Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S943263AbcJaOER (ORCPT ); Mon, 31 Oct 2016 10:04:17 -0400 Received: from thejh.net ([37.221.195.125]:58921 "EHLO thejh.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S942333AbcJaOEQ (ORCPT ); Mon, 31 Oct 2016 10:04:16 -0400 From: Jann Horn To: Andrew Morton , Michal Hocko , Ingo Molnar , Andy Lutomirski , Kees Cook Cc: linux-kernel@vger.kernel.org, kernel-hardening@lists.openwall.com, Daniel Micay Subject: [PATCH] fork: make whole stack_canary random Date: Mon, 31 Oct 2016 15:04:01 +0100 Message-Id: <1477922641-2221-1-git-send-email-jann@thejh.net> X-Mailer: git-send-email 2.1.4 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1049 Lines: 31 On machines with sizeof(unsigned long)==8, this ensures that the more significant 32 bits of stack_canary are random, too. stack_canary is defined as unsigned long, all the architectures with stack protector support already pick the stack_canary of init as a random unsigned long, and get_random_long() should be as fast as get_random_int(), so there seems to be no good reason against this. This should help if someone tries to guess a stack canary with brute force. (This change has been made in PaX already, with a different RNG.) Signed-off-by: Jann Horn --- kernel/fork.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/kernel/fork.c b/kernel/fork.c index 623259fc794d..d577e2c5d14f 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -518,7 +518,7 @@ static struct task_struct *dup_task_struct(struct task_struct *orig, int node) set_task_stack_end_magic(tsk); #ifdef CONFIG_CC_STACKPROTECTOR - tsk->stack_canary = get_random_int(); + tsk->stack_canary = get_random_long(); #endif /* -- 2.1.4