diff --git a/hw/net/tulip.c b/hw/net/tulip.c
index cfac271..1295f51 100644
--- a/hw/net/tulip.c
+++ b/hw/net/tulip.c
@@ -170,6 +170,10 @@
         } else {
             len = s->rx_frame_len;
         }
+
+        if (s->rx_frame_len + len > sizeof(s->rx_frame)) {
+            return;
+        }
         pci_dma_write(&s->dev, desc->buf_addr1, s->rx_frame +
             (s->rx_frame_size - s->rx_frame_len), len);
         s->rx_frame_len -= len;
@@ -181,6 +185,10 @@
         } else {
             len = s->rx_frame_len;
         }
+
+        if (s->rx_frame_len + len > sizeof(s->rx_frame)) {
+            return;
+        }
         pci_dma_write(&s->dev, desc->buf_addr2, s->rx_frame +
             (s->rx_frame_size - s->rx_frame_len), len);
         s->rx_frame_len -= len;
@@ -227,7 +235,8 @@
 
     trace_tulip_receive(buf, size);
 
-    if (size < 14 || size > 2048 || s->rx_frame_len || tulip_rx_stopped(s)) {
+    if (size < 14 || size > sizeof(s->rx_frame) - 4
+        || s->rx_frame_len || tulip_rx_stopped(s)) {
         return 0;
     }
 
@@ -275,7 +284,6 @@
     return tulip_receive(qemu_get_nic_opaque(nc), buf, size);
 }
 
-
 static NetClientInfo net_tulip_info = {
     .type = NET_CLIENT_DRIVER_NIC,
     .size = sizeof(NICState),
@@ -558,7 +566,7 @@
         if ((s->csr[6] >> CSR6_OM_SHIFT) & CSR6_OM_MASK) {
             /* Internal or external Loopback */
             tulip_receive(s, s->tx_frame, s->tx_frame_len);
-        } else {
+        } else if (s->tx_frame_len <= sizeof(s->tx_frame)) {
             qemu_send_packet(qemu_get_queue(s->nic),
                 s->tx_frame, s->tx_frame_len);
         }
@@ -570,23 +578,31 @@
     }
 }
 
-static void tulip_copy_tx_buffers(TULIPState *s, struct tulip_descriptor *desc)
+static int tulip_copy_tx_buffers(TULIPState *s, struct tulip_descriptor *desc)
 {
     int len1 = (desc->control >> TDES1_BUF1_SIZE_SHIFT) & TDES1_BUF1_SIZE_MASK;
     int len2 = (desc->control >> TDES1_BUF2_SIZE_SHIFT) & TDES1_BUF2_SIZE_MASK;
 
+    if (s->tx_frame_len + len1 > sizeof(s->tx_frame)) {
+        return -1;
+    }
     if (len1) {
         pci_dma_read(&s->dev, desc->buf_addr1,
             s->tx_frame + s->tx_frame_len, len1);
         s->tx_frame_len += len1;
     }
 
+    if (s->tx_frame_len + len2 > sizeof(s->tx_frame)) {
+        return -1;
+    }
     if (len2) {
         pci_dma_read(&s->dev, desc->buf_addr2,
             s->tx_frame + s->tx_frame_len, len2);
         s->tx_frame_len += len2;
     }
     desc->status = (len1 + len2) ? 0 : 0x7fffffff;
+
+    return 0;
 }
 
 static void tulip_setup_filter_addr(TULIPState *s, uint8_t *buf, int n)
@@ -651,13 +667,15 @@
 
 static void tulip_xmit_list_update(TULIPState *s)
 {
+#define TULIP_DESC_MAX 128
+    uint8_t i = 0;
     struct tulip_descriptor desc;
 
     if (tulip_ts(s) != CSR5_TS_SUSPENDED) {
         return;
     }
 
-    for (;;) {
+    for (i = 0; i < TULIP_DESC_MAX; i++) {
         tulip_desc_read(s, s->current_tx_desc, &desc);
         tulip_dump_tx_descriptor(s, &desc);
 
@@ -675,10 +693,10 @@
                 s->tx_frame_len = 0;
             }
 
-            tulip_copy_tx_buffers(s, &desc);
-
-            if (desc.control & TDES1_LS) {
-                tulip_tx(s, &desc);
+            if (!tulip_copy_tx_buffers(s, &desc)) {
+                if (desc.control & TDES1_LS) {
+                    tulip_tx(s, &desc);
+                }
             }
         }
         tulip_desc_write(s, s->current_tx_desc, &desc);