From: Prasad J Pandit <pjp@fedoraproject.org>

Define .can_receive routine to do sanity checks before receiving
packet data.

Signed-off-by: Prasad J Pandit <pjp@fedoraproject.org>
---
 hw/net/tulip.c | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

Update v3: define .can_receive routine
  -> https://lists.gnu.org/archive/html/qemu-devel/2020-02/msg06275.html

diff --git a/hw/net/tulip.c b/hw/net/tulip.c
index fbe40095da..757f12c710 100644
--- a/hw/net/tulip.c
+++ b/hw/net/tulip.c
@@ -229,6 +229,18 @@ static bool tulip_filter_address(TULIPState *s, const uint8_t *addr)
     return ret;
 }
 
+static int
+tulip_can_receive(NetClientState *nc)
+{
+    TULIPState *s = qemu_get_nic_opaque(nc);
+
+    if (s->rx_frame_len || tulip_rx_stopped(s)) {
+        return false;
+    }
+
+    return true;
+}
+
 static ssize_t tulip_receive(TULIPState *s, const uint8_t *buf, size_t size)
 {
     struct tulip_descriptor desc;
@@ -236,7 +248,7 @@ static ssize_t tulip_receive(TULIPState *s, const uint8_t *buf, size_t size)
     trace_tulip_receive(buf, size);
 
     if (size < 14 || size > sizeof(s->rx_frame) - 4
-        || s->rx_frame_len || tulip_rx_stopped(s)) {
+        || !tulip_can_receive(s->nic->ncs)) {
         return 0;
     }
 
@@ -288,6 +300,7 @@ static NetClientInfo net_tulip_info = {
     .type = NET_CLIENT_DRIVER_NIC,
     .size = sizeof(NICState),
     .receive = tulip_receive_nc,
+    .can_receive = tulip_can_receive,
 };
 
 static const char *tulip_reg_name(const hwaddr addr)
-- 
2.24.1

On Tue, Mar 03, 2020 at 04:17:24PM +0530, P J P wrote:
> diff --git a/hw/net/tulip.c b/hw/net/tulip.c
> index fbe40095da..757f12c710 100644
> --- a/hw/net/tulip.c
> +++ b/hw/net/tulip.c
> @@ -229,6 +229,18 @@ static bool tulip_filter_address(TULIPState *s, const uint8_t *addr)
>      return ret;
>  }
>  
> +static int
> +tulip_can_receive(NetClientState *nc)
> +{
> +    TULIPState *s = qemu_get_nic_opaque(nc);
> +
> +    if (s->rx_frame_len || tulip_rx_stopped(s)) {
> +        return false;
> +    }
> +
> +    return true;
> +}

Are the required qemu_flush_queued_packets() calls in place so that
packet transfer wakes up again when .can_receive() transitions from
false to true?

(If qemu_flush_queued_packets() is missing then transmission hangs after
.can_receive() becomes false.)

Stefan

  Hello Stefan, Jason,

+-- On Fri, 6 Mar 2020, Stefan Hajnoczi wrote --+
| > +static int
| > +tulip_can_receive(NetClientState *nc)
| > +{
| > +    TULIPState *s = qemu_get_nic_opaque(nc);
| > +
| > +    if (s->rx_frame_len || tulip_rx_stopped(s)) {
| > +        return false;
| > +    }
| > +
| > +    return true;
| > +}
| 
| Are the required qemu_flush_queued_packets() calls in place so that
| packet transfer wakes up again when .can_receive() transitions from
| false to true?

  Yes, qemu_flush_queued_packets() calls are in tulip_write(). Do we need to 
call tulip_can_receive() before each call?

Thank you.
--
Prasad J Pandit / Red Hat Product Security Team
8685 545E B54C 486B C6EB 271E E285 8B5A F050 DE8D

On 2020/3/17 上午2:01, P J P wrote:
>    Hello Stefan, Jason,
>
> +-- On Fri, 6 Mar 2020, Stefan Hajnoczi wrote --+
> | > +static int
> | > +tulip_can_receive(NetClientState *nc)
> | > +{
> | > +    TULIPState *s = qemu_get_nic_opaque(nc);
> | > +
> | > +    if (s->rx_frame_len || tulip_rx_stopped(s)) {
> | > +        return false;
> | > +    }
> | > +
> | > +    return true;
> | > +}
> |
> | Are the required qemu_flush_queued_packets() calls in place so that
> | packet transfer wakes up again when .can_receive() transitions from
> | false to true?
>
>    Yes, qemu_flush_queued_packets() calls are in tulip_write(). Do we need to
> call tulip_can_receive() before each call?


Probably not, just need to make sure the check in tulip_rx_stopped(s) 
matches the action that triggers qemu_flush_queued_packets() in 
tulip_write() is sufficient.

This to make sure net core can restore the receiving.

Btw, what's the point of checking rx_frame_len here?

Thanks


>
> Thank you.
> --
> Prasad J Pandit / Red Hat Product Security Team
> 8685 545E B54C 486B C6EB 271E E285 8B5A F050 DE8D

+-- On Tue, 17 Mar 2020, Jason Wang wrote --+
| > +-- On Fri, 6 Mar 2020, Stefan Hajnoczi wrote --+
| > | > +static int
| > | > +tulip_can_receive(NetClientState *nc)
| > | > +{
| > | > +    TULIPState *s = qemu_get_nic_opaque(nc);
| > | > +
| > | > +    if (s->rx_frame_len || tulip_rx_stopped(s)) {
| > | > +        return false;
| > | > +    }
|
| Btw, what's the point of checking rx_frame_len here?

tulip_can_recive() is called from tulip_receive(). IIUC non zero(0) 
'rx_frame_len' hints that s->rs_frame[] buffer still has unread data bytes and 
it can not receive new bytes. The check was earlier in tulip_receive().

Thank you.
--
Prasad J Pandit / Red Hat Product Security Team
8685 545E B54C 486B C6EB 271E E285 8B5A F050 DE8D

On 2020/3/17 下午6:49, P J P wrote:
> +-- On Tue, 17 Mar 2020, Jason Wang wrote --+
> | > +-- On Fri, 6 Mar 2020, Stefan Hajnoczi wrote --+
> | > | > +static int
> | > | > +tulip_can_receive(NetClientState *nc)
> | > | > +{
> | > | > +    TULIPState *s = qemu_get_nic_opaque(nc);
> | > | > +
> | > | > +    if (s->rx_frame_len || tulip_rx_stopped(s)) {
> | > | > +        return false;
> | > | > +    }
> |
> | Btw, what's the point of checking rx_frame_len here?
>
> tulip_can_recive() is called from tulip_receive(). IIUC non zero(0)
> 'rx_frame_len' hints that s->rs_frame[] buffer still has unread data bytes and
> it can not receive new bytes. The check was earlier in tulip_receive().


Right, so need to make sure qemu_flush_ququed_packets() was called when 
rx_frame_len is zero.

Thanks



>
> Thank you.
> --
> Prasad J Pandit / Red Hat Product Security Team
> 8685 545E B54C 486B C6EB 271E E285 8B5A F050 DE8D

  Hello Jason,

+-- On Wed, 18 Mar 2020, Jason Wang wrote --+
| Right, so need to make sure qemu_flush_ququed_packets() was called when 
| rx_frame_len is zero.

  Sent patch v4, with this call. Please see when you've time.

Thank you.
--
Prasad J Pandit / Red Hat Product Security Team
8685 545E B54C 486B C6EB 271E E285 8B5A F050 DE8D