sunrpc: correct the computation for page_ptr when truncating

BugLink: https://bugs.launchpad.net/bugs/1836802
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@redhat.com>
Cc: stable@vger.kernel.org
Signed-off-by: J. Bruce Fields <bfields@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>

diff --git a/net/sunrpc/xdr.c b/net/sunrpc/xdr.c
index e34f4ee7f2b6cecdf404daab0d3aab363d94ba01..13695ba8fc54047e510416838ea19be3d7e5d26b 100644 (file)
--- a/net/sunrpc/xdr.c
+++ b/net/sunrpc/xdr.c
@@ -639,11 +639,10 @@ void xdr_truncate_encode(struct xdr_stream *xdr, size_t len)
                WARN_ON_ONCE(xdr->iov);
                return;
        }
-       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;