Re: [PATCH net V3 2/2] ptr_ring: fail on large queue size (>64K)

From: David Miller <davem@davemloft.net>
To: jasowang@redhat.com
Cc: mst@redhat.com, netdev@vger.kernel.org
Subject: Re: [PATCH net V3 2/2] ptr_ring: fail on large queue size (>64K)
Date: Thu, 08 Feb 2018 14:09:59 -0500 (EST)	[thread overview]
Message-ID: <20180208.140959.1771270473230462281.davem@davemloft.net> (raw)
In-Reply-To: <1518062365-8596-2-git-send-email-jasowang@redhat.com>

From: Jason Wang <jasowang@redhat.com>
Date: Thu,  8 Feb 2018 11:59:25 +0800

> We need limit the maximum size of queue, otherwise it may cause
> several side effects e.g slab will warn when the size exceeds
> KMALLOC_MAX_SIZE. Using KMALLOC_MAX_SIZE still looks too so this patch
> tries to limit it to 64K. This value could be revisited if we found a
> real case that needs more.
> 
> Reported-by: syzbot+e4d4f9ddd4295539735d@syzkaller.appspotmail.com
> Fixes: 2e0ab8ca83c12 ("ptr_ring: array based FIFO for pointers")
> Signed-off-by: Jason Wang <jasowang@redhat.com>
 ...
> @@ -466,6 +468,8 @@ 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 > PTR_RING_MAX_ALLOC)
> +		return NULL;
>  	return kvmalloc_array(size, sizeof(void *), gfp | __GFP_ZERO);
>  }

This doesn't limit the allocation to 64K.  It limits it to 64K * sizeof(void *).