NFS: avoid NULL dereference in nfs_destroy_server

commit f259613a1e4b44a0cf85a5dafd931be96ee7c9e5 upstream.

In rare circumstances, nfs_clone_server() of a v2 or v3 server can get
an error between setting server->destory (to nfs_destroy_server), and
calling nfs_start_lockd (which will set server->nlm_host).

If this happens, nfs_clone_server will call nfs_free_server which
will call nfs_destroy_server and thence nlmclnt_done(NULL).  This
causes the NULL to be dereferenced.

So add a guard to only call nlmclnt_done() if ->nlm_host is not NULL.

The other guards there are irrelevant as nlm_host can only be non-NULL
if one of these flags are set - so remove those tests.  (Thanks to Trond
for this suggestion).

This is suitable for any stable kernel since 2.6.25.

Signed-off-by: NeilBrown <neilb@suse.de>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/fs/nfs/client.c b/fs/nfs/client.c
index 873bf00d51a2b8d000ef9d45bdb9f139186ec6e5..d03a40019f9fafccc91c473827c41bfc0311fa95 100644 (file)
--- a/fs/nfs/client.c
+++ b/fs/nfs/client.c
@@ -672,8 +672,7 @@ static int nfs_create_rpc_client(struct nfs_client *clp,
  */
 static void nfs_destroy_server(struct nfs_server *server)
 {
-       if (!(server->flags & NFS_MOUNT_LOCAL_FLOCK) ||
-                       !(server->flags & NFS_MOUNT_LOCAL_FCNTL))
+       if (server->nlm_host)
                nlmclnt_done(server->nlm_host);
 }