cifs: do not include page data when checking signature

On async reads, page data is allocated before sending.  When the
response is received but it has no data to fill (e.g.
STATUS_END_OF_FILE), __calc_signature() will still include the pages in
its computation, leading to an invalid signature check.

This patch fixes this by not setting the async read smb_rqst page data
(zeroed by default) if its got_bytes is 0.

This can be reproduced/verified with xfstests generic/465.

Cc: <stable@vger.kernel.org>
Signed-off-by: Enzo Matsumiya <ematsumiya@suse.de>
Reviewed-by: Paulo Alcantara (SUSE) <pc@cjr.nz>
Signed-off-by: Steve French <stfrench@microsoft.com>

fs/cifs/smb2pdu.c

@@ -4163,12 +4163,15 @@ smb2_readv_callback(struct mid_q_entry *mid)
 				(struct smb2_hdr *)rdata->iov[0].iov_base;
 	struct cifs_credits credits = { .value = 0, .instance = 0 };
 	struct smb_rqst rqst = { .rq_iov = &rdata->iov[1],
-				 .rq_nvec = 1,
-				 .rq_pages = rdata->pages,
-				 .rq_offset = rdata->page_offset,
-				 .rq_npages = rdata->nr_pages,
-				 .rq_pagesz = rdata->pagesz,
-				 .rq_tailsz = rdata->tailsz };
+				 .rq_nvec = 1, };
+
+	if (rdata->got_bytes) {
+		rqst.rq_pages = rdata->pages;
+		rqst.rq_offset = rdata->page_offset;
+		rqst.rq_npages = rdata->nr_pages;
+		rqst.rq_pagesz = rdata->pagesz;
+		rqst.rq_tailsz = rdata->tailsz;
+	}
 
 	WARN_ONCE(rdata->server != mid->server,
 		  "rdata server %p != mid server %p",