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Subject: Re: [PATCH] net: sched: Fix memory exposure from short TCA_U32_SEL
To:     Al Viro <viro@ZenIV.linux.org.uk>,
        Kees Cook <keescook@chromium.org>
Cc:     LKML <linux-kernel@vger.kernel.org>,
        Cong Wang <xiyou.wangcong@gmail.com>,
        Jiri Pirko <jiri@resnulli.us>,
        "David S. Miller" <davem@davemloft.net>,
        Network Development <netdev@vger.kernel.org>
References: <20180826055801.GA42063@beast>
 <20180826061534.GT6515@ZenIV.linux.org.uk>
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 <20180826173236.GU6515@ZenIV.linux.org.uk>
 <20180826225749.GY6515@ZenIV.linux.org.uk>
From:   Jamal Hadi Salim <jhs@mojatatu.com>
Message-ID: <cb9d4e74-3498-48bd-45e0-05e925dbdb5b@mojatatu.com>
Date:   Mon, 27 Aug 2018 07:57:58 -0400
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On 2018-08-26 6:57 p.m., Al Viro wrote:
> On Sun, Aug 26, 2018 at 06:32:37PM +0100, Al Viro wrote:
> 
>> As far as I can tell, the solution is
> [snip long and painful reasoning]
>> pointers, and not in provably opaque fashion.  Theoretically, the three tcf_...
>> inlines above need another look; fortunately, they don't use ->next at all, not to
>> mention not being used anywhere outside of net/sched/*.c
>>
>> 	The 80 lines above prove that we only need to grep net/sched/*.c for
>> tcf_proto_ops method calls.  And only because we don't have (thank $DEITY)
>> anything that could deconstruct types - as soon as some bastard grows means
>> to say "type of the second argument of the function pointed to by p", this
>> kind of analysis, painful as it is, goes out of window.  Even as it is,
>> do you really like the idea of newbies trying to get through the exercises
>> like the one above?
> 
> BTW, would there be any problem if we took the definitions of tcf_proto and
> tcf_proto_ops to e.g. net/sched/tcf_proto.h (along with the three inlines in
> in pkt_cls.h), left forwards in sch_generic.h and added includes of "tcf_proto.h"
> where needed in net/sched/*.c?
> 

I cant think of any challenges. Cong/Jiri? Would it require development
time classifiers/actions/qdiscs to sit in that directory (I suspect you
dont want them in include/net).
BTW, the idea of improving grep-ability of the code by prefixing the
ops appropriately makes sense. i.e we should have ops->cls_init,
ops->act_init etc.

cheers,
jamal

> That would make tcf_proto/tcf_proto_ops opaque outside of net/sched, reducing
> the exposure of internals.  Something like a diff below (against net/master,
> builds clean, ought to result in identical binary):
>