[PATCH 3.16.y-ckt 022/126] rpc: fix xdr_truncate_encode to handle buffer ending on page boundary

[Luis Henriques]

3.16.7-ckt5 -stable review patch.  If anyone has any objections, please let me know.

------------------

From: "J. Bruce Fields" <bfields at redhat.com>

commit 49a068f82a1d30eb585d7804b05948376be6cf9a upstream.

A struct xdr_stream at a page boundary might point to the end of one
page or the beginning of the next, but xdr_truncate_encode isn't
prepared to handle the former.

This can cause corruption of NFSv4 READDIR replies in the case that a
readdir entry that would have exceeded the client's dircount/maxcount
limit would have ended exactly on a 4k page boundary.  You're more
likely to hit this case on large directories.

Other xdr_truncate_encode callers are probably also affected.

Reported-by: Holger Hoffstätte <holger.hoffstaette at googlemail.com>
Tested-by: Holger Hoffstätte <holger.hoffstaette at googlemail.com>
Fixes: 3e19ce762b53 "rpc: xdr_truncate_encode"
Signed-off-by: J. Bruce Fields <bfields at redhat.com>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 net/sunrpc/xdr.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/net/sunrpc/xdr.c b/net/sunrpc/xdr.c
index 23fb4e75e245..25ef792dfee6 100644
--- a/net/sunrpc/xdr.c
+++ b/net/sunrpc/xdr.c
@@ -605,7 +605,7 @@ void xdr_truncate_encode(struct xdr_stream *xdr, size_t len)
 	struct kvec *head = buf->head;
 	struct kvec *tail = buf->tail;
 	int fraglen;
-	int new, old;
+	int new;
 
 	if (len > buf->len) {
 		WARN_ON_ONCE(1);
@@ -627,8 +627,8 @@ void xdr_truncate_encode(struct xdr_stream *xdr, size_t len)
 	buf->len -= fraglen;
 
 	new = buf->page_base + buf->page_len;
-	old = new + fraglen;
-	xdr->page_ptr -= (old >> PAGE_SHIFT) - (new >> PAGE_SHIFT);
+
+	xdr->page_ptr = buf->pages + (new >> PAGE_SHIFT);
 
 	if (buf->page_len && buf->len == len) {
 		xdr->p = page_address(*xdr->page_ptr);
-- 
2.1.4