NFS: Fix NFSv2 security settings

For a while now any NFSv2 mount where sec= is specified uses
AUTH_NULL. If sec= is not specified, the mount uses AUTH_UNIX.
Commit e68fd7c8071d ("mount: use sec= that was specified on the
command line") attempted to address a very similar problem with
NFSv3, and should have fixed this too, but it has a bug.

The MNTv1 MNT procedure does not return a list of security flavors,
so our client makes up a list containing just AUTH_NULL. This should
enable nfs_verify_authflavors() to assign the sec= specified flavor,
but instead, it incorrectly sets it to AUTH_NULL.

I expect this would also be a problem for any NFSv3 server whose
MNTv3 MNT procedure returned a security flavor list containing only
AUTH_NULL.

Fixes: e68fd7c8071d ("mount: use sec= that was specified on ... ")
BugLink: https://bugzilla.linux-nfs.org/show_bug.cgi?id=310
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>

diff --git a/fs/nfs/super.c b/fs/nfs/super.c
index d828ef8..6b179af 100644 (file)
--- a/fs/nfs/super.c
+++ b/fs/nfs/super.c
@@ -1691,8 +1691,8 @@ static int nfs_verify_authflavors(struct nfs_parsed_mount_data *args,
                        rpc_authflavor_t *server_authlist, unsigned int count)
 {
        rpc_authflavor_t flavor = RPC_AUTH_MAXFLAVOR;
+       bool found_auth_null = false;
        unsigned int i;
-       int use_auth_null = false;
 
        /*
         * If the sec= mount option is used, the specified flavor or AUTH_NULL
@@ -1701,6 +1701,10 @@ static int nfs_verify_authflavors(struct nfs_parsed_mount_data *args,
         * AUTH_NULL has a special meaning when it's in the server list - it
         * means that the server will ignore the rpc creds, so any flavor
         * can be used but still use the sec= that was specified.
+        *
+        * Note also that the MNT procedure in MNTv1 does not return a list
+        * of supported security flavors. In this case, nfs_mount() fabricates
+        * a security flavor list containing just AUTH_NULL.
         */
        for (i = 0; i < count; i++) {
                flavor = server_authlist[i];
@@ -1709,11 +1713,11 @@ static int nfs_verify_authflavors(struct nfs_parsed_mount_data *args,
                        goto out;
 
                if (flavor == RPC_AUTH_NULL)
-                       use_auth_null = true;
+                       found_auth_null = true;
        }
 
-       if (use_auth_null) {
-               flavor = RPC_AUTH_NULL;
+       if (found_auth_null) {
+               flavor = args->auth_info.flavors[0];
                goto out;
        }