From: Stefan Hajnoczi <stefanha@redhat.com>
Date: Wed, 15 Jul 2015 17:16:58 +0000 (+0100)
Subject: rtl8139: avoid nested ifs in IP header parsing
X-Git-Tag: xen-4.7.0~8
X-Git-Url: http://xenbits.xensource.com/gitweb?a=commitdiff_plain;h=e1a6f9038069494d43604eb00e5ff8eb5e83e389;p=qemu-xen-unstable.git

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>
[Backport to qemu-xen-tradition]
Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
---

diff --git a/hw/rtl8139.c b/hw/rtl8139.c
index 20e486a4e7..44c221c401 100644
--- a/hw/rtl8139.c
+++ b/hw/rtl8139.c
@@ -2113,26 +2113,30 @@ 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)
             {
-                DEBUG_PRINT(("RTL8139: +++ C+ mode has IP packet\n"));
+                goto skip_offload;
+            }
 
-                /* not aligned */
-                eth_payload_data = saved_buffer + ETH_HLEN;
-                eth_payload_len  = saved_size   - ETH_HLEN;
+            DEBUG_PRINT(("RTL8139: +++ C+ mode has IP packet\n"));
 
-                ip = (ip_header*)eth_payload_data;
+            /* not aligned */
+            eth_payload_data = saved_buffer + ETH_HLEN;
+            eth_payload_len  = saved_size   - ETH_HLEN;
 
-                if (IP_HEADER_VERSION(ip) != IP_HEADER_VERSION_4) {
-                    DEBUG_PRINT(("RTL8139: +++ 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;
-                }
+            ip = (ip_header*)eth_payload_data;
+
+            if (IP_HEADER_VERSION(ip) != IP_HEADER_VERSION_4) {
+                DEBUG_PRINT(("RTL8139: +++ 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)
@@ -2315,6 +2319,7 @@ static int rtl8139_cplus_transmit_one(RTL8139State *s)
             }
         }
 
+skip_offload:
         /* update tally counter */
         ++s->tally_counters.TxOk;