Re: [patch 0/3] no MAX_ARG_PAGES -v2

On Thu, 2007-06-14 at 13:58 -0700, Ollie Wild wrote:

>   A good heuristic, though, might be to limit
> argument size to a percentage (say 25%) of maximum stack size and
> validate this inside copy_strings().

This seems to do:


Signed-off-by: Peter Zijlstra <[email protected]>
---
 fs/exec.c |   17 +++++++++++++++++
 1 file changed, 17 insertions(+)

Index: linux-2.6-2/fs/exec.c
===================================================================
--- linux-2.6-2.orig/fs/exec.c	2007-06-15 11:05:09.000000000 +0200
+++ linux-2.6-2/fs/exec.c	2007-06-15 11:05:18.000000000 +0200
@@ -199,6 +199,23 @@ static struct page *get_arg_page(struct 
 	if (ret <= 0)
 		return NULL;
 
+	if (write) {
+		struct rlimit *rlim = current->signal->rlim;
+		unsigned long size = bprm->vma->vm_end - bprm->vma->vm_start;
+
+		/*
+		 * Limit to 1/4-th the stack size for the argv+env strings.
+		 * This ensures that:
+		 *  - the remaining binfmt code will not run out of stack space,
+		 *  - the program will have a reasonable amount of stack left
+		 *    to work from.
+		 */
+		if (size > rlim[RLIMIT_STACK].rlim_cur / 4) {
+			put_page(page);
+			return NULL;
+		}
+	}
+
 	return page;
 }