Date: Fri, 10 Sep 2010 18:43:57 +0900 (JST) From: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com> To: Roland McGrath <roland@...hat.com> Cc: 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, pageexec@...email.hu, Eugene Teo <eugene@...hat.com> Subject: Re: [PATCH 1/3] setup_arg_pages: diagnose excessive argument size > > 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'm sorry you think it's "very crazy" to implement the required > functionality in the only way available. POSIX requires that execve > fail with E2BIG when the ARG_MAX limit is exceeded. sysconf has to > return the correct actual limit that execve will enforce so that a > conforming application knows how much it can safely attempt to use. > Since the kernel uses the hard-coded RLIMIT_STACK/4 heuristic and does > not expose the true manifest limit any other way, sysconf has to > parallel the kernel's calculation. Hmm... Probably my poor english leaded to misunderstood. I didn't intent glibc is very crazy. I only intended to "even if userland is crazy, I disagree to break userland". And yes, we obviously need to expose ARG_MAX limit to libc. a duplicated heuristic code easily makes confusion and mistake. nobody want such fragile state. however, it's a bit offtopic. anyway. Thanks.
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