Re: [patch] net_sched: stack info leak in cbq_dump_wrr()

walter harms
2013-07-30T10:18:03Z

Am 30.07.2013 09:18, schrieb David Miller:
> From: Joe Perches <joe@perches.com>
> Date: Tue, 30 Jul 2013 00:12:32 -0700
>
>> On Tue, 2013-07-30 at 09:55 +0300, Dan Carpenter wrote:
>>> On Mon, Jul 29, 2013 at 01:12:31PM -0700, Joe Perches wrote:
>>>> On Mon, 2013-07-29 at 23:01 +0300, Dan Carpenter wrote:
>>>>> On Mon, Jul 29, 2013 at 12:44:32PM -0700, Joe Perches wrote:
>>>>>> On Mon, 2013-07-29 at 22:36 +0300, Dan Carpenter wrote:
>>>>>>> opt.__reserved isn't cleared so we leak a byte of stack information.
>>>>>> []
>>>>>>> diff --git a/net/sched/sch_cbq.c b/net/sched/sch_cbq.c
>>>>>> []
>>>>>>> @@ -1469,6 +1469,7 @@ static int cbq_dump_wrr(struct sk_buff *skb, struct cbq_class *cl)
>>>>>>> opt.allot = cl->allot;
>>>>>>> opt.priority = cl->priority + 1;
>>>>>>> opt.cpriority = cl->cpriority + 1;
>>>>>>> + opt.__reserved = 0;
>>>>>>> opt.weight = cl->weight;
>>>>>>> if (nla_put(skb, TCA_CBQ_WRROPT, sizeof(opt), &opt))
>>>>>>> goto nla_put_failure;
>>>>>>
>>>>>> Alignment isn't guaranteed here so it'd
>>>>>> probably be better with a memset.
>>>>>>
>>>>>
>>>>> Hm... Which arches would align it differently?
>>>>
>>>> Hey Dan.
>>>>
>>>> None so far as I know, but what difference does it make
>>>> when it's a general correctness issue?
>>>>
>>>
>>> Because I would assume if these aren't aligned the same way we have
>>> far more serious problems than just this one case. It would change
>>> the user space API and break network protocols.
>>
>> <shrug>
>>
>> I didn't say it was necessary to be done here, I said it
>> was a correctness issue. I still believe that's true.
>>
>> The nla_put here is by structure, the struct is unpacked,
>> and it's local to the arch, not a particular endian type.
>>
>> btw: to answer David's question, gcc 4.7 is smart enough
>> to elide resetting values when the struct is initialized
>> to 0 either with a memset or using {0}.
>
> Ok, I've just commited the following, thanks everyone.
>
> --------------------
>>From a0db856a95a29efb1c23db55c02d9f0ff4f0db48 Mon Sep 17 00:00:00 2001
> From: "David S. Miller" <davem@davemloft.net>
> Date: Tue, 30 Jul 2013 00:16:21 -0700
> Subject: [PATCH] net_sched: Fix stack info leak in cbq_dump_wrr().
>
> Make sure the reserved fields, and padding (if any), are
> fully initialized.
>
> Based upon a patch by Dan Carpenter and feedback from
> Joe Perches.
>
> Signed-off-by: David S. Miller <davem@davemloft.net>
> ---
> net/sched/sch_cbq.c | 1 +
> 1 file changed, 1 insertion(+)
>
> diff --git a/net/sched/sch_cbq.c b/net/sched/sch_cbq.c
> index 71a5688..7a42c81 100644
> --- a/net/sched/sch_cbq.c
> +++ b/net/sched/sch_cbq.c
> @@ -1465,6 +1465,7 @@ static int cbq_dump_wrr(struct sk_buff *skb, struct cbq_class *cl)
> unsigned char *b = skb_tail_pointer(skb);
> struct tc_cbq_wrropt opt;
>
> + memset(&opt, 0, sizeof(opt));
> opt.flags = 0;
> opt.allot = cl->allot;
> opt.priority = cl->priority + 1;

You can remove opt.flags = 0; then :=)

re,
wh