splice_actor(struct pipe_inode_info *pipe, struct pipe_buffer *buf,
@@ -948,7 +951,8 @@ nfsd_splice_actor(struct pipe_inode_info *pipe, struct pipe_buffer *buf,
 		 */
 		if (page == *(rqstp->rq_next_page - 1))
 			continue;
-		svc_rqst_replace_page(rqstp, page);
+		if (unlikely(!svc_rqst_replace_page(rqstp, page)))
+			return -EIO;
 	}
 	if (rqstp->rq_res.page_len == 0)	// first call
 		rqstp->rq_res.page_base = offset % PAGE_SIZE;

Re: [PATCH v1 0/3] rq_pages bounds checking

[Jeff Layton]

On Fri, 2023-03-17 at 19:01 -0400, Chuck Lever wrote:
> A slightly modified take on Jeff's earlier patches, tested with
> both NFSv3 and NFSv4.1 via simple fault injection in
> svc_rqst_replace_page().
> 
> In general I'm in favor of more rq_pages bounds checking by
> replacing direct modification of the rq_respages and rq_next_page
> fields with accessor functions.
> 
> ---
> 
> Chuck Lever (2):
>       SUNRPC: add bounds checking to svc_rqst_replace_page
>       NFSD: Watch for rq_pages bounds checking errors in nfsd_splice_actor()
> 
> Jeff Layton (1):
>       nfsd: don't replace page in rq_pages if it's a continuation of last page
> 
> 
>  fs/nfsd/vfs.c                 | 15 +++++++++++++--
>  include/linux/sunrpc/svc.h    |  2 +-
>  include/trace/events/sunrpc.h | 25 +++++++++++++++++++++++++
>  net/sunrpc/svc.c              | 15 ++++++++++++++-
>  4 files changed, 53 insertions(+), 4 deletions(-)
> 
> --
> Chuck Lever
> 

Looks good, Chuck, thanks. You can add this to the last two:

Reviewed-by: Jeff Layton <jlayton@kernel.org>

Re: [PATCH v1 0/3] rq_pages bounds checking

[Chuck Lever III]

> On Mar 18, 2023, at 6:04 AM, Jeff Layton <jlayton@kernel.org> wrote:
> 
> On Fri, 2023-03-17 at 19:01 -0400, Chuck Lever wrote:
>> A slightly modified take on Jeff's earlier patches, tested with
>> both NFSv3 and NFSv4.1 via simple fault injection in
>> svc_rqst_replace_page().
>> 
>> In general I'm in favor of more rq_pages bounds checking by
>> replacing direct modification of the rq_respages and rq_next_page
>> fields with accessor functions.
>> 
>> ---
>> 
>> Chuck Lever (2):
>>      SUNRPC: add bounds checking to svc_rqst_replace_page
>>      NFSD: Watch for rq_pages bounds checking errors in nfsd_splice_actor()
>> 
>> Jeff Layton (1):
>>      nfsd: don't replace page in rq_pages if it's a continuation of last page
>> 
>> 
>> fs/nfsd/vfs.c                 | 15 +++++++++++++--
>> include/linux/sunrpc/svc.h    |  2 +-
>> include/trace/events/sunrpc.h | 25 +++++++++++++++++++++++++
>> net/sunrpc/svc.c              | 15 ++++++++++++++-
>> 4 files changed, 53 insertions(+), 4 deletions(-)
>> 
>> --
>> Chuck Lever
>> 
> 
> Looks good, Chuck, thanks. You can add this to the last two:
> 
> Reviewed-by: Jeff Layton <jlayton@kernel.org>

Excellent, thanks!

When I started I expected 3/3 to be more substantial, but since it's
just a handful of lines and the patch descriptions are about the same,
I'm going to squash 2/3 and 3/3 together.

Only question is whether to apply that to nfsd-next or nfsd-fixes.
Since it's a defensive change, I was thinking nfsd-next. Let me know
if you think it should get merged sooner.


--
Chuck Lever

Re: [PATCH v1 0/3] rq_pages bounds checking

[Jeff Layton]

On Sat, 2023-03-18 at 15:20 +0000, Chuck Lever III wrote:
> 
> > On Mar 18, 2023, at 6:04 AM, Jeff Layton <jlayton@kernel.org> wrote:
> > 
> > On Fri, 2023-03-17 at 19:01 -0400, Chuck Lever wrote:
> > > A slightly modified take on Jeff's earlier patches, tested with
> > > both NFSv3 and NFSv4.1 via simple fault injection in
> > > svc_rqst_replace_page().
> > > 
> > > In general I'm in favor of more rq_pages bounds checking by
> > > replacing direct modification of the rq_respages and rq_next_page
> > > fields with accessor functions.
> > > 
> > > ---
> > > 
> > > Chuck Lever (2):
> > >      SUNRPC: add bounds checking to svc_rqst_replace_page
> > >      NFSD: Watch for rq_pages bounds checking errors in nfsd_splice_actor()
> > > 
> > > Jeff Layton (1):
> > >      nfsd: don't replace page in rq_pages if it's a continuation of last page
> > > 
> > > 
> > > fs/nfsd/vfs.c                 | 15 +++++++++++++--
> > > include/linux/sunrpc/svc.h    |  2 +-
> > > include/trace/events/sunrpc.h | 25 +++++++++++++++++++++++++
> > > net/sunrpc/svc.c              | 15 ++++++++++++++-
> > > 4 files changed, 53 insertions(+), 4 deletions(-)
> > > 
> > > --
> > > Chuck Lever
> > > 
> > 
> > Looks good, Chuck, thanks. You can add this to the last two:
> > 
> > Reviewed-by: Jeff Layton <jlayton@kernel.org>
> 
> Excellent, thanks!
> 
> When I started I expected 3/3 to be more substantial, but since it's
> just a handful of lines and the patch descriptions are about the same,
> I'm going to squash 2/3 and 3/3 together.
> 
> Only question is whether to apply that to nfsd-next or nfsd-fixes.
> Since it's a defensive change, I was thinking nfsd-next. Let me know
> if you think it should get merged sooner.
> 

No, that sounds fine for those. Patch #1 needs to go in ASAP, of course.
-- 
Jeff Layton <jlayton@kernel.org>