[PATCH] fork: make whole stack_canary random

Jann Horn
2016-10-31T14:04:17Z

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@thejh.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