Re: [Qemu-stable] [Qemu-devel] [PATCH 5/5] virtio-net: unbreak any layout

[Jason Wang]

On 07/13/2015 03:24 PM, Michael S. Tsirkin wrote:
> On Mon, Jul 13, 2015 at 01:46:51PM +0800, Jason Wang wrote:
>> Commit 032a74a1c0fcdd5fd1c69e56126b4c857ee36611
>> ("virtio-net: byteswap virtio-net header") breaks any layout by
>> requiring out_sg[0].iov_len >= n->guest_hdr_len. Fixing this by
>> copying header to temporary buffer and copying it back after byteswap.
>>
>> Fixes 032a74a1c0fcdd5fd1c69e56126b4c857ee36611
>> ("virtio-net: byteswap virtio-net header")
>> Cc: address@hidden
>> Cc: address@hidden
>> Signed-off-by: Jason Wang <address@hidden>
>> ---
>>  hw/net/virtio-net.c | 10 +++++++---
>>  1 file changed, 7 insertions(+), 3 deletions(-)
>>
>> diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c
>> index e3c2db3..b42af8f 100644
>> --- a/hw/net/virtio-net.c
>> +++ b/hw/net/virtio-net.c
>> @@ -1139,10 +1139,11 @@ static int32_t virtio_net_flush_tx(VirtIONetQueue *q)
>>      }
>>  
>>      while (virtqueue_pop(q->tx_vq, &elem)) {
>> -        ssize_t ret, len;
>> +        ssize_t ret, len, s;
>>          unsigned int out_num = elem.out_num;
>>          struct iovec *out_sg = &elem.out_sg[0];
>>          struct iovec sg[VIRTQUEUE_MAX_SIZE];
>> +        struct virtio_net_hdr hdr;
>>  
>>          if (out_num < 1) {
>>              error_report("virtio-net header not in first element");
>> @@ -1150,11 +1151,14 @@ static int32_t virtio_net_flush_tx(VirtIONetQueue *q)
>>          }
>>  
>>          if (n->has_vnet_hdr) {
>> -            if (out_sg[0].iov_len < n->guest_hdr_len) {
>> +            s = iov_to_buf(out_sg, out_num, 0, &hdr, sizeof(hdr));
>> +            if (s != sizeof(hdr)) {
>>                  error_report("virtio-net header incorrect");
>>                  exit(1);
>>              }
>> -            virtio_net_hdr_swap(vdev, (void *) out_sg[0].iov_base);
>> +            virtio_net_hdr_swap(vdev, (void *) &hdr);
>> +            s = iov_from_buf(out_sg, out_num, 0, &hdr, sizeof(hdr));
>> +            assert(s == sizeof(hdr));
>>          }
>>  
>>          /*
> Looks like this will write into out_sg - that's violating the virtio spec.

Right, will fix this in V2.

Thanks
>
>> -- 
>> 2.1.4