Date: Wed, 15 Sep 2010 00:27:58 +0200 From: pageexec@...email.hu To: Roland McGrath <roland@...hat.com> CC: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>, Brad Spengler <spender@...ecurity.net>, Linus Torvalds <torvalds@...ux-foundation.org>, Andrew Morton <akpm@...ux-foundation.org>, linux-kernel@...r.kernel.org, oss-security@...ts.openwall.com, Solar Designer <solar@...nwall.com>, Kees Cook <kees.cook@...onical.com>, Al Viro <viro@...iv.linux.org.uk>, Oleg Nesterov <oleg@...hat.com>, Neil Horman <nhorman@...driver.com>, linux-fsdevel@...r.kernel.org, Eugene Teo <eugene@...hat.com> Subject: Re: [PATCH 1/3] setup_arg_pages: diagnose excessive argument size On 14 Sep 2010 at 14:16, Roland McGrath wrote: > > obviously an AT_ARGMAX computed at execve time would be based on the rlimits > > as well and if later userland changed the rlimits, it'd be userland's problem, > > not that of the kernel (or the kernel could refuse a change that would violate > > its earlier promise). > > This would thoroughly defeat the purpose of adding the thing. The > only reason to have a new thing is so that userland does not have to > mirror the kernel's policy (as it attempts to do now, with the 1/4 > calculation). If the new thing is not something that userland can > use consistently so as not to have to know what the kernel's actual > policy is, then I don't see the point of it at all. userland could never rely on the kernel's policy at all since get_arg_page could have failed for more reasons than overstepping the currently hardcoded ARG_MAX check in there. so what AT_ARGMAX would buy us is to allow the kernel policy to change over time, but it's never been about guarantees, whether POSIX wants such a thing or not. > > > auxv is only appropriate for things that > > > are known at the time of the exec and won't change thereafter. > > > > you mean stuff like AT_EUID et al.? ;) > > The information that these give is about the conditions at startup. > That's what they mean to userland, and userland only uses them to know > the situation before it has made any calls. The definition of AT_EUID > is "effective user ID at program startup", and that fact does not > change. just for my own curiosity, where does this definition come from?
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