From 08e4c304cd33d33892a0435c9ee4a865fc915e8f Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Emmanuel=20Lepage=20Vall=C3=A9e?= <elv1313@gmail.com>
Date: Tue, 30 Aug 2016 06:59:45 -0400
Subject: [PATCH] client: Fix a potential crash due to a race condition.
 (#1055)

If raise was called from the awful.rule `manage` callback at
startup with a client already present it crashed due to a
buffer underflow.
---
 objects/client.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/objects/client.c b/objects/client.c
index ce81e9add..838112d18 100644
--- a/objects/client.c
+++ b/objects/client.c
@@ -2383,7 +2383,10 @@ luaA_client_raise(lua_State *L)
     client_t *c = luaA_checkudata(L, 1, &client_class);
 
     /* Avoid sending the signal if nothing was done */
-    if (c->transient_for == NULL && globalconf.stack.tab[globalconf.stack.len-1] == c)
+    if (c->transient_for == NULL &&
+        globalconf.stack.len &&
+        globalconf.stack.tab[globalconf.stack.len-1] == c
+    )
         return 0;
 
     client_raise(c);