diff options
| -rw-r--r-- | networking/udhcp/dhcpc.c | 44 |
1 files changed, 24 insertions, 20 deletions
diff --git a/networking/udhcp/dhcpc.c b/networking/udhcp/dhcpc.c index 7e5ab61..d97a404 100644 --- a/networking/udhcp/dhcpc.c +++ b/networking/udhcp/dhcpc.c @@ -714,22 +714,25 @@ static int udhcp_raw_socket(int ifindex) * * TODO: make conditional? */ -#define SERVER_AND_CLIENT_PORTS ((67 << 16) + 68) static const struct sock_filter filter_instr[] = { - /* check for udp */ + /* load 9th byte (protocol) */ BPF_STMT(BPF_LD|BPF_B|BPF_ABS, 9), - BPF_JUMP(BPF_JMP|BPF_JEQ|BPF_K, IPPROTO_UDP, 2, 0), /* L5, L1, is UDP? */ - /* ugly check for arp on ethernet-like and IPv4 */ - BPF_STMT(BPF_LD|BPF_W|BPF_ABS, 2), /* L1: */ - BPF_JUMP(BPF_JMP|BPF_JEQ|BPF_K, 0x08000604, 3, 4), /* L3, L4 */ - /* skip IP header */ - BPF_STMT(BPF_LDX|BPF_B|BPF_MSH, 0), /* L5: */ - /* check udp source and destination ports */ - BPF_STMT(BPF_LD|BPF_W|BPF_IND, 0), - BPF_JUMP(BPF_JMP|BPF_JEQ|BPF_K, SERVER_AND_CLIENT_PORTS, 0, 1), /* L3, L4 */ - /* returns */ - BPF_STMT(BPF_RET|BPF_K, 0x0fffffff ), /* L3: pass */ - BPF_STMT(BPF_RET|BPF_K, 0), /* L4: reject */ + /* jump to L1 if it is IPPROTO_UDP, else to L4 */ + BPF_JUMP(BPF_JMP|BPF_JEQ|BPF_K, IPPROTO_UDP, 0, 6), + /* L1: load halfword from offset 6 (flags and frag offset) */ + BPF_STMT(BPF_LD|BPF_H|BPF_ABS, 6), + /* jump to L4 if any bits in frag offset field are set, else to L2 */ + BPF_JUMP(BPF_JMP|BPF_JSET|BPF_K, 0x1fff, 4, 0), + /* L2: skip IP header (load index reg with header len) */ + BPF_STMT(BPF_LDX|BPF_B|BPF_MSH, 0), + /* load udp destination port from halfword[header_len + 2] */ + BPF_STMT(BPF_LD|BPF_H|BPF_IND, 2), + /* jump to L3 if udp dport is CLIENT_PORT, else to L4 */ + BPF_JUMP(BPF_JMP|BPF_JEQ|BPF_K, 68, 0, 1), + /* L3: accept packet */ + BPF_STMT(BPF_RET|BPF_K, 0xffffffff), + /* L4: discard packet */ + BPF_STMT(BPF_RET|BPF_K, 0), }; static const struct sock_fprog filter_prog = { .len = sizeof(filter_instr) / sizeof(filter_instr[0]), @@ -742,18 +745,19 @@ static int udhcp_raw_socket(int ifindex) fd = xsocket(PF_PACKET, SOCK_DGRAM, htons(ETH_P_IP)); log1("Got raw socket fd %d", fd); //log2? - if (SERVER_PORT == 67 && CLIENT_PORT == 68) { - /* Use only if standard ports are in use */ + sock.sll_family = AF_PACKET; + sock.sll_protocol = htons(ETH_P_IP); + sock.sll_ifindex = ifindex; + xbind(fd, (struct sockaddr *) &sock, sizeof(sock)); + + if (CLIENT_PORT == 68) { + /* Use only if standard port is in use */ /* Ignoring error (kernel may lack support for this) */ if (setsockopt(fd, SOL_SOCKET, SO_ATTACH_FILTER, &filter_prog, sizeof(filter_prog)) >= 0) log1("Attached filter to raw socket fd %d", fd); // log? } - sock.sll_family = AF_PACKET; - sock.sll_protocol = htons(ETH_P_IP); - sock.sll_ifindex = ifindex; - xbind(fd, (struct sockaddr *) &sock, sizeof(sock)); log1("Created raw socket"); return fd; |