netdev - Re: [PATCH net-next-2.6] net_sched: sch

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Date:	Thu, 27 Jan 2011 14:54:42 +0800
From:	Changli Gao <xiaosuo@...il.com>
To:	Joe Perches <joe@...ches.com>
Cc:	David Miller <davem@...emloft.net>, eric.dumazet@...il.com,
	netdev@...r.kernel.org, john.r.fastabend@...el.com
Subject: Re: [PATCH net-next-2.6] net_sched: sch_mqprio: dont leak kernel memory

On Thu, Jan 27, 2011 at 2:04 PM, Joe Perches <joe@...ches.com> wrote:
> On Wed, 2011-01-26 at 11:55 -0800, David Miller wrote:
>> From: Joe Perches <joe@...ches.com>
>> Date: Wed, 26 Jan 2011 09:43:43 -0800
>> > On Wed, 2011-01-26 at 18:21 +0100, Eric Dumazet wrote:
>> >> mqprio_dump() should make sure all fields of struct tc_mqprio_qopt are
>> >> initialized.
>> >> Signed-off-by: Eric Dumazet <eric.dumazet@...il.com>
>> >> CC: John Fastabend <john.r.fastabend@...el.com>
>> >> ---
>> >>  net/sched/sch_mqprio.c |    2 +-
>> >>  1 file changed, 1 insertion(+), 1 deletion(-)
>> >>
>> >> diff --git a/net/sched/sch_mqprio.c b/net/sched/sch_mqprio.c
>> >> index fbc6f53..effd4ee 100644
>> >> --- a/net/sched/sch_mqprio.c
>> >> +++ b/net/sched/sch_mqprio.c
>> >> @@ -215,7 +215,7 @@ static int mqprio_dump(struct Qdisc *sch, struct sk_buff *skb)
>> >>    struct net_device *dev = qdisc_dev(sch);
>> >>    struct mqprio_sched *priv = qdisc_priv(sch);
>> >>    unsigned char *b = skb_tail_pointer(skb);
>> >> -  struct tc_mqprio_qopt opt;
>> >> +  struct tc_mqprio_qopt opt = { 0 };
>> > I think the best style to use memset so that any
>> > possible struct padding is guaranteed to be zeroed.
>> Such padding does not exist, and we won't add such padding since this is
>> a user visible data structure and thus whose layout is cast in stone.
>
> /* MQPRIO */
> #define TC_QOPT_BITMASK 15
> #define TC_QOPT_MAX_QUEUE 16
>
> struct tc_mqprio_qopt {
> __u8 num_tc; // 1
> __u8 prio_tc_map[TC_QOPT_BITMASK + 1]; // 16
> __u8 hw; // 1
> __u16 count[TC_QOPT_MAX_QUEUE]; // 32
> __u16 offset[TC_QOPT_MAX_QUEUE]; //32
> };
>
> I believe this struct needs to be declared __packed.
>
> It could otherwise be 24 bytes not 22.
> Or if char array declarations have a different
> alignment requirement, could be any size.
>

The total size is 1 + 16 + 1 + 32 + 32 = 82.

How do you get 24 or 22?

> memset is better than {0}.
>


-- 
Regards,
Changli Gao(xiaosuo@...il.com)
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