NFS: Handle a zero-length auth flavor list
Some releases of Linux rpc.mountd (nfs-utils 1.1.4 and later) return an
empty auth flavor list if no sec= was specified for the export. This is
notably broken server behavior.
The new auth flavor list checking added in a recent commit rejects this
case. The OpenSolaris client does too.
The broken mountd implementation is already widely deployed. To avoid
a behavioral regression, the kernel's mount client skips flavor checking
(ie reverts to the pre-2.6.32 behavior) if mountd returns an empty
flavor list.
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
diff --git a/fs/nfs/super.c b/fs/nfs/super.c
index 9c85cdb..f3a95df 100644
--- a/fs/nfs/super.c
+++ b/fs/nfs/super.c
@@ -1338,6 +1338,16 @@
unsigned int i, j, server_authlist_len = *(request->auth_flav_len);
/*
+ * Certain releases of Linux's mountd return an empty
+ * flavor list. To prevent behavioral regression with
+ * these servers (ie. rejecting mounts that used to
+ * succeed), revert to pre-2.6.32 behavior (no checking)
+ * if the returned flavor list is empty.
+ */
+ if (server_authlist_len == 0)
+ return 0;
+
+ /*
* 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.