pcap-linux.c

Ubuntu packages of security software。 相当不错的源码

	int		arptype;
	struct ifreq	ifr;

	do {
		/* Open the socket */

		handle->fd = socket(PF_INET, SOCK_PACKET, htons(ETH_P_ALL));
		if (handle->fd == -1) {
			snprintf(ebuf, PCAP_ERRBUF_SIZE,
				 "socket: %s", pcap_strerror(errno));
			break;
		}

		/* It worked - we are using the old interface */
		handle->md.sock_packet = 1;

		/* ...which means we get the link-layer header. */
		handle->md.cooked = 0;

		/* Bind to the given device */

		if (!device) {
		        strncpy(ebuf, "pcap_open_live: The \"any\" device isn't supported on 2.0[.x]-kernel systems",
				PCAP_ERRBUF_SIZE);
			break;
		}
		if (iface_bind_old(handle->fd, device, ebuf) == -1)
			break;

		/*
		 * Try to get the link-layer type.
		 */
		arptype = iface_get_arptype(handle->fd, device, ebuf);
		if (arptype == -1)
			break;

		/*
		 * Try to find the DLT_ type corresponding to that
		 * link-layer type.
		 */
		map_arphrd_to_dlt(handle, arptype, 0);
		if (handle->linktype == -1) {
			snprintf(ebuf, PCAP_ERRBUF_SIZE,
				 "unknown arptype %d", arptype);
			break;
		}

		/* Go to promisc mode if requested */

		if (promisc) {
			memset(&ifr, 0, sizeof(ifr));
			strncpy(ifr.ifr_name, device, sizeof(ifr.ifr_name));
			if (ioctl(handle->fd, SIOCGIFFLAGS, &ifr) == -1) {
				snprintf(ebuf, PCAP_ERRBUF_SIZE,
					 "SIOCGIFFLAGS: %s", pcap_strerror(errno));
				break;
			}
			if ((ifr.ifr_flags & IFF_PROMISC) == 0) {
				/*
				 * Promiscuous mode isn't currently on,
				 * so turn it on, and remember that
				 * we should turn it off when the
				 * pcap_t is closed.
				 */

				/*
				 * If we haven't already done so, arrange
				 * to have "pcap_close_all()" called when
				 * we exit.
				 */
				if (!did_atexit) {
					if (atexit(pcap_close_all) == -1) {
						/*
						 * "atexit()" failed; don't
						 * put the interface in
						 * promiscuous mode, just
						 * give up.
						 */
						strncpy(ebuf, "atexit failed",
							PCAP_ERRBUF_SIZE);
						break;
					}
					did_atexit = 1;
				}

				ifr.ifr_flags |= IFF_PROMISC;
				if (ioctl(handle->fd, SIOCSIFFLAGS, &ifr) == -1) {
				        snprintf(ebuf, PCAP_ERRBUF_SIZE,
						 "SIOCSIFFLAGS: %s",
						 pcap_strerror(errno));
					break;
				}
				handle->md.clear_promisc = 1;

				/*
				 * Add this to the list of pcaps
				 * to close when we exit.
				 */
				handle->md.next = pcaps_to_close;
				pcaps_to_close = handle;
			}
		}

		/*
		 * Default value for offset to align link-layer payload
		 * on a 4-byte boundary.
		 */
		handle->offset	 = 0;

		return 1;

	} while (0);

	pcap_close_linux(handle);
	return 0;
}

/*
 *  Bind the socket associated with FD to the given device using the
 *  interface of the old kernels.
 */
static int
iface_bind_old(int fd, const char *device, char *ebuf)
{
	struct sockaddr	saddr;
	int		err;
	socklen_t	errlen = sizeof(err);

	memset(&saddr, 0, sizeof(saddr));
	strncpy(saddr.sa_data, device, sizeof(saddr.sa_data));
	if (bind(fd, &saddr, sizeof(saddr)) == -1) {
		snprintf(ebuf, PCAP_ERRBUF_SIZE,
			 "bind: %s", pcap_strerror(errno));
		return -1;
	}

