linux-kernel - Re: [PATCH]highmem_32.c: add argument pointer checking

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Date:	Tue, 30 Jun 2009 00:11:03 +0800
From:	"Figo.zhang" <figo1802@...il.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	lkml <linux-kernel@...r.kernel.org>, Andrew Morton <akpm@...l.org>
Subject: Re: [PATCH]highmem_32.c: add argument pointer checking

On Mon, 2009-06-29 at 06:09 +0200, Ingo Molnar wrote:
> * Figo.zhang <figo1802@...il.com> wrote:
> 
> > It had better add argument pointer checking.
> > 
> > If any guys write driver want to alloc hightmem and pass a no-initial pointer,
> > it would be crashed.
> > 
> > Signed-off-by: Figo.zhang <figo1802@...il.com>
> > ---  
> > arch/x86/mm/highmem_32.c |    4 ++++
> >  1 files changed, 4 insertions(+), 0 deletions(-)
> > 
> > diff --git a/arch/x86/mm/highmem_32.c b/arch/x86/mm/highmem_32.c
> > index 58f621e..e52e1a9 100644
> > --- a/arch/x86/mm/highmem_32.c
> > +++ b/arch/x86/mm/highmem_32.c
> > @@ -31,6 +31,7 @@ void *kmap_atomic_prot(struct page *page, enum km_type type, pgprot_t prot)
> >  {
> >  	enum fixed_addresses idx;
> >  	unsigned long vaddr;
> > +	BUG_ON(!page);
> >  
> >  	/* even !CONFIG_PREEMPT needs this, for in_atomic in do_page_fault */
> >  	pagefault_disable();
> > @@ -58,6 +59,9 @@ void kunmap_atomic(void *kvaddr, enum km_type type)
> >  	unsigned long vaddr = (unsigned long) kvaddr & PAGE_MASK;
> >  	enum fixed_addresses idx = type + KM_TYPE_NR*smp_processor_id();
> >  
> > +	if(!kvaddr)
> > +		return;
> > +
> 
> (Please run patches through scripts/checkpatch.pl before 
> submission.)
> 
> Also, what's the improvement here? Before the patch we'd crash on a 
> NULL dereference ... after the patch we'd crash on a BUG_ON().

why it would be crash on BUG_ON()?
I motify it and test on my computer, it would not crash.

Best Regards,
Figo.zhang

> 
> Furthermore, he kunmap_atomic() change is outright wrong - it will 
> now allow NULL kunmaps, which can hide bugs in drivers.
> 
> 	Ingo

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