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

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Date:	Thu, 27 Jan 2011 08:04:03 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Joe Perches <joe@...ches.com>
Cc:	David Miller <davem@...emloft.net>, netdev@...r.kernel.org,
	john.r.fastabend@...el.com
Subject: Re: [PATCH net-next-2.6] net_sched: sch_mqprio: dont leak kernel
 memory

Le mercredi 26 janvier 2011 à 22:04 -0800, Joe Perches a écrit :

> /* MQPRIO */
> #define TC_QOPT_BITMASK 15
> #define TC_QOPT_MAX_QUEUE 16
> 
> struct tc_mqprio_qopt {
> __u8 num_tc;
> __u8 prio_tc_map[TC_QOPT_BITMASK + 1];
> __u8 hw;
> __u16 count[TC_QOPT_MAX_QUEUE];
> __u16 offset[TC_QOPT_MAX_QUEUE];
> };
> 
> I believe this struct needs to be declared __packed.
> 

Oh my god. Yet another ugly thing.

> It could otherwise be 24 bytes not 22.

22 ? You are kidding probably. Its 82 exactly.

Listen, I doubled check my patch, its good, while your rants are lazy.

> Or if char array declarations have a different
> alignment requirement, could be any size.
> 

If if if... could could could...


> memset is better than {0}.
> 

You never stop do you ?

The bigger object is u16, therefore alignof() is 2, not 4

No ABI requires a short (u16) is aligned on 4 byte boundary.

If you find a compiler not respecting this, you can bet linux wont run
at all if compiled with it. mqprio 'potential 2 bytes leak' will hardly
be a problem.



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