pcap-bpf.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.

		fd = open(device, O_RDONLY);
	} while (fd < 0 && errno == EBUSY);

	/*
	 * XXX better message for all minors used
	 */
	if (fd < 0)
		snprintf(errbuf, PCAP_ERRBUF_SIZE, "(no devices found) %s: %s",
		    device, pcap_strerror(errno));

	return (fd);
}

static void
pcap_close_bpf(pcap_t *p)
{
	if (p->buffer != NULL)
		free(p->buffer);
	if (p->fd >= 0)
		close(p->fd);
}

/*
 * XXX - on AIX, IBM's tcpdump (and perhaps the incompatible-with-everybody-
 * else's libpcap in AIX 5.1) appears to forcibly load the BPF driver
 * if it's not already loaded, and to create the BPF devices if they
 * don't exist.
 *
 * It'd be nice if we could do the same, although the code to do so
 * might be version-dependent, alas (the way to do it isn't necessarily
 * documented).
 */
pcap_t *
pcap_open_live(const char *device, int snaplen, int promisc, int to_ms,
    char *ebuf)
{
	int fd;
	struct ifreq ifr;
	struct bpf_version bv;
#ifdef BIOCGDLTLIST
	struct bpf_dltlist bdl;
#endif
	u_int v;
	pcap_t *p;
	struct utsname osinfo;

#ifdef HAVE_REMOTE
	/*
		Retrofit; we have to make older applications compatible with the remote capture
		So, we're calling the pcap_open_remote() from here, that is a very dirty thing.
		Obviously, we cannot exploit all the new features; for instance, we cannot
		send authentication, we cannot use a UDP data connection, and so on.
	*/

	char host[PCAP_BUF_SIZE + 1];
	char port[PCAP_BUF_SIZE + 1];
	char name[PCAP_BUF_SIZE + 1];
	int srctype;

	if (pcap_parsesrcstr(device, &srctype, host, port, name, ebuf) )
		return NULL;

	if (srctype == PCAP_SRC_IFREMOTE)
	{
		p= pcap_opensource_remote(device, NULL, ebuf);

		if (p == NULL) 
			return NULL;

		p->snapshot= snaplen;
		p->timeout= to_ms;
		p->rmt_flags= (promisc) ? PCAP_OPENFLAG_PROMISCUOUS : 0;

		return p;
	}
#endif		/* HAVE_REMOTE */

#ifdef HAVE_DAG_API
	if (strstr(device, "dag")) {
		return dag_open_live(device, snaplen, promisc, to_ms, ebuf);
	}
#endif /* HAVE_DAG_API */

#ifdef BIOCGDLTLIST
	memset(&bdl, 0, sizeof(bdl));
#endif

	p = (pcap_t *)malloc(sizeof(*p));
	if (p == NULL) {
		snprintf(ebuf, PCAP_ERRBUF_SIZE, "malloc: %s",
		    pcap_strerror(errno));
		return (NULL);
	}
	memset(p, 0, sizeof(*p));
	fd = bpf_open(p, ebuf);
	if (fd < 0)
		goto bad;

	p->fd = fd;
	p->snapshot = snaplen;

	if (ioctl(fd, BIOCVERSION, (caddr_t)&bv) < 0) {
		snprintf(ebuf, PCAP_ERRBUF_SIZE, "BIOCVERSION: %s",
		    pcap_strerror(errno));
		goto bad;
	}
	if (bv.bv_major != BPF_MAJOR_VERSION ||
	    bv.bv_minor < BPF_MINOR_VERSION) {
		snprintf(ebuf, PCAP_ERRBUF_SIZE,
		    "kernel bpf filter out of date");
		goto bad;
	}

	/*
	 * Try finding a good size for the buffer; 32768 may be too
	 * big, so keep cutting it in half until we find a size
	 * that works, or run out of sizes to try.  If the default
	 * is larger, don't make it smaller.
	 *
	 * XXX - there should be a user-accessible hook to set the
	 * initial buffer size.
	 */
	if ((ioctl(fd, BIOCGBLEN, (caddr_t)&v) < 0) || v < 32768)
		v = 32768;
	for ( ; v != 0; v >>= 1) {
		/* Ignore the return value - this is because the call fails
		 * on BPF systems that don't have kernel malloc.  And if
		 * the call fails, it's no big deal, we just continue to
		 * use the standard buffer size.
		 */
		(void) ioctl(fd, BIOCSBLEN, (caddr_t)&v);

		(void)strncpy(ifr.ifr_name, device, sizeof(ifr.ifr_name));
		if (ioctl(fd, BIOCSETIF, (caddr_t)&ifr) >= 0)
			break;	/* that size worked; we're done */

		if (errno != ENOBUFS) {
			snprintf(ebuf, PCAP_ERRBUF_SIZE, "BIOCSETIF: %s: %s",
			    device, pcap_strerror(errno));
			goto bad;
		}
	}

	if (v == 0) {
		snprintf(ebuf, PCAP_ERRBUF_SIZE,
			 "BIOCSBLEN: %s: No buffer size worked", device);
		goto bad;
	}

