pcap-linux.c

用来监视网络通信数据的源代码和应用程序,方便网络程序底层开发.

#ifndef ARPHRD_FDDI	/* From Linux 2.2.13 */
#define ARPHRD_FDDI	774
#endif
	case ARPHRD_FDDI:
		handle->linktype = DLT_FDDI;
		handle->offset = 3;
		break;

#ifndef ARPHRD_ATM  /* FIXME: How to #include this? */
#define ARPHRD_ATM 19
#endif
	case ARPHRD_ATM:
		/*
		 * The Classical IP implementation in ATM for Linux
		 * supports both what RFC 1483 calls "LLC Encapsulation",
		 * in which each packet has an LLC header, possibly
		 * with a SNAP header as well, prepended to it, and
		 * what RFC 1483 calls "VC Based Multiplexing", in which
		 * different virtual circuits carry different network
		 * layer protocols, and no header is prepended to packets.
		 *
		 * They both have an ARPHRD_ type of ARPHRD_ATM, so
		 * you can't use the ARPHRD_ type to find out whether
		 * captured packets will have an LLC header, and,
		 * while there's a socket ioctl to *set* the encapsulation
		 * type, there's no ioctl to *get* the encapsulation type.
		 *
		 * This means that
		 *
		 *	programs that dissect Linux Classical IP frames
		 *	would have to check for an LLC header and,
		 *	depending on whether they see one or not, dissect
		 *	the frame as LLC-encapsulated or as raw IP (I
		 *	don't know whether there's any traffic other than
		 *	IP that would show up on the socket, or whether
		 *	there's any support for IPv6 in the Linux
		 *	Classical IP code);
		 *
		 *	filter expressions would have to compile into
		 *	code that checks for an LLC header and does
		 *	the right thing.
		 *
		 * Both of those are a nuisance - and, at least on systems
		 * that support PF_PACKET sockets, we don't have to put
		 * up with those nuisances; instead, we can just capture
		 * in cooked mode.  That's what we'll do, if we can.
		 * Otherwise, we'll just fail.
		 */
		if (cooked_ok)
			handle->linktype = DLT_LINUX_SLL;
		else
			handle->linktype = -1;
		break;

#ifndef ARPHRD_IEEE80211  /* From Linux 2.4.6 */
#define ARPHRD_IEEE80211 801
#endif
	case ARPHRD_IEEE80211:
		handle->linktype = DLT_IEEE802_11;
		break;

#ifndef ARPHRD_IEEE80211_PRISM  /* From Linux 2.4.18 */
#define ARPHRD_IEEE80211_PRISM 802
#endif
	case ARPHRD_IEEE80211_PRISM:
		handle->linktype = DLT_PRISM_HEADER;
		break;

	case ARPHRD_PPP:
		/*
		 * Some PPP code in the kernel supplies no link-layer
		 * header whatsoever to PF_PACKET sockets; other PPP
		 * code supplies PPP link-layer headers ("syncppp.c");
		 * some PPP code might supply random link-layer
		 * headers (PPP over ISDN - there's code in Ethereal,
		 * for example, to cope with PPP-over-ISDN captures
		 * with which the Ethereal developers have had to cope,
		 * heuristically trying to determine which of the
		 * oddball link-layer headers particular packets have).
		 *
		 * As such, we just punt, and run all PPP interfaces
		 * in cooked mode, if we can; otherwise, we just treat
		 * it as DLT_RAW, for now - if somebody needs to capture,
		 * on a 2.0[.x] kernel, on PPP devices that supply a
		 * link-layer header, they'll have to add code here to
		 * map to the appropriate DLT_ type (possibly adding a
		 * new DLT_ type, if necessary).
		 */
		if (cooked_ok)
			handle->linktype = DLT_LINUX_SLL;
		else {
			/*
			 * XXX - handle ISDN types here?  We can't fall
			 * back on cooked sockets, so we'd have to
			 * figure out from the device name what type of
			 * link-layer encapsulation it's using, and map
			 * that to an appropriate DLT_ value, meaning
			 * we'd map "isdnN" devices to DLT_RAW (they
			 * supply raw IP packets with no link-layer
			 * header) and "isdY" devices to a new DLT_I4L_IP
			 * type that has only an Ethernet packet type as
			 * a link-layer header.
			 *
			 * But sometimes we seem to get random crap
			 * in the link-layer header when capturing on
			 * ISDN devices....
			 */
			handle->linktype = DLT_RAW;
		}
		break;

