linux-kernel - Re: [RFC/PATCH] RLIMIT_ARG

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Date:	Fri, 29 Feb 2008 13:57:48 -0800 (PST)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Michael Kerrisk <michael.kerrisk@...glemail.com>
cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>, aaw <aaw@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	carlos@...esourcery.com, Alan Cox <alan@...rguk.ukuu.org.uk>,
	linux-kernel <linux-kernel@...r.kernel.org>, drepper@...hat.com,
	mtk.manpages@...il.com, Geoff Clare <gwc@...ngroup.org>
Subject: Re: [RFC/PATCH] RLIMIT_ARG_MAX



On Fri, 29 Feb 2008, Linus Torvalds wrote:
> 
> I do agree that we should at least make the "MAX(stacksize/4, 128k)" 
> change for backwards compatibility.

How about something like this?

The alternative is to just remove that size check entirely, and depend on 
get_user_pages() doing the stack limit check (among all the *other* checks 
it does when it does the acct_stack_growth() thing).

I'd almost prefer that simpler approach, but I don't have any really 
strong preferences. Anybody?

		Linus

---
 fs/exec.c |   10 +++++++++-
 1 files changed, 9 insertions(+), 1 deletions(-)

diff --git a/fs/exec.c b/fs/exec.c
index a44b142..e91f9cb 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -173,8 +173,15 @@ static struct page *get_arg_page(struct linux_binprm *bprm, unsigned long pos,
 		return NULL;
 
 	if (write) {
-		struct rlimit *rlim = current->signal->rlim;
 		unsigned long size = bprm->vma->vm_end - bprm->vma->vm_start;
+		struct rlimit *rlim;
+
+		/*
+		 * We've historically supported up to 32 pages of argument
+		 * strings even with small stacks
+		 */
+		if (size <= 32*PAGE_SIZE)
+			return page;
 
 		/*
 		 * Limit to 1/4-th the stack size for the argv+env strings.
@@ -183,6 +190,7 @@ static struct page *get_arg_page(struct linux_binprm *bprm, unsigned long pos,
 		 *  - the program will have a reasonable amount of stack left
 		 *    to work from.
 		 */
+		rlim = current->signal->rlim;
 		if (size > rlim[RLIMIT_STACK].rlim_cur / 4) {
 			put_page(page);
 			return NULL;
--
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