Re: [RFC/PATCH] RLIMIT_ARG_MAX

["Carlos O'Donell" <carlos@codesourcery.com>]

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