diff options
Diffstat (limited to 'networking/udhcp/clientsocket.c')
| -rw-r--r-- | networking/udhcp/clientsocket.c | 55 |
1 files changed, 54 insertions, 1 deletions
diff --git a/networking/udhcp/clientsocket.c b/networking/udhcp/clientsocket.c index 541f883..954db53 100644 --- a/networking/udhcp/clientsocket.c +++ b/networking/udhcp/clientsocket.c @@ -30,22 +30,75 @@ #include <linux/if_packet.h> #include <linux/if_ether.h> #endif +#include <linux/filter.h> #include "common.h" +#define SERVER_AND_CLIENT_PORTS ((SERVER_PORT << 16) + CLIENT_PORT) int raw_socket(int ifindex) { int fd; struct sockaddr_ll sock; - DEBUG("Opening raw socket on ifindex %d", ifindex); + /* + * Comment: + * + * I've selected not to see LL header, so BPF doesn't see it, too. + * The filter may also pass non-IP and non-ARP packets, but we do + * a more complete check when receiving the message in userspace. + * + * and filter shamelessly stolen from: + * + * http://www.flamewarmaster.de/software/dhcpclient/ + * + * There are a few other interesting ideas on that page (look under + * "Motivation"). Use of netlink events is most interesting. Think + * of various network servers listening for events and reconfiguring. + * That would obsolete sending HUP signals and/or make use of restarts. + * + * Copyright: 2006, 2007 Stefan Rompf <sux@loplof.de>. + * License: GPL v2. + * + * TODO: make conditional? + */ + static const struct sock_filter filter_instr[] = { + /* check for udp */ + 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, ~0UL), /* L3: pass */ + BPF_STMT(BPF_RET|BPF_K, 0), /* L4: reject */ + }; + static const struct sock_fprog filter_prog = { + .len = sizeof(filter_instr) / sizeof(filter_instr[0]), + /* casting const away: */ + .filter = (struct sock_filter *) filter_instr, + }; + + DEBUG("opening raw socket on ifindex %d", ifindex); + fd = xsocket(PF_PACKET, SOCK_DGRAM, htons(ETH_P_IP)); + DEBUG("got raw socket fd %d", fd); + + /* Ignoring error (kernel may lack support for this) */ + if (setsockopt(fd, SOL_SOCKET, SO_ATTACH_FILTER, &filter_prog, + sizeof(filter_prog)) >= 0) + DEBUG("attached filter to raw socket fd %d", fd); sock.sll_family = AF_PACKET; sock.sll_protocol = htons(ETH_P_IP); sock.sll_ifindex = ifindex; xbind(fd, (struct sockaddr *) &sock, sizeof(sock)); + DEBUG("bound to raw socket fd %d", fd); return fd; } |