1 files changed, 51 insertions, 7 deletions

diff --git a/fs/nfs/super.c b/fs/nfs/super.c
index a33e608713e9..8526008eba72 100644
--- a/fs/nfs/super.c
+++ b/fs/nfs/super.c
@@ -1437,13 +1437,50 @@ out_security_failure:
 }
 
 /*
+ * Match the requested auth flavors with the list returned by
+ * the server.  Returns zero and sets the mount's authentication
+ * flavor on success; returns -EACCES if server does not support
+ * the requested flavor.
+ */
+static int nfs_walk_authlist(struct nfs_parsed_mount_data *args,
+                             struct nfs_mount_request *request)
+{
+        unsigned int i, j, server_authlist_len = *(request->auth_flav_len);
+
+        /*
+         * We avoid sophisticated negotiating here, as there are
+         * plenty of cases where we can get it wrong, providing
+         * either too little or too much security.
+         *
+         * RFC 2623, section 2.7 suggests we SHOULD prefer the
+         * flavor listed first.  However, some servers list
+         * AUTH_NULL first.  Our caller plants AUTH_SYS, the
+         * preferred default, in args->auth_flavors[0] if user
+         * didn't specify sec= mount option.
+         */
+        for (i = 0; i < args->auth_flavor_len; i++)
+                for (j = 0; j < server_authlist_len; j++)
+                        if (args->auth_flavors[i] == request->auth_flavs[j]) {
+                                dfprintk(MOUNT, "NFS: using auth flavor %d\n",
+                                        request->auth_flavs[j]);
+                                args->auth_flavors[0] = request->auth_flavs[j];
+                                return 0;
+                        }
+
+        dfprintk(MOUNT, "NFS: server does not support requested auth flavor\n");
+        nfs_umount(request);
+        return -EACCES;
+}
+
+/*
  * Use the remote server's MOUNT service to request the NFS file handle
  * corresponding to the provided path.
  */
 static int nfs_try_mount(struct nfs_parsed_mount_data *args,
                          struct nfs_fh *root_fh)
 {
-        unsigned int auth_flavor_len = 0;
+        rpc_authflavor_t server_authlist[NFS_MAX_SECFLAVORS];
+        unsigned int server_authlist_len = ARRAY_SIZE(server_authlist);
         struct nfs_mount_request request = {
                 .sap            = (struct sockaddr *)
                                                 &args->mount_server.address,
@@ -1451,7 +1488,8 @@ static int nfs_try_mount(struct nfs_parsed_mount_data *args,
                 .protocol       = args->mount_server.protocol,
                 .fh             = root_fh,
                 .noresvport     = args->flags & NFS_MOUNT_NORESVPORT,
-                .auth_flav_len  = &auth_flavor_len,
+                .auth_flav_len  = &server_authlist_len,
+                .auth_flavs     = server_authlist,
         };
         int status;
 
@@ -1488,12 +1526,18 @@ static int nfs_try_mount(struct nfs_parsed_mount_data *args,
          * to a file handle.
          */
         status = nfs_mount(&request);
-        if (status == 0)
-                return 0;
+        if (status != 0) {
+                dfprintk(MOUNT, "NFS: unable to mount server %s, error %d\n",
+                                request.hostname, status);
+                return status;
+        }
 
-        dfprintk(MOUNT, "NFS: unable to mount server %s, error %d\n",
-                        request.hostname, status);
-        return status;
+        /*
+         * MNTv1 (NFSv2) does not support auth flavor negotiation.
+         */
+        if (args->mount_server.version != NFS_MNT3_VERSION)
+                return 0;
+        return nfs_walk_authlist(args, &request);
 }
 
 static int nfs_parse_simple_hostname(const char *dev_name,