NFSv4: Fix security auto-negotiation

NFSv4 security auto-negotiation has been broken since
commit 4580a92d (NFS:
Use server-recommended security flavor by default (NFSv3))
because nfs4_try_mount() will automatically select AUTH_SYS
if it sees no auth flavours.
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
Cc: Chuck Lever <chuck.lever@oracle.com>

fs/nfs/internal.h

@@ -358,7 +358,7 @@ extern struct dentry *nfs_get_root(struct super_block *, struct nfs_fh *,
 extern struct dentry *nfs4_get_root(struct super_block *, struct nfs_fh *,
 				    const char *);
 
-extern int nfs4_get_rootfh(struct nfs_server *server, struct nfs_fh *mntfh);
+extern int nfs4_get_rootfh(struct nfs_server *server, struct nfs_fh *mntfh, bool);
 #endif
 
 struct nfs_pgio_completion_ops;

fs/nfs/nfs4_fs.h

@@ -221,7 +221,7 @@ struct vfsmount *nfs4_submount(struct nfs_server *, struct dentry *,
 /* nfs4proc.c */
 extern int nfs4_proc_setclientid(struct nfs_client *, u32, unsigned short, struct rpc_cred *, struct nfs4_setclientid_res *);
 extern int nfs4_proc_setclientid_confirm(struct nfs_client *, struct nfs4_setclientid_res *arg, struct rpc_cred *);
-extern int nfs4_proc_get_rootfh(struct nfs_server *, struct nfs_fh *, struct nfs_fsinfo *);
+extern int nfs4_proc_get_rootfh(struct nfs_server *, struct nfs_fh *, struct nfs_fsinfo *, bool);
 extern int nfs4_proc_bind_conn_to_session(struct nfs_client *, struct rpc_cred *cred);
 extern int nfs4_proc_exchange_id(struct nfs_client *clp, struct rpc_cred *cred);
 extern int nfs4_destroy_clientid(struct nfs_client *clp);

fs/nfs/nfs4client.c

@@ -885,7 +885,7 @@ static void nfs4_session_set_rwsize(struct nfs_server *server)
 }
 
 static int nfs4_server_common_setup(struct nfs_server *server,
-		struct nfs_fh *mntfh)
+		struct nfs_fh *mntfh, bool auth_probe)
 {
 	struct nfs_fattr *fattr;
 	int error;
@@ -917,7 +917,7 @@ static int nfs4_server_common_setup(struct nfs_server *server,
 
 
 	/* Probe the root fh to retrieve its FSID and filehandle */
-	error = nfs4_get_rootfh(server, mntfh);
+	error = nfs4_get_rootfh(server, mntfh, auth_probe);
 	if (error < 0)
 		goto out;
 
@@ -949,6 +949,7 @@ static int nfs4_server_common_setup(struct nfs_server *server,
 static int nfs4_init_server(struct nfs_server *server,
 		const struct nfs_parsed_mount_data *data)
 {
+	rpc_authflavor_t pseudoflavor = RPC_AUTH_UNIX;
 	struct rpc_timeout timeparms;
 	int error;
 
@@ -961,13 +962,16 @@ static int nfs4_init_server(struct nfs_server *server,
 	server->flags = data->flags;
 	server->options = data->options;
 
+	if (data->auth_flavor_len >= 1)
+		pseudoflavor = data->auth_flavors[0];
+
 	/* Get a client record */
 	error = nfs4_set_client(server,
 			data->nfs_server.hostname,
 			(const struct sockaddr *)&data->nfs_server.address,
 			data->nfs_server.addrlen,
 			data->client_address,
-			data->auth_flavors[0],
+			pseudoflavor,
 			data->nfs_server.protocol,
 			&timeparms,
 			data->minorversion,
@@ -987,7 +991,7 @@ static int nfs4_init_server(struct nfs_server *server,
 
 	server->port = data->nfs_server.port;
 
