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Message-Id: <1477922641-2221-1-git-send-email-jann@thejh.net>
Date: Mon, 31 Oct 2016 15:04:01 +0100
From: Jann Horn <jann@...jh.net>
To: Andrew Morton <akpm@...ux-foundation.org>,
Michal Hocko <mhocko@...e.com>,
Ingo Molnar <mingo@...nel.org>,
Andy Lutomirski <luto@...nel.org>,
Kees Cook <keescook@...omium.org>
Cc: linux-kernel@...r.kernel.org,
kernel-hardening@...ts.openwall.com,
Daniel Micay <danielmicay@...il.com>
Subject: [PATCH] fork: make whole stack_canary random
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 <jann@...jh.net>
---
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
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