RPCSEC_GSS: Fix an Oopsable condition when creating/destroying pipefs objects

If an error condition occurs on rpc_pipefs creation, or the user mounts
rpc_pipefs and then unmounts it, then the dentries in struct gss_auth
need to be reset to NULL so that a second call to gss_pipes_dentries_destroy
doesn't try to free them again.
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

net/sunrpc/auth_gss/auth_gss.c

@@ -796,10 +796,14 @@ static void gss_pipes_dentries_destroy(struct rpc_auth *auth)
 	struct gss_auth *gss_auth;
 
 	gss_auth = container_of(auth, struct gss_auth, rpc_auth);
-	if (gss_auth->pipe[0]->dentry)
+	if (gss_auth->pipe[0]->dentry) {
 		rpc_unlink(gss_auth->pipe[0]->dentry);
-	if (gss_auth->pipe[1]->dentry)
+		gss_auth->pipe[0]->dentry = NULL;
+	}
+	if (gss_auth->pipe[1]->dentry) {
 		rpc_unlink(gss_auth->pipe[1]->dentry);
+		gss_auth->pipe[1]->dentry = NULL;
+	}
 }
 
 static int gss_pipes_dentries_create(struct rpc_auth *auth)
@@ -807,26 +811,30 @@ static int gss_pipes_dentries_create(struct rpc_auth *auth)
 	int err;
 	struct gss_auth *gss_auth;
 	struct rpc_clnt *clnt;
+	struct dentry *dentry;
 
 	gss_auth = container_of(auth, struct gss_auth, rpc_auth);
 	clnt = gss_auth->client;
 
-	gss_auth->pipe[1]->dentry = rpc_mkpipe_dentry(clnt->cl_dentry,
-						      "gssd",
+	dentry = rpc_mkpipe_dentry(clnt->cl_dentry, "gssd",
 			clnt, gss_auth->pipe[1]);
-	if (IS_ERR(gss_auth->pipe[1]->dentry))
-		return PTR_ERR(gss_auth->pipe[1]->dentry);
-	gss_auth->pipe[0]->dentry = rpc_mkpipe_dentry(clnt->cl_dentry,
-						      gss_auth->mech->gm_name,
+	if (IS_ERR(dentry)) {
+		err = PTR_ERR(dentry);
+		goto err;
+	}
+	gss_auth->pipe[1]->dentry = dentry;
+	dentry = rpc_mkpipe_dentry(clnt->cl_dentry, gss_auth->mech->gm_name,
 			clnt, gss_auth->pipe[0]);
-	if (IS_ERR(gss_auth->pipe[0]->dentry)) {
-		err = PTR_ERR(gss_auth->pipe[0]->dentry);
+	if (IS_ERR(dentry)) {
+		err = PTR_ERR(dentry);
 		goto err_unlink_pipe_1;
 	}
 	return 0;
 
 err_unlink_pipe_1:
 	rpc_unlink(gss_auth->pipe[1]->dentry);
+	gss_auth->pipe[1]->dentry = NULL;
+err:
 	return err;
 }