Re: [RFC/PATCH] RLIMIT_ARG_MAX

Carlos O'Donell
2008-03-01T14:26:35Z

Linus Torvalds wrote:
> 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?

This is perfect. As the original submitter of the bug my primary
interest is in having the regression fixed.

> 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;

Could you use ARG_MAX as defined in include/linux/limits.h?

>
> /*
> * 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;

Cheers,
Carlos.
--
Carlos O'Donell
CodeSourcery
carlos@codesourcery.com
(650) 331-3385 x716