Re: [PATCH V4 1/2] ptr_ring: fail early if queue occupies more than KMALLOC_MAX_SIZE

[Jason Wang]

On 2018å02æ11æ 03:32, Eric Biggers wrote:
> Hi Jason,
>
> On Fri, Feb 09, 2018 at 05:45:49PM +0800, Jason Wang wrote:
> > To avoid slab to warn about exceeded size, fail early if queue
> > occupies more than KMALLOC_MAX_SIZE.
> >
> > Reported-by: syzbot+e4d4f9ddd4295539735d@xxxxxxxxxxxxxxxxxxxxxxxxx
> > Fixes: 2e0ab8ca83c12 ("ptr_ring: array based FIFO for pointers")
> > Signed-off-by: Jason Wang <jasowang@xxxxxxxxxx>
> > ---
> >   include/linux/ptr_ring.h | 2 ++
> >   1 file changed, 2 insertions(+)
> >
> > diff --git a/include/linux/ptr_ring.h b/include/linux/ptr_ring.h
> > index 1883d61..6051a5f 100644
> > --- a/include/linux/ptr_ring.h
> > +++ b/include/linux/ptr_ring.h
> > @@ -466,6 +466,8 @@ static inline int ptr_ring_consume_batched_bh(struct ptr_ring *r,
> >   
> >   static inline void **__ptr_ring_init_queue_alloc(unsigned int size, gfp_t gfp)
> >   {
> > +	if (size * sizeof(void *) > KMALLOC_MAX_SIZE)
> > +		return NULL;
> Are you sure that size can't be over 0x40000000?  The proper way to write this
> (safe from integer overflow) would be:
>
> 	if (size > KMALLOC_MAX_SIZE / sizeof(void *))
> 		return NULL;
>
> - Eric

Good catch.

Will post a fix.

Thanks