Handle DLT_NULL correctly - the AF_ value is in host byte order, which

[libpcap] / gencode.c

diff --git a/gencode.c b/gencode.c
index 5ce6da56380e8adff0368f05c95c683d731b125c..5d501270c1af9420efbf2d832cb8e9f55c3dad4f 100644 (file)
--- a/gencode.c
+++ b/gencode.c
@@ -21,7 +21,7 @@
  */
 #ifndef lint
 static const char rcsid[] =
-    "@(#) $Header: /tcpdump/master/libpcap/gencode.c,v 1.138 2000-12-12 08:08:38 guy Exp $ (LBL)";
+    "@(#) $Header: /tcpdump/master/libpcap/gencode.c,v 1.139 2000-12-16 21:31:10 guy Exp $ (LBL)";
 #endif
 
 #ifdef HAVE_CONFIG_H
@@ -578,6 +578,7 @@ init_linktype(type)
                return;
 
        case DLT_NULL:
+       case DLT_LOOP:
                off_linktype = 0;
                off_nl = 4;
                return;
@@ -689,6 +690,14 @@ gen_false()
        return gen_uncond(0);
 }
 
+/*
+ * Byte-swap a 32-bit number.
+ * ("htonl()" or "ntohl()" won't work - we want to byte-swap even on
+ * big-endian platforms.)
+ */
+#define        SWAPLONG(y) \
+((((y)&0xff)<<24) | (((y)&0xff00)<<8) | (((y)&0xff0000)>>8) | (((y)>>24)&0xff))
+
 static struct block *
 gen_linktype(proto)
        register int proto;
@@ -843,15 +852,66 @@ gen_linktype(proto)
                break;
 
        case DLT_NULL:
-               /* XXX */
-               if (proto == ETHERTYPE_IP)
-                       return (gen_cmp(0, BPF_W, (bpf_int32)htonl(AF_INET)));
+       case DLT_LOOP:
+               /*
+                * For DLT_NULL, the link-layer header is a 32-bit
+                * word containing an AF_ value in *host* byte order.
+                *
+                * In addition, if we're reading a saved capture file,
+                * the host byte order in the capture may not be the
+                * same as the host byte order on this machine.
+                *
+                * For DLT_LOOP, the link-layer header is a 32-bit
+                * word containing an AF_ value in *network* byte order.
+                *
+                * XXX - AF_ values may, unfortunately, be platform-
+                * dependent; for example, FreeBSD's AF_INET6 is 24
+                * whilst NetBSD's and OpenBSD's is 26.
+                *
+                * This means that, when reading a capture file, just
+                * checking for our AF_INET6 value won't work if the
+                * capture file came from another OS.
+                */
+               switch (proto) {
+
+               case ETHERTYPE_IP:
+                       proto = AF_INET;
+                       break;
+
 #ifdef INET6
-               else if (proto == ETHERTYPE_IPV6)
-                       return (gen_cmp(0, BPF_W, (bpf_int32)htonl(AF_INET6)));
+               case ETHERTYPE_IPV6:
+                       proto = AF_INET6;
+                       break;
 #endif
-               else
+
+               default:
+                       /*
+                        * Not a type on which we support filtering.
+                        * XXX - support those that have AF_ values
+                        * #defined on this platform, at least?
+                        */
                        return gen_false();
+               }
+
+               if (linktype == DLT_NULL) {
+                       /*
+                        * The AF_ value is in host byte order, but
+                        * the BPF interpreter will convert it to
+                        * network byte order.
+                        *
+                        * If this is a save file, and it's from a
+                        * machine with the opposite byte order to
+                        * ours, we byte-swap the AF_ value.
+                        *
+                        * Then we run it through "htonl()", and
+                        * generate code to compare against the result.
+                        */
+                       if (bpf_pcap->sf.rfile != NULL &&
+                           bpf_pcap->sf.swapped)
+                               proto = SWAPLONG(proto);
+                       proto = htonl(proto);
+               }
+               return (gen_cmp(0, BPF_W, (bpf_int32)proto));
        }
        return gen_cmp(off_linktype, BPF_H, (bpf_int32)proto);
 }
@@ -3117,10 +3177,24 @@ gen_inbound(dir)
 {
        register struct block *b0;
 
-       b0 = gen_relation(BPF_JEQ,
+       /*
+        * Only some data link types support inbound/outbound qualifiers.
+        */
+       switch (linktype) {
+       case DLT_SLIP:
+       case DLT_PPP:
+               b0 = gen_relation(BPF_JEQ,
                          gen_load(Q_LINK, gen_loadi(0), 1),
                          gen_loadi(0),
                          dir);
+               break;
+
+       default:
+               bpf_error("inbound/outbound not supported on linktype %d\n",
+                   linktype);
+               b0 = NULL;
+               /* NOTREACHED */
+       }
        return (b0);
 }