nfsd4: fix discarded security labels on setattr

Security labels in setattr calls are currently ignored because we forget
to set label->len.

Cc: stable@vger.kernel.org
Reported-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>
diff --git a/fs/nfsd/nfs4xdr.c b/fs/nfsd/nfs4xdr.c
index 83db5a7..d9d7fa9 100644
--- a/fs/nfsd/nfs4xdr.c
+++ b/fs/nfsd/nfs4xdr.c
@@ -411,6 +411,7 @@
 		label->data = kzalloc(dummy32 + 1, GFP_KERNEL);
 		if (!label->data)
 			return nfserr_jukebox;
+		label->len = dummy32;
 		defer_free(argp, kfree, label->data);
 		memcpy(label->data, buf, dummy32);
 	}