[PATCH v6 4/5] SUNRPC: kmap() the xdr pages during decode

[Anna Schumaker <anna@kernel.org>]

From: Anna Schumaker <Anna.Schumaker@Netapp.com>

If the pages are in HIGHMEM then we need to make sure they're mapped
before trying to read data off of them, otherwise we could end up with a
NULL pointer dereference.

The downside to this is that we need an extra cleanup step at the end of
decode to kunmap() the last page. I introduced an xdr_finish_decode()
function to do this. Right now this function only calls the
unmap_current_page() function, but other generic cleanup steps could be
added in the future if we come across anything else.

Reported-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
---
 include/linux/sunrpc/xdr.h |  3 +++
 net/sunrpc/clnt.c          |  1 +
 net/sunrpc/svc.c           |  2 ++
 net/sunrpc/xdr.c           | 27 ++++++++++++++++++++++++++-
 4 files changed, 32 insertions(+), 1 deletion(-)

diff --git a/include/linux/sunrpc/xdr.h b/include/linux/sunrpc/xdr.h
index 6bffd10b7a33..b75b3d416c5c 100644
--- a/include/linux/sunrpc/xdr.h
+++ b/include/linux/sunrpc/xdr.h
@@ -228,6 +228,7 @@ struct xdr_stream {
 	struct kvec *iov;	/* pointer to the current kvec */
 	struct kvec scratch;	/* Scratch buffer */
 	struct page **page_ptr;	/* pointer to the current page */
+	void *page_kaddr;	/* kmapped address of the current page */
 	unsigned int nwords;	/* Remaining decode buffer length */
 
 	struct rpc_rqst *rqst;	/* For debugging */
@@ -253,12 +254,14 @@ extern void xdr_truncate_decode(struct xdr_stream *xdr, size_t len);
 extern int xdr_restrict_buflen(struct xdr_stream *xdr, int newbuflen);
 extern void xdr_write_pages(struct xdr_stream *xdr, struct page **pages,
 		unsigned int base, unsigned int len);
+extern void xdr_stream_unmap_current_page(struct xdr_stream *xdr);
 extern unsigned int xdr_stream_pos(const struct xdr_stream *xdr);
 extern unsigned int xdr_page_pos(const struct xdr_stream *xdr);
 extern void xdr_init_decode(struct xdr_stream *xdr, struct xdr_buf *buf,
 			    __be32 *p, struct rpc_rqst *rqst);
 extern void xdr_init_decode_pages(struct xdr_stream *xdr, struct xdr_buf *buf,
 		struct page **pages, unsigned int len);
+extern void xdr_finish_decode(struct xdr_stream *xdr);
 extern __be32 *xdr_inline_decode(struct xdr_stream *xdr, size_t nbytes);
 extern unsigned int xdr_read_pages(struct xdr_stream *xdr, unsigned int len);
 extern void xdr_enter_page(struct xdr_stream *xdr, unsigned int len);
diff --git a/net/sunrpc/clnt.c b/net/sunrpc/clnt.c
index d7c697af3762..ca2c6efe19c9 100644
--- a/net/sunrpc/clnt.c
+++ b/net/sunrpc/clnt.c
@@ -2602,6 +2602,7 @@ call_decode(struct rpc_task *task)
 	case 0:
 		task->tk_action = rpc_exit_task;
 		task->tk_status = rpcauth_unwrap_resp(task, &xdr);
+		xdr_finish_decode(&xdr);
 		return;
 	case -EAGAIN:
 		task->tk_status = 0;
diff --git a/net/sunrpc/svc.c b/net/sunrpc/svc.c
index 587811a002c9..a864414ce811 100644
--- a/net/sunrpc/svc.c
+++ b/net/sunrpc/svc.c
@@ -1370,6 +1370,8 @@ svc_process_common(struct svc_rqst *rqstp)
 	rc = process.dispatch(rqstp);
 	if (procp->pc_release)
 		procp->pc_release(rqstp);
+	xdr_finish_decode(xdr);
+
 	if (!rc)
 		goto dropit;
 	if (rqstp->rq_auth_stat != rpc_auth_ok)
diff --git a/net/sunrpc/xdr.c b/net/sunrpc/xdr.c
index 94bddd1dd1d7..d318701a904a 100644
--- a/net/sunrpc/xdr.c
+++ b/net/sunrpc/xdr.c
@@ -1306,6 +1306,14 @@ static unsigned int xdr_set_tail_base(struct xdr_stream *xdr,
 	return xdr_set_iov(xdr, buf->tail, base, len);
 }
 
+void xdr_stream_unmap_current_page(struct xdr_stream *xdr)
+{
+	if (xdr->page_kaddr) {
+		kunmap_local(xdr->page_kaddr);
+		xdr->page_kaddr = NULL;
+	}
+}
+
 static unsigned int xdr_set_page_base(struct xdr_stream *xdr,
 				      unsigned int base, unsigned int len)
 {
@@ -1323,12 +1331,18 @@ static unsigned int xdr_set_page_base(struct xdr_stream *xdr,
 	if (len > maxlen)
 		len = maxlen;
 
+	xdr_stream_unmap_current_page(xdr);
 	xdr_stream_page_set_pos(xdr, base);
 	base += xdr->buf->page_base;
 
 	pgnr = base >> PAGE_SHIFT;
 	xdr->page_ptr = &xdr->buf->pages[pgnr];
-	kaddr = page_address(*xdr->page_ptr);
+
+	if (PageHighMem(*xdr->page_ptr)) {
+		xdr->page_kaddr = kmap_local_page(*xdr->page_ptr);
+		kaddr = xdr->page_kaddr;
+	} else
+		kaddr = page_address(*xdr->page_ptr);
 
 	pgoff = base & ~PAGE_MASK;
 	xdr->p = (__be32*)(kaddr + pgoff);
@@ -1382,6 +1396,7 @@ void xdr_init_decode(struct xdr_stream *xdr, struct xdr_buf *buf, __be32 *p,
 		     struct rpc_rqst *rqst)
 {
 	xdr->buf = buf;
+	xdr->page_kaddr = NULL;
 	xdr_reset_scratch_buffer(xdr);
 	xdr->nwords = XDR_QUADLEN(buf->len);
 	if (xdr_set_iov(xdr, buf->head, 0, buf->len) == 0 &&
@@ -1414,6 +1429,16 @@ void xdr_init_decode_pages(struct xdr_stream *xdr, struct xdr_buf *buf,
 }
 EXPORT_SYMBOL_GPL(xdr_init_decode_pages);
 
+/**
+ * xdr_finish_decode - Clean up the xdr_stream after decoding data.
+ * @xdr: pointer to xdr_stream struct
+ */
+void xdr_finish_decode(struct xdr_stream *xdr)
+{
+	xdr_stream_unmap_current_page(xdr);
+}
+EXPORT_SYMBOL(xdr_finish_decode);
+
 static __be32 * __xdr_inline_decode(struct xdr_stream *xdr, size_t nbytes)
 {
 	unsigned int nwords = XDR_QUADLEN(nbytes);
-- 
2.41.0