	/* Any pending errors, e.g., network is down? */

	if (getsockopt(fd, SOL_SOCKET, SO_ERROR, &err, &errlen) == -1) {
		snprintf(ebuf, PCAP_ERRBUF_SIZE,
			"getsockopt: %s", pcap_strerror(errno));
		return -1;
	}

	if (err > 0) {
		snprintf(ebuf, PCAP_ERRBUF_SIZE,
			"bind: %s", pcap_strerror(err));
		return -1;
	}

	return 0;
}


/* ===== System calls available on all supported kernels ============== */

/*
 *  Query the kernel for the MTU of the given interface.
 */
static int
iface_get_mtu(int fd, const char *device, char *ebuf)
{
	struct ifreq	ifr;

	if (!device)
		return BIGGER_THAN_ALL_MTUS;

	memset(&ifr, 0, sizeof(ifr));
	strncpy(ifr.ifr_name, device, sizeof(ifr.ifr_name));

	if (ioctl(fd, SIOCGIFMTU, &ifr) == -1) {
		snprintf(ebuf, PCAP_ERRBUF_SIZE,
			 "SIOCGIFMTU: %s", pcap_strerror(errno));
		return -1;
	}

	return ifr.ifr_mtu;
}

/*
 *  Get the hardware type of the given interface as ARPHRD_xxx constant.
 */
static int
iface_get_arptype(int fd, const char *device, char *ebuf)
{
	struct ifreq	ifr;

	memset(&ifr, 0, sizeof(ifr));
	strncpy(ifr.ifr_name, device, sizeof(ifr.ifr_name));

	if (ioctl(fd, SIOCGIFHWADDR, &ifr) == -1) {
		snprintf(ebuf, PCAP_ERRBUF_SIZE,
			 "SIOCGIFHWADDR: %s", pcap_strerror(errno));
		return -1;
	}

	return ifr.ifr_hwaddr.sa_family;
}

#ifdef SO_ATTACH_FILTER
static int
fix_program(pcap_t *handle, struct sock_fprog *fcode)
{
	size_t prog_size;
	register int i;
	register struct bpf_insn *p;
	struct bpf_insn *f;
	int len;

	/*
	 * Make a copy of the filter, and modify that copy if
	 * necessary.
	 */
	prog_size = sizeof(*handle->fcode.bf_insns) * handle->fcode.bf_len;
	len = handle->fcode.bf_len;
	f = (struct bpf_insn *)malloc(prog_size);
	if (f == NULL) {
		snprintf(handle->errbuf, sizeof(handle->errbuf),
			 "malloc: %s", pcap_strerror(errno));
		return -1;
	}
	memcpy(f, handle->fcode.bf_insns, prog_size);
	fcode->len = len;
	fcode->filter = (struct sock_filter *) f;

	for (i = 0; i < len; ++i) {
		p = &f[i];
		/*
		 * What type of instruction is this?
		 */
		switch (BPF_CLASS(p->code)) {

		case BPF_RET:
			/*
			 * It's a return instruction; is the snapshot
			 * length a constant, rather than the contents
			 * of the accumulator?
			 */
			if (BPF_MODE(p->code) == BPF_K) {
				/*
				 * Yes - if the value to be returned,
				 * i.e. the snapshot length, is anything
				 * other than 0, make it 65535, so that
				 * the packet is truncated by "recvfrom()",
				 * not by the filter.
				 *
				 * XXX - there's nothing we can easily do
				 * if it's getting the value from the
				 * accumulator; we'd have to insert
				 * code to force non-zero values to be
				 * 65535.
				 */
				if (p->k != 0)
					p->k = 65535;
			}
			break;

		case BPF_LD:
		case BPF_LDX:
			/*
			 * It's a load instruction; is it loading
			 * from the packet?
			 */
			switch (BPF_MODE(p->code)) {

			case BPF_ABS:
			case BPF_IND:
			case BPF_MSH:
				/*
				 * Yes; are we in cooked mode?
				 */
				if (handle->md.cooked) {
					/*
					 * Yes, so we need to fix this
					 * instruction.
					 */
					if (fix_offset(p) < 0) {
						/*
						 * We failed to do so.
						 * Return 0, so our caller
						 * knows to punt to userland.
						 */
						return 0;
					}
				}
				break;
			}
			break;
		}
	}
	return 1;	/* we succeeded */
}

