From a64e715fc74b1a7dcc5944f848acc38b2c4d4ee2 Mon Sep 17 00:00:00 2001 From: Linus Torvalds Date: Mon, 3 Mar 2008 10:12:14 -0800 Subject: [PATCH] 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 b6a2fea39318e43fee84fa7b0b90d68bed92d2ba ("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 Cc: Michael Kerrisk Cc: Peter Zijlstra Cc: Ollie Wild Signed-off-by: Linus Torvalds --- fs/exec.c | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-) diff --git a/fs/exec.c b/fs/exec.c index a44b142..54a0a55 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 (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; -- 2.7.4