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

Peter Zijlstra
2007-06-15T09:24:52Z

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 <a.p.zijlstra@chello.nl>
---
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;
}