linux-kernel - Re: [patch 3/3] mm: variable length argument support

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Message-Id: <1186514797.11797.173.camel@lappy>
Date:	Tue, 07 Aug 2007 21:26:36 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Olaf Hering <olaf@...fle.de>, linux-kernel@...r.kernel.org,
	parisc-linux@...ts.parisc-linux.org, linux-mm@...ck.org,
	linux-arch@...r.kernel.org, Ollie Wild <aaw@...gle.com>,
	Ingo Molnar <mingo@...e.hu>, Andi Kleen <ak@...e.de>
Subject: Re: [patch 3/3] mm: variable length argument support

On Tue, 2007-08-07 at 12:20 -0700, Andrew Morton wrote:
> On Tue, 7 Aug 2007 21:03:57 +0200
> Olaf Hering <olaf@...fle.de> wrote:
> 
> > On Wed, Jun 13, Peter Zijlstra wrote:
> > 
> > > From: Ollie Wild <aaw@...gle.com>
> > > 
> > > Remove the arg+env limit of MAX_ARG_PAGES by copying the strings directly
> > > from the old mm into the new mm.
> > 
> > > +++ linux-2.6-2/include/linux/binfmts.h	2007-06-13 11:52:46.000000000 +0200
> > > @@ -6,11 +6,13 @@
> > >  struct pt_regs;
> > >  
> > >  /*
> > > - * MAX_ARG_PAGES defines the number of pages allocated for arguments
> > > - * and envelope for the new program. 32 should suffice, this gives
> > > - * a maximum env+arg of 128kB w/4KB pages!
> > > + * These are the maximum length and maximum number of strings passed to the
> > > + * execve() system call.  MAX_ARG_STRLEN is essentially random but serves to
> > > + * prevent the kernel from being unduly impacted by misaddressed pointers.
> > > + * MAX_ARG_STRINGS is chosen to fit in a signed 32-bit integer.
> > >   */
> > > -#define MAX_ARG_PAGES 32
> > > +#define MAX_ARG_STRLEN (PAGE_SIZE * 32)
> > > +#define MAX_ARG_STRINGS 0x7FFFFFFF
> > 
> > This adds a new usage of PAGE_SIZE to an exported header.
> > How can this be fixed for 2.6.23?
> 
> Put #ifdef __KERNEL__ around it?

Sounds like a good idea, since its new there should not yet be anybody
using it.

If anything, someone used to use MAX_ARG_PAGES in userspace, which we
just now broke. Olaf said he'd grep a distro source base to find out :-)

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