Re: [RFC/PATCH] RLIMIT_ARG_MAX

[Linus Torvalds <torvalds@linux-foundation.org>]

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;