-	error = nfs_init_server_rpcclient(server, &timeparms, data->auth_flavors[0]);
+	error = nfs_init_server_rpcclient(server, &timeparms, pseudoflavor);
 
 error:
 	/* Done */
@@ -1005,6 +1009,7 @@ struct nfs_server *nfs4_create_server(struct nfs_mount_info *mount_info,
 				      struct nfs_subversion *nfs_mod)
 {
 	struct nfs_server *server;
+	bool auth_probe;
 	int error;
 
 	dprintk("--> nfs4_create_server()\n");
@@ -1013,12 +1018,14 @@ struct nfs_server *nfs4_create_server(struct nfs_mount_info *mount_info,
 	if (!server)
 		return ERR_PTR(-ENOMEM);
 
+	auth_probe = mount_info->parsed->auth_flavor_len < 1;
+
 	/* set up the general RPC client */
 	error = nfs4_init_server(server, mount_info->parsed);
 	if (error < 0)
 		goto error;
 
-	error = nfs4_server_common_setup(server, mount_info->mntfh);
+	error = nfs4_server_common_setup(server, mount_info->mntfh, auth_probe);
 	if (error < 0)
 		goto error;
 
@@ -1071,7 +1078,7 @@ struct nfs_server *nfs4_create_referral_server(struct nfs_clone_mount *data,
 	if (error < 0)
 		goto error;
 
-	error = nfs4_server_common_setup(server, mntfh);
+	error = nfs4_server_common_setup(server, mntfh, false);
 	if (error < 0)
 		goto error;
 

fs/nfs/nfs4getroot.c

@@ -9,7 +9,7 @@
 
 #define NFSDBG_FACILITY		NFSDBG_CLIENT
 
-int nfs4_get_rootfh(struct nfs_server *server, struct nfs_fh *mntfh)
+int nfs4_get_rootfh(struct nfs_server *server, struct nfs_fh *mntfh, bool auth_probe)
 {
 	struct nfs_fsinfo fsinfo;
 	int ret = -ENOMEM;
@@ -21,7 +21,7 @@ int nfs4_get_rootfh(struct nfs_server *server, struct nfs_fh *mntfh)
 		goto out;
 
 	/* Start by getting the root filehandle from the server */
-	ret = nfs4_proc_get_rootfh(server, mntfh, &fsinfo);
+	ret = nfs4_proc_get_rootfh(server, mntfh, &fsinfo, auth_probe);
 	if (ret < 0) {
 		dprintk("nfs4_get_rootfh: getroot error = %d\n", -ret);
 		goto out;

fs/nfs/nfs4proc.c

@@ -2884,18 +2884,27 @@ static int nfs4_do_find_root_sec(struct nfs_server *server,
  * @server: initialized nfs_server handle
  * @fhandle: we fill in the pseudo-fs root file handle
  * @info: we fill in an FSINFO struct
+ * @auth_probe: probe the auth flavours
  *
  * Returns zero on success, or a negative errno.
  */
 int nfs4_proc_get_rootfh(struct nfs_server *server, struct nfs_fh *fhandle,
-			 struct nfs_fsinfo *info)
+			 struct nfs_fsinfo *info,
+			 bool auth_probe)
 {
 	int status;
 
-	status = nfs4_lookup_root(server, fhandle, info);
-	if ((status == -NFS4ERR_WRONGSEC) &&
-	    !(server->flags & NFS_MOUNT_SECFLAVOUR))
+	switch (auth_probe) {
+	case false:
+		status = nfs4_lookup_root(server, fhandle, info);
+		if (status != -NFS4ERR_WRONGSEC)
+			break;
+		/* Did user force a 'sec=' mount option? */
+		if (server->flags & NFS_MOUNT_SECFLAVOUR)
+			break;
+	default:
 		status = nfs4_do_find_root_sec(server, fhandle, info);
+	}
 
 	if (status == 0)
 		status = nfs4_server_capabilities(server, fhandle);

fs/nfs/nfs4super.c

@@ -253,10 +253,6 @@ struct dentry *nfs4_try_mount(int flags, const char *dev_name,
 
 	dfprintk(MOUNT, "--> nfs4_try_mount()\n");
 
-	if (data->auth_flavor_len < 1) {
-		data->auth_flavors[0] = RPC_AUTH_UNIX;
-		data->auth_flavor_len = 1;
-	}
 	export_path = data->nfs_server.export_path;
 	data->nfs_server.export_path = "/";
 	root_mnt = nfs_do_root_mount(&nfs4_remote_fs_type, flags, mount_info,