#ifndef ARPHRD_CISCO
#define ARPHRD_CISCO 513 /* previously ARPHRD_HDLC */
#endif
	case ARPHRD_CISCO:
		handle->linktype = DLT_C_HDLC;
		break;

	/* Not sure if this is correct for all tunnels, but it
	 * works for CIPE */
	case ARPHRD_TUNNEL:
#ifndef ARPHRD_SIT
#define ARPHRD_SIT 776	/* From Linux 2.2.13 */
#endif
	case ARPHRD_SIT:
	case ARPHRD_CSLIP:
	case ARPHRD_SLIP6:
	case ARPHRD_CSLIP6:
	case ARPHRD_ADAPT:
	case ARPHRD_SLIP:
#ifndef ARPHRD_RAWHDLC
#define ARPHRD_RAWHDLC 518
#endif
	case ARPHRD_RAWHDLC:
#ifndef ARPHRD_DLCI
#define ARPHRD_DLCI 15
#endif
	case ARPHRD_DLCI:
		/*
		 * XXX - should some of those be mapped to DLT_LINUX_SLL
		 * instead?  Should we just map all of them to DLT_LINUX_SLL?
		 */
		handle->linktype = DLT_RAW;
		break;

#ifndef ARPHRD_FRAD
#define ARPHRD_FRAD 770
#endif
	case ARPHRD_FRAD:
		handle->linktype = DLT_FRELAY;
		break;

	case ARPHRD_LOCALTLK:
		handle->linktype = DLT_LTALK;
		break;

#ifndef ARPHRD_FCPP
#define ARPHRD_FCPP	784
#endif
	case ARPHRD_FCPP:
#ifndef ARPHRD_FCAL
#define ARPHRD_FCAL	785
#endif
	case ARPHRD_FCAL:
#ifndef ARPHRD_FCPL
#define ARPHRD_FCPL	786
#endif
	case ARPHRD_FCPL:
#ifndef ARPHRD_FCFABRIC
#define ARPHRD_FCFABRIC	787
#endif
	case ARPHRD_FCFABRIC:
		/*
		 * We assume that those all mean RFC 2625 IP-over-
		 * Fibre Channel, with the RFC 2625 header at
		 * the beginning of the packet.
		 */
		handle->linktype = DLT_IP_OVER_FC;
		break;

#ifndef ARPHRD_IRDA
#define ARPHRD_IRDA	783
#endif
	case ARPHRD_IRDA:
		/* Don't expect IP packet out of this interfaces... */
		handle->linktype = DLT_LINUX_IRDA;
		/* We need to save packet direction for IrDA decoding,
		 * so let's use "Linux-cooked" mode. Jean II */
		//handle->md.cooked = 1;
		break;

	default:
		handle->linktype = -1;
		break;
	}
}

/* ===== Functions to interface to the newer kernels ================== */

/*
 *  Try to open a packet socket using the new kernel interface.
 *  Returns 0 on failure.
 *  FIXME: 0 uses to mean success (Sebastian)
 */
static int
live_open_new(pcap_t *handle, const char *device, int promisc,
	      int to_ms, char *ebuf)
{
#ifdef HAVE_PF_PACKET_SOCKETS
	int			sock_fd = -1, device_id, arptype;
	int			err;
	int			fatal_err = 0;
	struct packet_mreq	mr;

