linux-kernel - Re: [PATCH] exec: separate MM_ANONPAGES and RLIMIT

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Date:   Mon, 26 Nov 2018 09:34:04 -0800
From:   Guenter Roeck <linux@...ck-us.net>
To:     Oleg Nesterov <oleg@...hat.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Ben Woodard <woodard@...hat.com>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Kees Cook <keescook@...omium.org>,
        Michal Hocko <mhocko@...e.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] exec: separate MM_ANONPAGES and RLIMIT_STACK accounting

Hi Oleg,

On Mon, Nov 26, 2018 at 01:23:07PM +0100, Oleg Nesterov wrote:
> Hi Guenter,
> 
> On 11/23, Guenter Roeck wrote:
> >
> > On Mon, Nov 12, 2018 at 05:09:10PM +0100, Oleg Nesterov wrote:
> > > get_arg_page() checks bprm->rlim_stack.rlim_cur and re-calculates the
> > > "extra" size for argv/envp pointers every time, this is a bit ugly and
> > > even not strictly correct: acct_arg_size() must not account this size.
> > >
> > > Remove all the rlimit code in get_arg_page(). Instead, add bprm->argmin
> > > calculated once at the start of __do_execve_file() and change copy_strings
> > > to check bprm->p >= bprm->argmin.
> > >
> > > The patch adds the new helper, prepare_arg_pages() which initializes
> > > bprm->argc/envc and bprm->argmin.
> > >
> > > Signed-off-by: Oleg Nesterov <oleg@...hat.com>
> > > Acked-by: Kees Cook <keescook@...omium.org>
> >
> > This patch results in various qemu boot failures in -next. Bisect logs
> > are attached. It looks like all nommu boots are failing.
>                                   ^^^^^
> 
> Ah, thanks.
> 
> Yes, I forgot about the !CONFIG_MMU version of get_arg_page() which doesn't
> check RLIMIT_STACK at all.
> 
> I'll send the trivial fix. Meanwile, could you test the patch below? to ensure
> this is the only problem.
> 

Tested-by: Guenter Roeck <linux@...ck-us.net>

with arm:mps2-an385, xtensa:kc705-nommu, and m68k:mcf5208evb.

Thanks,
Guenter

> Oleg.
> 
> --- a/fs/exec.c
> +++ b/fs/exec.c
> @@ -526,8 +526,10 @@ static int copy_strings(int argc, struct user_arg_ptr argv,
>  		pos = bprm->p;
>  		str += len;
>  		bprm->p -= len;
> +#ifdef CONFIG_MMU
>  		if (bprm->p < bprm->argmin)
>  			goto out;
> +#endif
>  
>  		while (len > 0) {
>  			int offset, bytes_to_copy;
>