linux-kernel - Re: [kernel-hardening] [PATCH 4.4 47/90] stackprotector: Increase the per-task stack canarys random range from 32 bits to 64 bits on 64-bit platforms

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Date:   Mon, 12 Jun 2017 17:45:54 +0200
From:   Jann Horn <jannh@...gle.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     kernel list <linux-kernel@...r.kernel.org>, stable@...r.kernel.org,
        Daniel Micay <danielmicay@...il.com>,
        Arjan van de Ven <arjan@...ux.intel.com>,
        Rik van Riel <riel@...hat.com>,
        Kees Cook <keescook@...omium.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Kernel Hardening <kernel-hardening@...ts.openwall.com>,
        Ingo Molnar <mingo@...nel.org>
Subject: Re: [kernel-hardening] [PATCH 4.4 47/90] stackprotector: Increase the
 per-task stack canarys random range from 32 bits to 64 bits on 64-bit platforms

Ah, nevermind, I just saw that this was changed in
https://git.kernel.org/pub/scm/linux/kernel/git/stable/stable-queue.git/tree/queue-4.4/drivers-char-random-add-get_random_long.patch
.

On Mon, Jun 12, 2017 at 5:41 PM, Jann Horn <jannh@...gle.com> wrote:
> AFAICS get_random_long() doesn't exist in 4.4 (except in
> arch/x86/boot/compressed/aslr.c)? IIRC the same problem already
> occured with another kernel version?
>
> On Mon, Jun 12, 2017 at 5:25 PM, Greg Kroah-Hartman
> <gregkh@...uxfoundation.org> wrote:
>> 4.4-stable review patch.  If anyone has any objections, please let me know.
>>
>> ------------------
>>
>> From: Daniel Micay <danielmicay@...il.com>
>>
>> commit 5ea30e4e58040cfd6434c2f33dc3ea76e2c15b05 upstream.
>>
>> The stack canary is an 'unsigned long' and should be fully initialized to
>> random data rather than only 32 bits of random data.
>>
>> Signed-off-by: Daniel Micay <danielmicay@...il.com>
>> Acked-by: Arjan van de Ven <arjan@...ux.intel.com>
>> Acked-by: Rik van Riel <riel@...hat.com>
>> Acked-by: Kees Cook <keescook@...omium.org>
>> Cc: Arjan van Ven <arjan@...ux.intel.com>
>> Cc: Linus Torvalds <torvalds@...ux-foundation.org>
>> Cc: Peter Zijlstra <peterz@...radead.org>
>> Cc: Thomas Gleixner <tglx@...utronix.de>
>> Cc: kernel-hardening@...ts.openwall.com
>> Cc: stable@...r.kernel.org
>> Link: http://lkml.kernel.org/r/20170504133209.3053-1-danielmicay@gmail.com
>> Signed-off-by: Ingo Molnar <mingo@...nel.org>
>> Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
>>
>> ---
>>  kernel/fork.c |    2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> --- a/kernel/fork.c
>> +++ b/kernel/fork.c
>> @@ -368,7 +368,7 @@ static struct task_struct *dup_task_stru
>>         set_task_stack_end_magic(tsk);
>>
>>  #ifdef CONFIG_CC_STACKPROTECTOR
>> -       tsk->stack_canary = get_random_int();
>> +       tsk->stack_canary = get_random_long();
>>  #endif
>>
>>         /*
>>
>>