SUNRPC: Ensure that gss_auth isn't freed before its upcall messages

commit 9eb2ddb4 upstream.

Fix a race in which the RPC client is shutting down while the
gss daemon is processing a downcall. If the RPC client manages to
shut down before the gss daemon is done, then the struct gss_auth
used in gss_release_msg() may have already been freed.

Link: http://lkml.kernel.org/r/1392494917.71728.YahooMailNeo@web140002.mail.bf1.yahoo.comReported-by: John <da_audiophile@yahoo.com>
Reported-by: Borislav Petkov <bp@alien8.de>
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>

net/sunrpc/auth_gss/auth_gss.c

@@ -108,6 +108,7 @@ struct gss_auth {
 static DEFINE_SPINLOCK(pipe_version_lock);
 static struct rpc_wait_queue pipe_version_rpc_waitqueue;
 static DECLARE_WAIT_QUEUE_HEAD(pipe_version_waitqueue);
+static void gss_put_auth(struct gss_auth *gss_auth);
 
 static void gss_free_ctx(struct gss_cl_ctx *);
 static const struct rpc_pipe_ops gss_upcall_ops_v0;
@@ -320,6 +321,7 @@ gss_release_msg(struct gss_upcall_msg *gss_msg)
 	if (gss_msg->ctx != NULL)
 		gss_put_ctx(gss_msg->ctx);
 	rpc_destroy_wait_queue(&gss_msg->rpc_waitqueue);
+	gss_put_auth(gss_msg->auth);
 	kfree(gss_msg);
 }
 
@@ -486,6 +488,7 @@ gss_alloc_msg(struct gss_auth *gss_auth,
 	default:
 		gss_encode_v1_msg(gss_msg, service_name, gss_auth->target_name);
 	};
+	kref_get(&gss_auth->kref);
 	return gss_msg;
 }
 
@@ -1052,6 +1055,12 @@ gss_free_callback(struct kref *kref)
 	gss_free(gss_auth);
 }
 
+static void
+gss_put_auth(struct gss_auth *gss_auth)
+{
+	kref_put(&gss_auth->kref, gss_free_callback);
+}
+
 static void
 gss_destroy(struct rpc_auth *auth)
 {
@@ -1073,7 +1082,7 @@ gss_destroy(struct rpc_auth *auth)
 	gss_auth->gss_pipe[1] = NULL;
 	rpcauth_destroy_credcache(auth);
 
-	kref_put(&gss_auth->kref, gss_free_callback);
+	gss_put_auth(gss_auth);
 }
 
 /*
@@ -1244,7 +1253,7 @@ gss_destroy_nullcred(struct rpc_cred *cred)
 	call_rcu(&cred->cr_rcu, gss_free_cred_callback);
 	if (ctx)
 		gss_put_ctx(ctx);
-	kref_put(&gss_auth->kref, gss_free_callback);
+	gss_put_auth(gss_auth);
 }
 
 static void