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

[Peter Zijlstra]

On Wed, 2007-08-22 at 11:48 +0300, Dan Aloni wrote:
> On Wed, Jun 13, 2007 at 12:03:37PM +0200, Peter Zijlstra wrote:
> > From: Ollie Wild <aaw@xxxxxxxxxx>
> > 
> > Remove the arg+env limit of MAX_ARG_PAGES by copying the strings directly
> > from the old mm into the new mm.
> > 
> [...]
> > +static int __bprm_mm_init(struct linux_binprm *bprm)
> > +{
> [...]
> > +	vma->vm_flags = VM_STACK_FLAGS;
> > +	vma->vm_page_prot = protection_map[vma->vm_flags & 0x7];
> > +	err = insert_vm_struct(mm, vma);
> > +	if (err) {
> > +		up_write(&mm->mmap_sem);
> > +		goto err;
> > +	}
> > +
> 
> That change causes a crash in khelper when overcommit_memory = 2 
> under 2.6.23-rc3.
> 
> When a khelper execs, at __bprm_mm_init() current->mm is still NULL.
> insert_vm_struct() calls security_vm_enough_memory(), which calls 
> __vm_enough_memory(), and that's where current->mm->total_vm gets 
> dereferenced.

Alan proposed this patch:

http://lkml.org/lkml/2007/8/13/782

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