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>

diff --git a/hw/rtl8139.c b/hw/rtl8139.c
index aa8ed0a919d8ef7ab3a0ce6e647fff0366d6413e..ab1914cded4a3b72b7d114c8ab4b8ff33a0a2d81 100644 (file)
--- a/hw/rtl8139.c
+++ b/hw/rtl8139.c
@@ -2169,28 +2169,30 @@ 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)
@@ -2386,6 +2388,7 @@ static int rtl8139_cplus_transmit_one(RTL8139State *s)
             }
         }
 
+skip_offload:
         /* update tally counter */
         ++s->tally_counters.TxOk;