cifs: add NULL check for ses->tcon_ipc

In some scenarios (DFS and BAD_NETWORK_NAME) set_root_set() can be
called with a NULL ses->tcon_ipc.
Signed-off-by: Aurelien Aptel <aaptel@suse.com>
Reviewed-by: Paulo Alcantara (SUSE) <pc@cjr.nz>
CC: Stable <stable@vger.kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>

fs/cifs/connect.c

@@ -4546,7 +4546,8 @@ static void set_root_ses(struct cifs_sb_info *cifs_sb, struct cifs_ses *ses,
 	if (ses) {
 		spin_lock(&cifs_tcp_ses_lock);
 		ses->ses_count++;
-		ses->tcon_ipc->remap = cifs_remap(cifs_sb);
+		if (ses->tcon_ipc)
+			ses->tcon_ipc->remap = cifs_remap(cifs_sb);
 		spin_unlock(&cifs_tcp_ses_lock);
 	}
 	*root_ses = ses;