Re: [PATCH] net/virtio: fix Rx checksum calculation

[Maxime Coquelin <maxime.coquelin@redhat.com>]

Hi,

On 12/18/24 08:34, Wangyunjian(wangyunjian,TongTu) wrote:
>> -----Original Message-----
>> From: Maxime Coquelin [mailto:maxime.coquelin@redhat.com]
>> Sent: Tuesday, December 17, 2024 11:33 PM
>> To: dev@dpdk.org
>> Cc: Olivier Matz <olivier.matz@6wind.com>; Maxime Gouin
>> <maxime.gouin@6wind.com>; Maxime Coquelin
>> <maxime.coquelin@redhat.com>
>> Subject: [PATCH] net/virtio: fix Rx checksum calculation
>>
>> From: Olivier Matz <olivier.matz@6wind.com>
>>
>> If hdr->csum_start is larger than packet length, the len argument passed
>> to rte_raw_cksum_mbuf() overflows and causes a segmentation fault.
>>
>> Ignore checksum computation in this case.
>>
>> CVE-2024-11614
>>
>> Fixes: ca7036b4af3a ("vhost: fix offload flags in Rx path")
>>
>> Signed-off-by: Maxime Gouin <maxime.gouin@6wind.com>
>> Signed-off-by: Olivier Matz <olivier.matz@6wind.com>
>> Reviewed-by: Maxime Coquelin <maxime.coquelin@redhat.com>
>> ---
>>   lib/vhost/virtio_net.c | 3 +++
>>   1 file changed, 3 insertions(+)
>>
>> diff --git a/lib/vhost/virtio_net.c b/lib/vhost/virtio_net.c
>> index d764d4bc6a..69901ab3b5 100644
>> --- a/lib/vhost/virtio_net.c
>> +++ b/lib/vhost/virtio_net.c
>> @@ -2823,6 +2823,9 @@ vhost_dequeue_offload(struct virtio_net *dev,
>> struct virtio_net_hdr *hdr,
>>   			 */
>>   			uint16_t csum = 0, off;
>>
>> +			if (hdr->csum_start >= rte_pktmbuf_pkt_len(m))
>> +				return;
>> +
> 
> The hdr->csum_start does two successive reads from user space to read
> a variable length data structure. The result overflow if the data structure
> changes between the two reads.
> 
> We can prevent double fetch issue by using the temporary variable csum_start.

Right, that's a good catch! The exploitation od this issue seem
difficult though.

We may systematically copy the full header, as we only do it for ones
not contiguous in host VA space.

What do you think? Are you willing to contribute a fix?

Thanks,
Maxime
> 
> Thanks,
> Yunjian
> 
>>   			if (rte_raw_cksum_mbuf(m, hdr->csum_start,
>>   					rte_pktmbuf_pkt_len(m) - hdr->csum_start, &csum) <
>> 0)
>>   				return;
>> --
>> 2.47.0
>