Re: [PATCH net-next] virtio-net: fix use-after-free in skb_gro_receive

[Jason Wang <jasowang@redhat.com>]

在 2021/4/23 下午12:19, Xuan Zhuo 写道:
> On Fri, 23 Apr 2021 12:08:34 +0800, Jason Wang <jasowang@redhat.com> wrote:
>> 在 2021/4/22 下午11:16, Xuan Zhuo 写道:
>>> When "headroom" > 0, the actual allocated memory space is the entire
>>> page, so the address of the page should be used when passing it to
>>> build_skb().
>>>
>>> BUG: KASAN: use-after-free in skb_gro_receive (net/core/skbuff.c:4260)
>>> Write of size 16 at addr ffff88811619fffc by task kworker/u9:0/534
>>> CPU: 2 PID: 534 Comm: kworker/u9:0 Not tainted 5.12.0-rc7-custom-16372-gb150be05b806 #3382
>>> Hardware name: QEMU MSN2700, BIOS rel-1.13.0-0-gf21b5a4aeb02-prebuilt.qemu.org 04/01/2014
>>> Workqueue: xprtiod xs_stream_data_receive_workfn [sunrpc]
>>> Call Trace:
>>>    <IRQ>
>>> dump_stack (lib/dump_stack.c:122)
>>> print_address_description.constprop.0 (mm/kasan/report.c:233)
>>> kasan_report.cold (mm/kasan/report.c:400 mm/kasan/report.c:416)
>>> skb_gro_receive (net/core/skbuff.c:4260)
>>> tcp_gro_receive (net/ipv4/tcp_offload.c:266 (discriminator 1))
>>> tcp4_gro_receive (net/ipv4/tcp_offload.c:316)
>>> inet_gro_receive (net/ipv4/af_inet.c:1545 (discriminator 2))
>>> dev_gro_receive (net/core/dev.c:6075)
>>> napi_gro_receive (net/core/dev.c:6168 net/core/dev.c:6198)
>>> receive_buf (drivers/net/virtio_net.c:1151) virtio_net
>>> virtnet_poll (drivers/net/virtio_net.c:1415 drivers/net/virtio_net.c:1519) virtio_net
>>> __napi_poll (net/core/dev.c:6964)
>>> net_rx_action (net/core/dev.c:7033 net/core/dev.c:7118)
>>> __do_softirq (./arch/x86/include/asm/jump_label.h:25 ./include/linux/jump_label.h:200 ./include/trace/events/irq.h:142 kernel/softirq.c:346)
>>> irq_exit_rcu (kernel/softirq.c:221 kernel/softirq.c:422 kernel/softirq.c:434)
>>> common_interrupt (arch/x86/kernel/irq.c:240 (discriminator 14))
>>> </IRQ>
>>>
>>> Fixes: fb32856b16ad ("virtio-net: page_to_skb() use build_skb when there's sufficient tailroom")
>>> Signed-off-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
>>> Reported-by: Ido Schimmel <idosch@nvidia.com>
>>> Tested-by: Ido Schimmel <idosch@nvidia.com>
>>> ---
>>
>> Acked-by: Jason Wang <jasowang@redhat.com>
>>
>> The codes became hard to read, I think we can try to do some cleanups on
>> top to make it easier to read.
>>
>> Thanks
> Yes, this piece of code needs to be sorted out. Especially the big and mergeable
> scenarios should be handled separately. Remove the mergeable code from this
> function, and mergeable uses a new function alone.


Right, another thing is that we may consider to relax the checking of 
len < GOOD_COPY_LEN.

Our QE still see low PPS compared with the code before 3226b158e67c 
("net: avoid 32 x truesize under-estimation for tiny skbs").

Thanks


>
> Thanks.
>
>>
>>>    drivers/net/virtio_net.c | 12 +++++++++---
>>>    1 file changed, 9 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
>>> index 74d2d49264f3..7fda2ae4c40f 100644
>>> --- a/drivers/net/virtio_net.c
>>> +++ b/drivers/net/virtio_net.c
>>> @@ -387,7 +387,7 @@ static struct sk_buff *page_to_skb(struct virtnet_info *vi,
>>>    	unsigned int copy, hdr_len, hdr_padded_len;
>>>    	struct page *page_to_free = NULL;
>>>    	int tailroom, shinfo_size;
>>> -	char *p, *hdr_p;
>>> +	char *p, *hdr_p, *buf;
>>>
>>>    	p = page_address(page) + offset;
>>>    	hdr_p = p;
>>> @@ -403,11 +403,15 @@ static struct sk_buff *page_to_skb(struct virtnet_info *vi,
>>>    	 * space are aligned.
>>>    	 */
>>>    	if (headroom) {
>>> -		/* The actual allocated space size is PAGE_SIZE. */
>>> +		/* Buffers with headroom use PAGE_SIZE as alloc size,
>>> +		 * see add_recvbuf_mergeable() + get_mergeable_buf_len()
>>> +		 */
>>>    		truesize = PAGE_SIZE;
>>>    		tailroom = truesize - len - offset;
>>> +		buf = page_address(page);
>>>    	} else {
>>>    		tailroom = truesize - len;
>>> +		buf = p;
>>>    	}
>>>
>>>    	len -= hdr_len;
>>> @@ -416,11 +420,13 @@ static struct sk_buff *page_to_skb(struct virtnet_info *vi,
>>>
>>>    	shinfo_size = SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
>>>
>>> +	/* copy small packet so we can reuse these pages */
>>>    	if (!NET_IP_ALIGN && len > GOOD_COPY_LEN && tailroom >= shinfo_size) {
>>> -		skb = build_skb(p, truesize);
>>> +		skb = build_skb(buf, truesize);
>>>    		if (unlikely(!skb))
>>>    			return NULL;
>>>
>>> +		skb_reserve(skb, p - buf);
>>>    		skb_put(skb, len);
>>>    		goto ok;
>>>    	}