	/* One shot loop used for error handling - bail out with break */

	do {
		/*
		 * Open a socket with protocol family packet. If a device is
		 * given we try to open it in raw mode otherwise we use
		 * the cooked interface.
		 */
		sock_fd = device ?
			socket(PF_PACKET, SOCK_RAW, htons(ETH_P_ALL))
		      : socket(PF_PACKET, SOCK_DGRAM, htons(ETH_P_ALL));

		if (sock_fd == -1) {
			snprintf(ebuf, PCAP_ERRBUF_SIZE, "socket: %s",
				 pcap_strerror(errno) );
			break;
		}

		/* It seems the kernel supports the new interface. */
		handle->md.sock_packet = 0;

		/*
		 * Get the interface index of the loopback device.
		 * If the attempt fails, don't fail, just set the
		 * "md.lo_ifindex" to -1.
		 *
		 * XXX - can there be more than one device that loops
		 * packets back, i.e. devices other than "lo"?  If so,
		 * we'd need to find them all, and have an array of
		 * indices for them, and check all of them in
		 * "pcap_read_packet()".
		 */
		handle->md.lo_ifindex = iface_get_id(sock_fd, "lo", ebuf);

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

		/*
		 * What kind of frames do we have to deal with? Fall back
		 * to cooked mode if we have an unknown interface type.
		 */

		if (device) {
			/* Assume for now we don't need cooked mode. */
			handle->md.cooked = 0;

			arptype	= iface_get_arptype(sock_fd, device, ebuf);
			if (arptype == -1) {
				fatal_err = 1;
				break;
			}
			map_arphrd_to_dlt(handle, arptype, 1);
			if (handle->linktype == -1 ||
			    handle->linktype == DLT_LINUX_SLL ||
			    handle->linktype == DLT_LINUX_IRDA ||
			    (handle->linktype == DLT_EN10MB &&
			     (strncmp("isdn", device, 4) == 0 ||
			      strncmp("isdY", device, 4) == 0))) {
				/*
				 * Unknown interface type (-1), or a
				 * device we explicitly chose to run
				 * in cooked mode (e.g., PPP devices),
				 * or an ISDN device (whose link-layer
				 * type we can only determine by using
				 * APIs that may be different on different
				 * kernels) - reopen in cooked mode.
				 */
				if (close(sock_fd) == -1) {
					snprintf(ebuf, PCAP_ERRBUF_SIZE,
						 "close: %s", pcap_strerror(errno));
					break;
				}
				sock_fd = socket(PF_PACKET, SOCK_DGRAM,
						 htons(ETH_P_ALL));
				if (sock_fd == -1) {
					snprintf(ebuf, PCAP_ERRBUF_SIZE,
						 "socket: %s", pcap_strerror(errno));
					break;
				}
				handle->md.cooked = 1;

				if (handle->linktype == -1) {
					/*
					 * Warn that we're falling back on
					 * cooked mode; we may want to
					 * update "map_arphrd_to_dlt()"
					 * to handle the new type.
					 */
					snprintf(ebuf, PCAP_ERRBUF_SIZE,
						"arptype %d not "
						"supported by libpcap - "
						"falling back to cooked "
						"socket",
						arptype);
				}
				/* IrDA capture is not a real "cooked" capture,
				 * it's IrLAP frames, not IP packets. */
				if(handle->linktype != DLT_LINUX_IRDA)
					handle->linktype = DLT_LINUX_SLL;
			}

			device_id = iface_get_id(sock_fd, device, ebuf);
			if (device_id == -1)
				break;

			if ((err = iface_bind(sock_fd, device_id, ebuf)) < 0) {
				if (err == -2)
					fatal_err = 1;
				break;
			}
		} else {
			/*
			 * This is cooked mode.
			 */
			handle->md.cooked = 1;
			handle->linktype = DLT_LINUX_SLL;

			/*
			 * XXX - squelch GCC complaints about
			 * uninitialized variables; if we can't
			 * select promiscuous mode on all interfaces,
			 * we should move the code below into the
			 * "if (device)" branch of the "if" and
			 * get rid of the next statement.
			 */
			device_id = -1;
		}

