713e6d78e
Vladislav Grishenko
2011-02-14
Subject
udhcpc: use more correct, and more importantly, more understandable BPF code
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networking/udhcp/dhcpc.c+24 -20
| @@ -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; | |