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udhcpc: filter unwanted packets in kernel

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(Cristian Ionescu-Idbohrn <cristian.ionescu-idbohrn@axis.com>)
This commit is contained in:
Denis Vlasenko 2008-01-25 22:46:34 +00:00
parent 893988182a
commit b76b9a4328
5 changed files with 64 additions and 10 deletions
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55
networking/udhcp/clientsocket.c
View File

@ -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;
}

7
networking/udhcp/common.h
View File

@ -14,6 +14,9 @@
#define DEFAULT_SCRIPT "/usr/share/udhcpc/default.script"
#define SERVER_PORT 67
#define CLIENT_PORT 68
extern const uint8_t MAC_BCAST_ADDR[6]; /* six all-ones */
/*** packet.h ***/
@ -21,7 +24,7 @@ extern const uint8_t MAC_BCAST_ADDR[6]; /* six all-ones */
#include <netinet/udp.h>
#include <netinet/ip.h>
#define DHCP_OPTIONS_BUFSIZE 308
#define DHCP_OPTIONS_BUFSIZE 308
struct dhcpMessage {
uint8_t op;
@ -93,7 +96,7 @@ int listen_socket(/*uint32_t ip,*/ int port, const char *inf);
int arpping(uint32_t test_ip, uint32_t from_ip, uint8_t *from_mac, const char *interface);
#if ENABLE_FEATURE_UDHCP_DEBUG
# define DEBUG(str, args...) bb_info_msg(str, ## args)
# define DEBUG(str, args...) bb_info_msg("### " str, ## args)
#else
# define DEBUG(str, args...) do {;} while (0)
#endif

3
networking/udhcp/dhcpc.c
View File

@ -452,7 +452,8 @@ int udhcpc_main(int argc, char **argv)
if (listen_mode == LISTEN_KERNEL)
len = udhcp_recv_packet(&packet, sockfd);
else len = get_raw_packet(&packet, sockfd);
else
len = get_raw_packet(&packet, sockfd);
if (len == -1) { /* error is severe, reopen socket */
DEBUG("error on read, %s, reopening socket", strerror(errno));

6
networking/udhcp/dhcprelay.c
View File

@ -155,12 +155,12 @@ static int init_sockets(char **client, int num_clients,
int i, n;
/* talk to real server on bootps */
fds[0] = listen_socket(/*INADDR_ANY,*/ 67, server);
fds[0] = listen_socket(/*INADDR_ANY,*/ SERVER_PORT, server);
n = fds[0];
for (i = 1; i < num_clients; i++) {
/* listen for clients on bootps */
fds[i] = listen_socket(/*INADDR_ANY,*/ 67, client[i-1]);
fds[i] = listen_socket(/*INADDR_ANY,*/ SERVER_PORT, client[i-1]);
if (fds[i] > n)
n = fds[i];
}
@ -289,7 +289,7 @@ int dhcprelay_main(int argc, char **argv)
struct sockaddr_in server_addr;
server_addr.sin_family = AF_INET;
server_addr.sin_port = htons(67);
server_addr.sin_port = htons(SERVER_PORT);
if (argc == 4) {
if (!inet_aton(argv[3], &server_addr.sin_addr))
bb_perror_msg_and_die("didn't grok server");

3
networking/udhcp/options.h
View File

@ -28,9 +28,6 @@ enum {
/*****************************************************************/
/* DHCP protocol -- see RFC 2131 */
#define SERVER_PORT 67
#define CLIENT_PORT 68
#define DHCP_MAGIC 0x63825363