		/*
		 * Select promiscuous mode on if "promisc" is set.
		 *
		 * Do not turn allmulti mode on if we don't select
		 * promiscuous mode - on some devices (e.g., Orinoco
		 * wireless interfaces), allmulti mode isn't supported
		 * and the driver implements it by turning promiscuous
		 * mode on, and that screws up the operation of the
		 * card as a normal networking interface, and on no
		 * other platform I know of does starting a non-
		 * promiscuous capture affect which multicast packets
		 * are received by the interface.
		 */

		/*
		 * Hmm, how can we set promiscuous mode on all interfaces?
		 * I am not sure if that is possible at all.
		 */

		if (device && promisc) {
			memset(&mr, 0, sizeof(mr));
			mr.mr_ifindex = device_id;
			mr.mr_type    = PACKET_MR_PROMISC;
			if (setsockopt(sock_fd, SOL_PACKET,
				PACKET_ADD_MEMBERSHIP, &mr, sizeof(mr)) == -1)
			{
				snprintf(ebuf, PCAP_ERRBUF_SIZE,
					"setsockopt: %s", pcap_strerror(errno));
				break;
			}
		}

		/* Save the socket FD in the pcap structure */

		handle->fd 	 = sock_fd;

		return 1;

	} while(0);

	if (sock_fd != -1)
		close(sock_fd);

	if (fatal_err)
		return -2;
	else
		return 0;
#else
	strncpy(ebuf,
		"New packet capturing interface not supported by build "
		"environment", PCAP_ERRBUF_SIZE);
	return 0;
#endif
}

#ifdef HAVE_PF_PACKET_SOCKETS
/*
 *  Return the index of the given device name. Fill ebuf and return
 *  -1 on failure.
 */
static int
iface_get_id(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, SIOCGIFINDEX, &ifr) == -1) {
		snprintf(ebuf, PCAP_ERRBUF_SIZE,
			 "ioctl: %s", pcap_strerror(errno));
		return -1;
	}

	return ifr.ifr_ifindex;
}

/*
 *  Bind the socket associated with FD to the given device.
 */
static int
iface_bind(int fd, int ifindex, char *ebuf)
{
	struct sockaddr_ll	sll;
	int			err;
	socklen_t		errlen = sizeof(err);

	memset(&sll, 0, sizeof(sll));
	sll.sll_family		= AF_PACKET;
	sll.sll_ifindex		= ifindex;
	sll.sll_protocol	= htons(ETH_P_ALL);

	if (bind(fd, (struct sockaddr *) &sll, sizeof(sll)) == -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 -2;
	}

	if (err > 0) {
		snprintf(ebuf, PCAP_ERRBUF_SIZE,
			"bind: %s", pcap_strerror(err));
		return -2;
	}

	return 0;
}

#endif


/* ===== Functions to interface to the older kernels ================== */

/*
 * With older kernels promiscuous mode is kind of interesting because we
 * have to reset the interface before exiting. The problem can't really
 * be solved without some daemon taking care of managing usage counts.
 * If we put the interface into promiscuous mode, we set a flag indicating
 * that we must take it out of that mode when the interface is closed,
 * and, when closing the interface, if that flag is set we take it out
 * of promiscuous mode.
 */

/*
 * List of pcaps for which we turned promiscuous mode on by hand.
 * If there are any such pcaps, we arrange to call "pcap_close_all()"
 * when we exit, and have it close all of them to turn promiscuous mode
 * off.
 */
static struct pcap *pcaps_to_close;

/*
 * TRUE if we've already called "atexit()" to cause "pcap_close_all()" to
 * be called on exit.
 */
static int did_atexit;

static void	pcap_close_all(void)
{
	struct pcap *handle;

	while ((handle = pcaps_to_close) != NULL)
		pcap_close(handle);
}

static void	pcap_close_linux( pcap_t *handle )
{
	struct pcap	*p, *prevp;
	struct ifreq	ifr;

	if (handle->md.clear_promisc) {
		/*
		 * We put the interface into promiscuous mode; take
		 * it out of promiscuous mode.
		 *
		 * XXX - if somebody else wants it in promiscuous mode,
		 * this code cannot know that, so it'll take it out
		 * of promiscuous mode.  That's not fixable in 2.0[.x]