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 ee3b6903a11b06630bfcad586a9e80950e97e58d..ba453045387ac2a46387b8fc6762b0c9afcc545c 100644 (file)
--- a/hw/net/rtl8139.c
+++ b/hw/net/rtl8139.c
@@ -2170,28 +2170,30 @@ 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)
@@ -2387,6 +2389,7 @@ static int rtl8139_cplus_transmit_one(RTL8139State *s)
             }
         }
 
+skip_offload:
         /* update tally counter */
         ++s->tally_counters.TxOk;