linux-kernel - Re: [PATCH net] ptr_ring: fail early if queue occupies more than KMALLOC_MAX

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Message-ID: <20180208174301-mutt-send-email-mst@kernel.org>
Date:   Thu, 8 Feb 2018 17:44:48 +0200
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Jason Wang <jasowang@...hat.com>
Cc:     linux-kernel@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH net] ptr_ring: fail early if queue occupies more than
 KMALLOC_MAX_SIZE

On Wed, Feb 07, 2018 at 04:08:25PM +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@...kaller.appspotmail.com
> Signed-off-by: Jason Wang <jasowang@...hat.com>
> ---
>  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..4b862da 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 > KMALLOC_MAX_SIZE)
> +		return NULL;
>  	return kcalloc(size, sizeof(void *), gfp);
>  }

I guess this approach does begin to make more sense
at least as a temporary stop-gap.

But does this actually prevent the crash in all cases?

size is in void* entry units, KMALLOC_MAX_SIZE is in bytes.

>  
> -- 
> 2.7.4