[PATCH] knfsd: fix an NFSD bug with full sized, non-page-aligned reads.

NFSd assumes that largest number of pages that will be needed
for a request+response is 2+N where N pages is the size of the largest
permitted read/write request.  The '2' are 1 for the non-data part of
the request, and 1 for the non-data part of the reply.

However, when a read request is not page-aligned, and we choose to use
->sendfile to send it directly from the page cache, we may need N+1
pages to hold the whole reply.  This can overflow and array and cause
an Oops.

This patch increases size of the array for holding pages by one and
makes sure that entry is NULL when it is not in use.

Signed-off-by: Neil Brown <neilb@suse.de>
Signed-off-by: Chris Wright <chrisw@sous-sol.org>

1 files changed, 4 insertions, 1 deletions

diff --git a/include/linux/sunrpc/svc.h b/include/linux/sunrpc/svc.h
index 965d6c20086e..64f3d60c72af 100644
--- a/include/linux/sunrpc/svc.h
+++ b/include/linux/sunrpc/svc.h
@@ -144,8 +144,11 @@ extern u32 svc_max_payload(const struct svc_rqst *rqstp);
  *
  * Each request/reply pair can have at most one "payload", plus two pages,
  * one for the request, and one for the reply.
+ * We using ->sendfile to return read data, we might need one extra page
+ * if the request is not page-aligned.  So add another '1'.
  */
-#define RPCSVC_MAXPAGES		((RPCSVC_MAXPAYLOAD+PAGE_SIZE-1)/PAGE_SIZE + 2)
+#define RPCSVC_MAXPAGES		((RPCSVC_MAXPAYLOAD+PAGE_SIZE-1)/PAGE_SIZE \
+				+ 2 + 1)
 
 static inline u32 svc_getnl(struct kvec *iov)
 {