diff options
| -rw-r--r-- | c/netd.c | 91 | ||||
| -rw-r--r-- | tools/gateway.py | 28 |
2 files changed, 88 insertions, 31 deletions
@@ -1,47 +1,78 @@ #include "netlib.h" -/* netd - a minimal IP stack over SLIP. Milestone A: answer ICMP echo (ping). - Our address is 10.0.0.2; the SLIP peer (gateway) is 10.0.0.1. +/* netd - a minimal IP stack over SLIP. Our address is 10.0.0.2, peer 10.0.0.1. + Milestones: A) ICMP echo, B) UDP echo. Raw byte arrays, network byte order + (big-endian) handled explicitly. */ - Everything is done on raw byte arrays so endianness is explicit (network - byte order = big-endian): field[hi], field[lo]. */ +static unsigned char pkt[256]; -/* Internet checksum (RFC 1071): 16-bit one's-complement sum with carry fold. */ -static unsigned int cksum(unsigned char *d, unsigned char len) { - unsigned int sum = 0, w; - unsigned char i = 0; - while ((unsigned char)(i + 1) < len) { +/* one's-complement sum (RFC 1071) with a running seed, carry-folded each add */ +static unsigned int sum16(unsigned char *d, unsigned int len, unsigned int sum) { + unsigned int w, i = 0; + while (i + 1 < len) { w = ((unsigned int)d[i] << 8) | d[i + 1]; sum += w; if (sum < w) sum++; i += 2; } if (len & 1) { w = (unsigned int)d[len - 1] << 8; sum += w; if (sum < w) sum++; } - return ~sum; + return sum; } -void main(void) { - unsigned char pkt[128]; - unsigned char len, ihl, i, t; +/* pseudo-header sum for UDP/TCP: src+dst IP, protocol, segment length */ +static unsigned int pseudo(unsigned char proto, unsigned int seglen) { + unsigned int sum = sum16(pkt + 12, 8, 0), w; + w = proto; sum += w; if (sum < w) sum++; + w = seglen; sum += w; if (sum < w) sum++; + return sum; +} + +static void swap4(unsigned char a, unsigned char b) { + unsigned char i, t; + for (i = 0; i < 4; i++) { t = pkt[a + i]; pkt[a + i] = pkt[b + i]; pkt[b + i] = t; } +} +static void swap2(unsigned char a, unsigned char b) { + unsigned char t; + t = pkt[a]; pkt[a] = pkt[b]; pkt[b] = t; + t = pkt[a + 1]; pkt[a + 1] = pkt[b + 1]; pkt[b + 1] = t; +} + +/* recompute the IP header checksum over ihl bytes, then send 'len' total */ +static void ip_send(unsigned char ihl, unsigned int len) { unsigned int c; - puts("netd: IP/ICMP up (10.0.0.2)"); nl(); + pkt[10] = 0; pkt[11] = 0; + c = ~sum16(pkt, ihl, 0); + pkt[10] = (unsigned char)(c >> 8); pkt[11] = (unsigned char)c; + slip_send((char *)pkt, (unsigned char)len); +} + +void main(void) { + unsigned char len, ihl; + unsigned int c, seglen; + puts("netd: IP up (10.0.0.2)"); nl(); for (;;) { - len = slip_recv((char *)pkt, 127); - if (len < 28) continue; /* IP(20) + ICMP(8) minimum */ - if ((pkt[0] >> 4) != 4) continue; /* IPv4 only */ + len = slip_recv((char *)pkt, 255); + if (len < 20 || (pkt[0] >> 4) != 4) continue; ihl = (pkt[0] & 0x0f) << 2; - if (pkt[9] != 1) continue; /* protocol 1 = ICMP */ - if (pkt[ihl] != 8) continue; /* ICMP type 8 = echo request */ + pkt[8] = 64; /* TTL for any reply */ - /* turn the request into a reply, in place */ - for (i = 0; i < 4; i++) { t = pkt[12 + i]; pkt[12 + i] = pkt[16 + i]; pkt[16 + i] = t; } - pkt[8] = 64; /* reset TTL */ - pkt[ihl] = 0; /* ICMP type -> echo reply */ - pkt[ihl + 2] = 0; pkt[ihl + 3] = 0; /* recompute ICMP checksum */ - c = cksum(pkt + ihl, (unsigned char)(len - ihl)); - pkt[ihl + 2] = (unsigned char)(c >> 8); pkt[ihl + 3] = (unsigned char)c; - pkt[10] = 0; pkt[11] = 0; /* recompute IP header checksum */ - c = cksum(pkt, ihl); - pkt[10] = (unsigned char)(c >> 8); pkt[11] = (unsigned char)c; + if (pkt[9] == 1) { /* ICMP */ + if (len < (unsigned char)(ihl + 8) || pkt[ihl] != 8) continue; /* echo request */ + swap4(12, 16); + pkt[ihl] = 0; /* -> echo reply */ + pkt[ihl + 2] = 0; pkt[ihl + 3] = 0; + c = ~sum16(pkt + ihl, (unsigned int)(len - ihl), 0); + pkt[ihl + 2] = (unsigned char)(c >> 8); pkt[ihl + 3] = (unsigned char)c; + ip_send(ihl, len); - slip_send((char *)pkt, len); + } else if (pkt[9] == 17) { /* UDP echo */ + if (len < (unsigned char)(ihl + 8)) continue; + seglen = (unsigned int)(len - ihl); + swap4(12, 16); /* swap IP addresses */ + swap2(ihl, ihl + 2); /* swap UDP ports */ + pkt[ihl + 6] = 0; pkt[ihl + 7] = 0; + c = ~sum16(pkt + ihl, seglen, pseudo(17, seglen)); + if (c == 0) c = 0xffff; /* UDP: 0 means "none" */ + pkt[ihl + 6] = (unsigned char)(c >> 8); pkt[ihl + 7] = (unsigned char)c; + ip_send(ihl, len); + } } } diff --git a/tools/gateway.py b/tools/gateway.py index 590526e..f5fc701 100644 --- a/tools/gateway.py +++ b/tools/gateway.py @@ -126,9 +126,19 @@ def icmp_echo(seq, payload=b"gbos-ping-0123456789"): ip = ip[:10] + struct.pack("!H", inet_cksum(ip)) + ip[12:] return ip + icmp +def udp_packet(sport, dport, payload): + ulen = 8 + len(payload) + udp = struct.pack("!HHHH", sport, dport, ulen, 0) + payload + pseudo = GW_IP + GB_IP + bytes([0, 17]) + struct.pack("!H", ulen) + ck = inet_cksum(pseudo + udp) or 0xffff + udp = udp[:6] + struct.pack("!H", ck) + udp[8:] + ip = struct.pack("!BBHHHBBH", 0x45, 0, 20+ulen, 7, 0, 64, 17, 0) + GW_IP + GB_IP + ip = ip[:10] + struct.pack("!H", inet_cksum(ip)) + ip[12:] + return ip + udp + def main(): ap = argparse.ArgumentParser() - ap.add_argument("--mode", default="echo", choices=["echo", "http", "chat", "irc", "ping"]) + ap.add_argument("--mode", default="echo", choices=["echo", "http", "chat", "irc", "ping", "udp"]) ap.add_argument("--cmd", default="necho") ap.add_argument("--nick", default="gameboy") ap.add_argument("--channel", default="#sl0p") @@ -159,6 +169,17 @@ def main(): m = bytes(payload).decode("latin1", "replace") sys.stderr.write("\n[gw] GB says: %s\n" % m) return [("<bot> " + m).encode()] + elif a.mode == "udp": + def on_frame(payload): + p = bytes(payload) + if len(p) >= 28 and p[9] == 17: + ihl = (p[0] & 0x0f) * 4 + sport, dport, ulen = struct.unpack("!HHH", p[ihl:ihl+6]) + data = p[ihl+8:ihl+8+ulen-8] + ck_ok = inet_cksum(GB_IP + GW_IP + bytes([0,17]) + p[ihl+4:ihl+6] + p[ihl:]) == 0 + sys.stderr.write("\n[gw] UDP echo %d->%d: %r cksum=%s\n" + % (sport, dport, data, "ok" if ck_ok else "BAD")) + return [] elif a.mode == "ping": def on_frame(payload): p = bytes(payload) @@ -183,6 +204,11 @@ def main(): except Exception: pass irc_holder[0] = IRC(a.host, a.port, a.nick, a.channel, to_gb) threading.Thread(target=irc_holder[0].loop, daemon=True).start() + if a.mode == "udp": + time.sleep(1.0) + p.stdin.write(slip_encode(udp_packet(5000, 7, b"hello udp gbos"))); p.stdin.flush() + sys.stderr.write("[gw] sent UDP :5000->:7 'hello udp gbos'\n") + time.sleep(2.0) if a.mode == "ping": time.sleep(1.0) for seq in range(1, 5): |