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SubjectRe: [PATCH]highmem_32.c: add argument pointer checking
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On Mon, 2009-06-29 at 06:09 +0200, Ingo Molnar wrote:
> * Figo.zhang <figo1802@gmail.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@gmail.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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