From: Peter Maydell <peter.maydell@linaro.org>

The xilinx_ethlite network device wasn't checking that the TX packet
size set by the guest was within the size of its dual port RAM, with
the effect that the guest could get it to read off the end of the RAM
block.

Check the length.  There is no provision in this very simple device
for reporting errors, so as with various RX errors we just report via
tracepoint.

This lack of length check has been present since the device was first
introduced, though the code implementing the tx path has changed
somewhat since then.

Cc: qemu-stable@nongnu.org
Resolves: https://gitlab.com/qemu-project/qemu/-/issues/3317
Fixes: b43848a1005ce ("xilinx: Add ethlite emulation")
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Reviewed-by: Edgar E. Iglesias <edgar.iglesias@amd.com>
Message-ID: <20260303172718.437015-1-peter.maydell@linaro.org>
[PMD: renamed size -> tx_size to avoid shadow=compatible-local error]
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
---
 hw/net/xilinx_ethlite.c | 12 +++++++++---
 hw/net/trace-events     |  1 +
 2 files changed, 10 insertions(+), 3 deletions(-)

diff --git a/hw/net/xilinx_ethlite.c b/hw/net/xilinx_ethlite.c
index ba3acd4c77c..7ea194475f1 100644
--- a/hw/net/xilinx_ethlite.c
+++ b/hw/net/xilinx_ethlite.c
@@ -162,9 +162,15 @@ static void port_tx_write(void *opaque, hwaddr addr, uint64_t value,
         break;
     case TX_CTRL:
         if ((value & (CTRL_P | CTRL_S)) == CTRL_S) {
-            qemu_send_packet(qemu_get_queue(s->nic),
-                             txbuf_ptr(s, port_index),
-                             s->port[port_index].reg.tx_len);
+            uint32_t tx_size = s->port[port_index].reg.tx_len;
+
+            if (tx_size >= BUFSZ_MAX) {
+                trace_ethlite_pkt_tx_size_too_big(tx_size);
+            } else {
+                qemu_send_packet(qemu_get_queue(s->nic),
+                                 txbuf_ptr(s, port_index),
+                                 tx_size);
+            }
             if (s->port[port_index].reg.tx_ctrl & CTRL_I) {
                 eth_pulse_irq(s);
             }
diff --git a/hw/net/trace-events b/hw/net/trace-events
index 23efa91d055..001a20b0e2a 100644
--- a/hw/net/trace-events
+++ b/hw/net/trace-events
@@ -527,3 +527,4 @@ xen_netdev_rx(int dev, int idx, int status, int flags) "vif%u idx %d status %d f
 # xilinx_ethlite.c
 ethlite_pkt_lost(uint32_t rx_ctrl) "rx_ctrl:0x%" PRIx32
 ethlite_pkt_size_too_big(uint64_t size) "size:0x%" PRIx64
+ethlite_pkt_tx_size_too_big(uint64_t size) "size:0x%" PRIx64
-- 
2.53.0