fix cksum mismatch

lhyqy5 · Dec 5, 2015 · bc0c26a · bc0c26a
1 parent 84135b1
commit bc0c26a
Showing 1 changed file with 37 additions and 0 deletions.
diff --git a/src/nat.c b/src/nat.c
@@ -132,6 +132,34 @@ typedef struct {
   } \
 }
 
+#define FIX_CHECKSUM(iphdr, fcc) { \
+  short sum = 0; \
+  int32_t verify = 0; \
+  verify = (iphdr->ver<<8)+ \
+  iphdr->tos+ \
+  htons(iphdr->total_len)+ \
+  htons(iphdr->id)+ \
+  htons(iphdr->frag)+ \
+  (iphdr->ttl<<8)+ \
+  iphdr->proto+ \
+  htons(iphdr->checksum)+ \
+  htons((iphdr->saddr>>16) & 0xffff)+ \
+  htons(iphdr->saddr & 0xffff)+ \
+  htons((iphdr->daddr>>16) & 0xffff)+ \
+  htons(iphdr->daddr & 0xffff); \
+  verify = (verify>>16) + (verify&0xffff); \
+  sum = ntohs(verify); \
+  logf("cksum verify:0x%x, checksum:%x", verify, sum); \
+  if(sum == -1){ \
+    fcc = 0; \
+  } else { \
+    fcc = sum<-1 ? -sum-1 : -sum; \
+    if(fcc == 1 || fcc == -1){ \
+      iphdr->checksum += fcc; \
+    } \
+  } \
+}
+
 int nat_fix_upstream(nat_ctx_t *ctx, unsigned char *buf, size_t buflen,
                      const struct sockaddr *addr, socklen_t addrlen) {
   uint8_t iphdr_len;
@@ -169,7 +197,10 @@ int nat_fix_upstream(nat_ctx_t *ctx, unsigned char *buf, size_t buflen,
 
   // add old, sub new
   acc = client->input_tun_ip - iphdr->saddr;
+
+  short fcc = 0;
   ADJUST_CHECKSUM(acc, iphdr->checksum);
+  FIX_CHECKSUM(iphdr, fcc);
 
   if (0 == (iphdr->frag & htons(0x1fff))) {
     // only adjust tcp & udp when frag offset == 0
@@ -181,13 +212,15 @@ int nat_fix_upstream(nat_ctx_t *ctx, unsigned char *buf, size_t buflen,
       }
       tcp_hdr_t *tcphdr = ip_payload;
       ADJUST_CHECKSUM(acc, tcphdr->checksum);
+      tcphdr->checksum += fcc;
     } else if (iphdr->proto == IPPROTO_UDP) {
       if (buflen < iphdr_len + 8) {
         errf("nat: udp packet too short");
         return -1;
       }
       udp_hdr_t *udphdr = ip_payload;
       ADJUST_CHECKSUM(acc, udphdr->checksum);
+      udphdr->checksum += fcc;
     }
   }
   return 0;
@@ -234,7 +267,9 @@ int nat_fix_downstream(nat_ctx_t *ctx, unsigned char *buf, size_t buflen,
   // overwrite IP
   iphdr->daddr = client->input_tun_ip;
 
+  short fcc = 0;
   ADJUST_CHECKSUM(acc, iphdr->checksum);
+  FIX_CHECKSUM(iphdr, fcc);
 
   if (0 == (iphdr->frag & htons(0x1fff))) {
     // only adjust tcp & udp when frag offset == 0
@@ -246,13 +281,15 @@ int nat_fix_downstream(nat_ctx_t *ctx, unsigned char *buf, size_t buflen,
       }
       tcp_hdr_t *tcphdr = ip_payload;
       ADJUST_CHECKSUM(acc, tcphdr->checksum);
+      tcphdr->checksum += fcc;
     } else if (iphdr->proto == IPPROTO_UDP) {
       if (buflen < iphdr_len + 8) {
         errf("nat: udp packet too short");
         return -1;
       }
       udp_hdr_t *udphdr = ip_payload;
       ADJUST_CHECKSUM(acc, udphdr->checksum);
+      udphdr->checksum += fcc;
     }
   }
   return 0;