Re: [PATCH] mm: usercopy: move the virt_addr_valid() below the is_vmalloc_addr()

[Kees Cook]

On Mon, May 09, 2022 at 08:37:32PM -0700, Andrew Morton wrote:
> Matthew & Kees,
> 
> On Thu, 5 May 2022 07:10:37 +0000 Yuanzheng Song <songyuanzheng@xxxxxxxxxx> wrote:
> 
> > The is_kmap_addr() and the is_vmalloc_addr() in the check_heap_object()
> > will not work, because the virt_addr_valid() will exclude the kmap and
> > vmalloc regions. So let's move the virt_addr_valid() below
> > the is_vmalloc_addr().
> 
> The author,
> 
> > Signed-off-by: Yuanzheng Song <songyuanzheng@xxxxxxxxxx>
> 
> Tells me off-list that this fix:
> 
> > --- a/mm/usercopy.c
> > +++ b/mm/usercopy.c
> > @@ -163,9 +163,6 @@ static inline void check_heap_object(const void *ptr, unsigned long n,
> >  {
> >  	struct folio *folio;
> >  
> > -	if (!virt_addr_valid(ptr))
> > -		return;
> > -
> >  	if (is_kmap_addr(ptr)) {
> >  		unsigned long page_end = (unsigned long)ptr | (PAGE_SIZE - 1);
> >  
> > @@ -190,6 +187,9 @@ static inline void check_heap_object(const void *ptr, unsigned long n,
> >  		return;
> >  	}
> >  
> > +	if (!virt_addr_valid(ptr))
> > +		return;
> > +
> >  	folio = virt_to_folio(ptr);
> >  
> >  	if (folio_test_slab(folio)) {
> 
> is required to fix patches "mm/usercopy: Check kmap addresses properly"
> and "mm/usercopy: Detect vmalloc overruns".

Ah, this very well may be true! I will need to study this (or more
likely, I will build some selftests), but I suspect willy knows off the
top of his head. :)

-- 
Kees Cook