[PATCH 3.16 142/305] sunrpc: correct the computation for page_ptr when truncating

From: Ben Hutchings
Date: Sun Feb 03 2019 - 08:59:51 EST

3.16.63-rc1 review patch. If anyone has any objections, please let me know.


From: Frank Sorenson <sorenson@xxxxxxxxxx>

commit 5d7a5bcb67c70cbc904057ef52d3fcfeb24420bb upstream.

When truncating the encode buffer, the page_ptr is getting
advanced, causing the next page to be skipped while encoding.
The page is still included in the response, so the response
contains a page of bogus data.

We need to adjust the page_ptr backwards to ensure we encode
the next page into the correct place.

We saw this triggered when concurrent directory modifications caused
nfsd4_encode_direct_fattr() to return nfserr_noent, and the resulting
call to xdr_truncate_encode() corrupted the READDIR reply.

Signed-off-by: Frank Sorenson <sorenson@xxxxxxxxxx>
Signed-off-by: J. Bruce Fields <bfields@xxxxxxxxxx>
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
net/sunrpc/xdr.c | 5 ++---
1 file changed, 2 insertions(+), 3 deletions(-)

--- a/net/sunrpc/xdr.c
+++ b/net/sunrpc/xdr.c
@@ -637,11 +637,10 @@ void xdr_truncate_encode(struct xdr_stre
/* xdr->iov should already be NULL */
- if (fraglen) {
+ if (fraglen)
xdr->end = head->iov_base + head->iov_len;
- xdr->page_ptr--;
- }
/* (otherwise assume xdr->end is already set) */
+ xdr->page_ptr--;
head->iov_len = len;
buf->len = len;
xdr->p = head->iov_base + head->iov_len;