Re: [Qemu-devel] [PATCH v2] net: mipsnet: check transmit buffer size before sending

[Jason Wang <jasowang@redhat.com>]

On 2016年06月08日 18:37, P J P wrote:
> From: Prasad J Pandit <pjp@fedoraproject.org>
>
> When processing MIPSnet I/O port write operation, it uses a
> transmit buffer tx_buffer[MAX_ETH_FRAME_SIZE=1514]. Two indices
> 's->tx_written' and 's->tx_count' are used to control data written
> to this buffer. If the two were to be equal before writing, it'd
> lead to an OOB write access beyond tx_buffer. Add check to avoid it.
>
> Reported-by: Li Qiang <qiang6-s@360.cn>
> Signed-off-by: Prasad J Pandit <pjp@fedoraproject.org>
> ---
>   hw/net/mipsnet.c | 8 +++++---
>   1 file changed, 5 insertions(+), 3 deletions(-)
>
> Update as per:
>    -> https://lists.gnu.org/archive/html/qemu-devel/2016-06/msg02089.html
>
> diff --git a/hw/net/mipsnet.c b/hw/net/mipsnet.c
> index 740cd98..450e42d 100644
> --- a/hw/net/mipsnet.c
> +++ b/hw/net/mipsnet.c
> @@ -180,10 +180,12 @@ static void mipsnet_ioport_write(void *opaque, hwaddr addr,
>           break;
>       case MIPSNET_TX_DATA_BUFFER:
>           s->tx_buffer[s->tx_written++] = val;

I believe we may still have a buffer overflow here, no?

> -        if (s->tx_written == s->tx_count) {
> +        if ((s->tx_written >= MAX_ETH_FRAME_SIZE)
> +            || (s->tx_written == s->tx_count)) {
>               /* Send buffer. */
> -            trace_mipsnet_send(s->tx_count);
> -            qemu_send_packet(qemu_get_queue(s->nic), s->tx_buffer, s->tx_count);
> +            trace_mipsnet_send(s->tx_written);
> +            qemu_send_packet(qemu_get_queue(s->nic),
> +                                s->tx_buffer, s->tx_written);
>               s->tx_count = s->tx_written = 0;
>               s->intctl |= MIPSNET_INTCTL_TXDONE;
>               s->busy = 1;