Re: [NETFILTER]: Move extensions' arguments into compound structure (1/2)

[Patrick McHardy <kaber@trash.net>]

Jan Engelhardt wrote:
> On Sunday 2008-10-05 12:26, Patrick McHardy wrote:
>>>
>>> Constructing the xt_match_param for example in ipt_do_table() instead
>>> of do_match() would mean that iff some extension trashed, say,
>>> par->in, then all future extensions would get that new value, which
>>> is of course not what we wanted.
>> It isn't what we want? Why does it change the global value then?
> 
> For example, ebt_snat does this:
> 
> bool ebt_snat_tg_check(table, e, target, data, hookmask)
> {
> 	if (hookmask & base_chain_bit && tmp == EBT_RETURN)
> 		return false;
> 	hookmask &= ~base_chain_bit;
> 	if (hookmask & yada)
> 		whatever;
> 	else
> 		foo;
> }
> 
> hookmask was coiped to the function by use of the stack (the usual stuff),
> but with the argument consolidation, it now reads like:
> 
> 	par->hookmask &= ~base_chain_bit;
> 
> which means that the caller will see the altered hook mask. This is why
> the struct is thrown away everytime.

OK, so ebt_snat_tg_check has to use a local copy.

>>> Requesting verdict from you. :)
>>> Make it const so that extensions don't tamper with it?
>> Preferrably, yes.
>>
> Perfect.

Great.