Re: [RFC/PATCH] RLIMIT_ARG_MAX

Linus Torvalds
2008-02-29T21:59:17Z

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;