NFS client bugfix for 3.12

- Fix a regression due to incorrect sharing of gss auth caches
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Merge tag 'nfs-for-3.12-3' of git://git.linux-nfs.org/projects/trondmy/linux-nfs

Pull NFS client bugfix from Trond Myklebust:
 "Fix a regression due to incorrect sharing of gss auth caches"

* tag 'nfs-for-3.12-3' of git://git.linux-nfs.org/projects/trondmy/linux-nfs:
  RPCSEC_GSS: fix crash on destroying gss auth

net/sunrpc/auth_gss/auth_gss.c

@@ -1075,6 +1075,15 @@ gss_destroy(struct rpc_auth *auth)
 	kref_put(&gss_auth->kref, gss_free_callback);
 }
 
+/*
+ * Auths may be shared between rpc clients that were cloned from a
+ * common client with the same xprt, if they also share the flavor and
+ * target_name.
+ *
+ * The auth is looked up from the oldest parent sharing the same
+ * cl_xprt, and the auth itself references only that common parent
+ * (which is guaranteed to last as long as any of its descendants).
+ */
 static struct gss_auth *
 gss_auth_find_or_add_hashed(struct rpc_auth_create_args *args,
 		struct rpc_clnt *clnt,
@@ -1088,6 +1097,8 @@ gss_auth_find_or_add_hashed(struct rpc_auth_create_args *args,
 			gss_auth,
 			hash,
 			hashval) {
+		if (gss_auth->client != clnt)
+			continue;
 		if (gss_auth->rpc_auth.au_flavor != args->pseudoflavor)
 			continue;
 		if (gss_auth->target_name != args->target_name) {