smb3: use netname when available on secondary channels

Some servers do not allow null netname contexts, which would cause
multichannel to revert to single channel when mounting to some
servers (e.g. Azure xSMB). The previous patch fixed that by avoiding
incorrectly sending the netname context when there would be a null
hostname sent in the netname context, while this patch fixes the null
hostname for the secondary channel by using the hostname of the
primary channel for the secondary channel.

Fixes: 4c14d704 ("cifs: populate empty hostnames for extra channels")
Signed-off-by: Shyam Prasad N <sprasad@microsoft.com>
Reviewed-by: Paulo Alcantara (SUSE) <pc@cjr.nz>
Signed-off-by: Steve French <stfrench@microsoft.com>

fs/cifs/smb2pdu.c

@@ -543,6 +543,7 @@ assemble_neg_contexts(struct smb2_negotiate_req *req,
 		      struct TCP_Server_Info *server, unsigned int *total_len)
 {
 	char *pneg_ctxt;
+	char *hostname = NULL;
 	unsigned int ctxt_len, neg_context_count;
 
 	if (*total_len > 200) {
@@ -574,9 +575,15 @@ assemble_neg_contexts(struct smb2_negotiate_req *req,
 	*total_len += sizeof(struct smb2_posix_neg_context);
 	pneg_ctxt += sizeof(struct smb2_posix_neg_context);
 
-	if (server->hostname && (server->hostname[0] != 0)) {
+	/*
+	 * secondary channels don't have the hostname field populated
+	 * use the hostname field in the primary channel instead
+	 */
+	hostname = CIFS_SERVER_IS_CHAN(server) ?
+		server->primary_server->hostname : server->hostname;
+	if (hostname && (hostname[0] != 0)) {
 		ctxt_len = build_netname_ctxt((struct smb2_netname_neg_context *)pneg_ctxt,
-					server->hostname);
+					      hostname);
 		*total_len += ctxt_len;
 		pneg_ctxt += ctxt_len;
 		neg_context_count = 4;