Re: [PATCH] virtio-net: correctly copy vnet header when flushing TX

[Mauro Matteo Cascella]

On Tue, Jan 2, 2024 at 12:20 PM Yuri Benditovich
<yuri.benditovich@daynix.com> wrote:
>
> I agree, thank you.
>
> Where is this CVE-2023-6693 available?

Here: https://bugzilla.redhat.com/show_bug.cgi?id=2254580.

> Thanks,
> Yuri
>
> On Tue, Jan 2, 2024 at 5:29 AM Jason Wang <jasowang@redhat.com> wrote:
>>
>> When HASH_REPORT is negotiated, the guest_hdr_len might be larger than
>> the size of the mergeable rx buffer header. Using
>> virtio_net_hdr_mrg_rxbuf during the header swap might lead a stack
>> overflow in this case. Fixing this by using virtio_net_hdr_v1_hash
>> instead.
>>
>> Reported-by: Xiao Lei <leixiao.nop@zju.edu.cn>
>> Cc: Yuri Benditovich <yuri.benditovich@daynix.com>
>> Cc: qemu-stable@nongnu.org
>> Cc: Mauro Matteo Cascella <mcascell@redhat.com>
>> Fixes: CVE-2023-6693
>> Fixes: e22f0603fb2f ("virtio-net: reference implementation of hash report")
>> Signed-off-by: Jason Wang <jasowang@redhat.com>
>> ---
>>  hw/net/virtio-net.c | 13 +++++++++----
>>  1 file changed, 9 insertions(+), 4 deletions(-)
>>
>> diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c
>> index 80c56f0cfc..73024babd4 100644
>> --- a/hw/net/virtio-net.c
>> +++ b/hw/net/virtio-net.c
>> @@ -674,6 +674,11 @@ static void virtio_net_set_mrg_rx_bufs(VirtIONet *n, 
>> int mergeable_rx_bufs,
>>
>>      n->mergeable_rx_bufs = mergeable_rx_bufs;
>>
>> +    /*
>> +     * Note: when extending the vnet header, please make sure to
>> +     * change the vnet header copying logic in virtio_net_flush_tx()
>> +     * as well.
>> +     */
>>      if (version_1) {
>>          n->guest_hdr_len = hash_report ?
>>              sizeof(struct virtio_net_hdr_v1_hash) :
>> @@ -2693,7 +2698,7 @@ static int32_t virtio_net_flush_tx(VirtIONetQueue *q)
>>          ssize_t ret;
>>          unsigned int out_num;
>>          struct iovec sg[VIRTQUEUE_MAX_SIZE], sg2[VIRTQUEUE_MAX_SIZE + 1], 
>> *out_sg;
>> -        struct virtio_net_hdr_mrg_rxbuf mhdr;
>> +        struct virtio_net_hdr_v1_hash vhdr;
>>
>>          elem = virtqueue_pop(q->tx_vq, sizeof(VirtQueueElement));
>>          if (!elem) {
>> @@ -2710,7 +2715,7 @@ static int32_t virtio_net_flush_tx(VirtIONetQueue *q)
>>          }
>>
>>          if (n->has_vnet_hdr) {
>> -            if (iov_to_buf(out_sg, out_num, 0, &mhdr, n->guest_hdr_len) <
>> +            if (iov_to_buf(out_sg, out_num, 0, &vhdr, n->guest_hdr_len) <
>>                  n->guest_hdr_len) {
>>                  virtio_error(vdev, "virtio-net header incorrect");
>>                  virtqueue_detach_element(q->tx_vq, elem, 0);
>> @@ -2718,8 +2723,8 @@ static int32_t virtio_net_flush_tx(VirtIONetQueue *q)
>>                  return -EINVAL;
>>              }
>>              if (n->needs_vnet_hdr_swap) {
>> -                virtio_net_hdr_swap(vdev, (void *) &mhdr);
>> -                sg2[0].iov_base = &mhdr;
>> +                virtio_net_hdr_swap(vdev, (void *) &vhdr);
>> +                sg2[0].iov_base = &vhdr;
>>                  sg2[0].iov_len = n->guest_hdr_len;
>>                  out_num = iov_copy(&sg2[1], ARRAY_SIZE(sg2) - 1,
>>                                     out_sg, out_num,
>> --
>> 2.42.0
>>

-- 
Mauro Matteo Cascella
Red Hat Product Security
PGP-Key ID: BB3410B0