rtl8139: avoid nested ifs in IP header parsing

Transmit offload needs to parse packet headers.  If header fields have
unexpected values the offload processing is skipped.

The code currently uses nested ifs because there is relatively little
input validation.  The next patches will add missing input validation
and a goto label is more appropriate to avoid deep if statement nesting.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>

diff --git a/hw/net/rtl8139.c b/hw/net/rtl8139.c
index 5f0197c9df2ecf1c149380dcb47d93da96b8e0f4..91ba33bf2f47969260a5903494a331c3504337ba 100644 (file)
--- a/hw/net/rtl8139.c
+++ b/hw/net/rtl8139.c
@@ -2174,28 +2174,30 @@ static int rtl8139_cplus_transmit_one(RTL8139State *s)
             size_t   eth_payload_len  = 0;
 
             int proto = be16_to_cpu(*(uint16_t *)(saved_buffer + 12));
-            if (proto == ETH_P_IP)
+            if (proto != ETH_P_IP)
             {
-                DPRINTF("+++ C+ mode has IP packet\n");
-
-                /* not aligned */
-                eth_payload_data = saved_buffer + ETH_HLEN;
-                eth_payload_len  = saved_size   - ETH_HLEN;
-
-                ip = (ip_header*)eth_payload_data;
-
-                if (IP_HEADER_VERSION(ip) != IP_HEADER_VERSION_4) {
-                    DPRINTF("+++ C+ mode packet has bad IP version %d "
-                        "expected %d\n", IP_HEADER_VERSION(ip),
-                        IP_HEADER_VERSION_4);
-                    ip = NULL;
-                } else {
-                    hlen = IP_HEADER_LENGTH(ip);
-                    ip_protocol = ip->ip_p;
-                    ip_data_len = be16_to_cpu(ip->ip_len) - hlen;
-                }
+                goto skip_offload;
             }
 
+            DPRINTF("+++ C+ mode has IP packet\n");
+
+            /* not aligned */
+            eth_payload_data = saved_buffer + ETH_HLEN;
+            eth_payload_len  = saved_size   - ETH_HLEN;
+
+            ip = (ip_header*)eth_payload_data;
+
+            if (IP_HEADER_VERSION(ip) != IP_HEADER_VERSION_4) {
+                DPRINTF("+++ C+ mode packet has bad IP version %d "
+                    "expected %d\n", IP_HEADER_VERSION(ip),
+                    IP_HEADER_VERSION_4);
+                goto skip_offload;
+            }
+
+            hlen = IP_HEADER_LENGTH(ip);
+            ip_protocol = ip->ip_p;
+            ip_data_len = be16_to_cpu(ip->ip_len) - hlen;
+
             if (ip)
             {
                 if (txdw0 & CP_TX_IPCS)
@@ -2391,6 +2393,7 @@ static int rtl8139_cplus_transmit_one(RTL8139State *s)
             }
         }
 
+skip_offload:
         /* update tally counter */
         ++s->tally_counters.TxOk;