static int
fix_offset(struct bpf_insn *p)
{
	/*
	 * What's the offset?
	 */
	if (p->k >= SLL_HDR_LEN) {
		/*
		 * It's within the link-layer payload; that starts at an
		 * offset of 0, as far as the kernel packet filter is
		 * concerned, so subtract the length of the link-layer
		 * header.
		 */
		p->k -= SLL_HDR_LEN;
	} else if (p->k == 14) {
		/*
		 * It's the protocol field; map it to the special magic
		 * kernel offset for that field.
		 */
		p->k = SKF_AD_OFF + SKF_AD_PROTOCOL;
	} else {
		/*
		 * It's within the header, but it's not one of those
		 * fields; we can't do that in the kernel, so punt
		 * to userland.
		 */
		return -1;
	}
	return 0;
}

static int
set_kernel_filter(pcap_t *handle, struct sock_fprog *fcode)
{
	int total_filter_on = 0;
	int save_mode;
	int ret;
	int save_errno;

	/*
	 * The socket filter code doesn't discard all packets queued
	 * up on the socket when the filter is changed; this means
	 * that packets that don't match the new filter may show up
	 * after the new filter is put onto the socket, if those
	 * packets haven't yet been read.
	 *
	 * This means, for example, that if you do a tcpdump capture
	 * with a filter, the first few packets in the capture might
	 * be packets that wouldn't have passed the filter.
	 *
	 * We therefore discard all packets queued up on the socket
	 * when setting a kernel filter.  (This isn't an issue for
	 * userland filters, as the userland filtering is done after
	 * packets are queued up.)
	 *
	 * To flush those packets, we put the socket in read-only mode,
	 * and read packets from the socket until there are no more to
	 * read.
	 *
	 * In order to keep that from being an infinite loop - i.e.,
	 * to keep more packets from arriving while we're draining
	 * the queue - we put the "total filter", which is a filter
	 * that rejects all packets, onto the socket before draining
	 * the queue.
	 *
	 * This code deliberately ignores any errors, so that you may
	 * get bogus packets if an error occurs, rather than having
	 * the filtering done in userland even if it could have been
	 * done in the kernel.
	 */
	if (setsockopt(handle->fd, SOL_SOCKET, SO_ATTACH_FILTER,
		       &total_fcode, sizeof(total_fcode)) == 0) {
		char drain[1];

		/*
		 * Note that we've put the total filter onto the socket.
		 */
		total_filter_on = 1;

		/*
		 * Save the socket's current mode, and put it in
		 * non-blocking mode; we drain it by reading packets
		 * until we get an error (which is normally a
		 * "nothing more to be read" error).
		 */
		save_mode = fcntl(handle->fd, F_GETFL, 0);
		if (save_mode != -1 &&
		    fcntl(handle->fd, F_SETFL, save_mode | O_NONBLOCK) >= 0) {
			while (recv(handle->fd, &drain, sizeof drain,
			       MSG_TRUNC) >= 0)
				;
			save_errno = errno;
			fcntl(handle->fd, F_SETFL, save_mode);
			if (save_errno != EAGAIN) {
				/* Fatal error */
				reset_kernel_filter(handle);
				snprintf(handle->errbuf, sizeof(handle->errbuf),
				 "recv: %s", pcap_strerror(save_errno));
				return -2;
			}
		}
	}

	/*
	 * Now attach the new filter.
	 */
	ret = setsockopt(handle->fd, SOL_SOCKET, SO_ATTACH_FILTER,
			 fcode, sizeof(*fcode));
	if (ret == -1 && total_filter_on) {
		/*
		 * Well, we couldn't set that filter on the socket,
		 * but we could set the total filter on the socket.
		 *
		 * This could, for example, mean that the filter was
		 * too big to put into the kernel, so we'll have to
		 * filter in userland; in any case, we'll be doing
		 * filtering in userland, so we need to remove the
		 * total filter so we see packets.
		 */
		save_errno = errno;

		/*
		 * XXX - if this fails, we're really screwed;
		 * we have the total filter on the socket,
		 * and it won't come off.  What do we do then?
		 */
		reset_kernel_filter(handle);

		errno = save_errno;
	}
	return ret;
}

static int
reset_kernel_filter(pcap_t *handle)
{
	/*
	 * setsockopt() barfs unless it get a dummy parameter.
	 * valgrind whines unless the value is initialized,
	 * as it has no idea that setsockopt() ignores its
	 * parameter.
	 */
	int dummy = 0;

	return setsockopt(handle->fd, SOL_SOCKET, SO_DETACH_FILTER,
				   &dummy, sizeof(dummy));
}
#endif