Commit a64e715f authored Mar 03, 2008 by Linus Torvalds

Allow ARG_MAX execve string space even with a small stack limit



The new code that removed the limitation on the execve string size
(which was historically 32 pages) replaced it with a much softer limit
based on RLIMIT_STACK which is usually much larger than the traditional
limit.  See commit b6a2fea3 ("mm:
variable length argument support") for details.

However, if you have a small stack limit (perhaps because you need lots
of stacks in a threaded environment), the new heuristic of allowing up
to 1/4th of RLIMIT_STACK to be used for argument and environment strings
could actually be smaller than the old limit.

So just say that it's ok to have up to ARG_MAX strings regardless of the
value of RLIMIT_STACK, and check the rlimit only when going over that
traditional limit.

(Of course, if you actually have a *really* small stack limit, the whole
stack itself will be limited before you hit ARG_MAX, but that has always
been true and is clearly the right behaviour anyway).

Acked-by: Carlos O'Donell <carlos@codesourcery.com>
Cc: Michael Kerrisk <michael.kerrisk@googlemail.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Ollie Wild <aaw@google.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent a345b4ba

fs/exec.c

+9 −1

Original line number	Diff line number	Diff line
		@@ -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 (ARG_MAX)
		* of argument strings even with small stacks
		*/
		if (size <= ARG_MAX)
		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;