Re: [PATCH 1/3] setup_arg_pages: diagnose excessive argument size

[KOSAKI Motohiro <kosaki.motohiro () jp fujitsu com>]

> I still don't think this addresses the whole problem.  Without question,
> the rlimit / 4 check is bogus.  If nobody agrees with the intent of that 
> check, then it should be removed, but I think the better solution is to 
> fix the check so that it matches its original intent: let the initial 
> stack setup be up to 1/Xth of the min(rlimit, TASK_SIZE dependent upon 
> personality), which allows space for additional stack setup in the ELF 
> loader and then further growth once the process is live.  If that 
> amount is overstepped, then the exec will return an error to the calling 
> process instead of being terminated.
>
> It might be useful to consult with the people who introduced/approved 
> the check in the first place, as they seemed to have reasons for 
> implementing it.

Brad, sorry, I have bad news. glibc sysconf(_SC_ARG_MAX) is implemented
by hard coded RLIMIT_STACK/4 heuristics. That said, at least _now_, we
can't change this even though you disliked. That said, we can't break
userland even though userland library is very crazy.

I don't dislike your "1/Xth of the min(rlimit, TASK_SIZE dependent upon 
> personality)" idea. however I think You and Roland haven't agreed this
point yet. he seems to want "unlimited" works as "unlimited". then, now
I don't make such patch. Instead, I would propose to insert 
__vm_enough_memory() check in execve() pass. It prevent almost argv attack.