	/* Get the data link layer type. */
	if (ioctl(fd, BIOCGDLT, (caddr_t)&v) < 0) {
		snprintf(ebuf, PCAP_ERRBUF_SIZE, "BIOCGDLT: %s",
		    pcap_strerror(errno));
		goto bad;
	}
#ifdef _AIX
	/*
	 * AIX's BPF returns IFF_ types, not DLT_ types, in BIOCGDLT.
	 */
	switch (v) {

	case IFT_ETHER:
	case IFT_ISO88023:
		v = DLT_EN10MB;
		break;

	case IFT_FDDI:
		v = DLT_FDDI;
		break;

	case IFT_ISO88025:
		v = DLT_IEEE802;
		break;

	case IFT_LOOP:
		v = DLT_NULL;
		break;

	default:
		/*
		 * We don't know what to map this to yet.
		 */
		snprintf(ebuf, PCAP_ERRBUF_SIZE, "unknown interface type %u",
		    v);
		goto bad;
	}
#endif
#if _BSDI_VERSION - 0 >= 199510
	/* The SLIP and PPP link layer header changed in BSD/OS 2.1 */
	switch (v) {

	case DLT_SLIP:
		v = DLT_SLIP_BSDOS;
		break;

	case DLT_PPP:
		v = DLT_PPP_BSDOS;
		break;

	case 11:	/*DLT_FR*/
		v = DLT_FRELAY;
		break;

	case 12:	/*DLT_C_HDLC*/
		v = DLT_CHDLC;
		break;
	}
#endif
	p->linktype = v;

#ifdef BIOCGDLTLIST
	/*
	 * We know the default link type -- now determine all the DLTs
	 * this interface supports.  If this fails with EINVAL, it's
	 * not fatal; we just don't get to use the feature later.
	 */
	if (ioctl(fd, BIOCGDLTLIST, (caddr_t)&bdl) == 0) {
		bdl.bfl_list = (u_int *) malloc(sizeof(u_int) * bdl.bfl_len);
		if (bdl.bfl_list == NULL) {
			(void)snprintf(ebuf, PCAP_ERRBUF_SIZE, "malloc: %s",
			    pcap_strerror(errno));
			goto bad;
		}

		if (ioctl(fd, BIOCGDLTLIST, (caddr_t)&bdl) < 0) {
			(void)snprintf(ebuf, PCAP_ERRBUF_SIZE,
			    "BIOCGDLTLIST: %s", pcap_strerror(errno));
			goto bad;
		}

		p->dlt_count = bdl.bfl_len;
		p->dlt_list = bdl.bfl_list;
	} else {
		if (errno != EINVAL) {
			(void)snprintf(ebuf, PCAP_ERRBUF_SIZE,
			    "BIOCGDLTLIST: %s", pcap_strerror(errno));
			goto bad;
		}
	}
#endif

	/* set timeout */
	if (to_ms != 0) {
		/*
		 * XXX - is this seconds/nanoseconds in AIX?
		 * (Treating it as such doesn't fix the timeout
		 * problem described below.)
		 */
		struct timeval to;
		to.tv_sec = to_ms / 1000;
		to.tv_usec = (to_ms * 1000) % 1000000;
		if (ioctl(p->fd, BIOCSRTIMEOUT, (caddr_t)&to) < 0) {
			snprintf(ebuf, PCAP_ERRBUF_SIZE, "BIOCSRTIMEOUT: %s",
			    pcap_strerror(errno));
			goto bad;
		}
	}

#ifdef _AIX
#ifdef	BIOCIMMEDIATE
	/*
	 * Darren Reed notes that
	 *
	 *	On AIX (4.2 at least), if BIOCIMMEDIATE is not set, the
	 *	timeout appears to be ignored and it waits until the buffer
	 *	is filled before returning.  The result of not having it
	 *	set is almost worse than useless if your BPF filter
	 *	is reducing things to only a few packets (i.e. one every
	 *	second or so).
	 *
	 * so we turn BIOCIMMEDIATE mode on if this is AIX.
	 *
	 * We don't turn it on for other platforms, as that means we
	 * get woken up for every packet, which may not be what we want;
	 * in the Winter 1993 USENIX paper on BPF, they say:
	 *
	 *	Since a process might want to look at every packet on a
	 *	network and the time between packets can be only a few
	 *	microseconds, it is not possible to do a read system call
	 *	per packet and BPF must collect the data from several
	 *	packets and return it as a unit when the monitoring
	 *	application does a read.
	 *
	 * which I infer is the reason for the timeout - it means we
	 * wait that amount of time, in the hopes that more packets
	 * will arrive and we'll get them all with one read.
	 *
	 * Setting BIOCIMMEDIATE mode on FreeBSD (and probably other
	 * BSDs) causes the timeout to be ignored.
	 *
	 * On the other hand, some platforms (e.g., Linux) don't support
	 * timeouts, they just hand stuff to you as soon as it arrives;
	 * if that doesn't cause a problem on those platforms, it may
	 * be OK to have BIOCIMMEDIATE mode on BSD as well.
	 *
	 * (Note, though, that applications may depend on the read
	 * completing, even if no packets have arrived, when the timeout
	 * expires, e.g. GUI applications that have to check for input
	 * while waiting for packets to arrive; a non-zero timeout
	 * prevents "select()" from working right on FreeBSD and
	 * possibly other BSDs, as the timer doesn't start until a
	 * "read()" is done, so the timer isn't in effect if the
	 * application is blocked on a "select()", and the "select()"
	 * doesn't get woken up for a BPF device until the buffer
	 * fills up.)
	 */
	v = 1;
	if (ioctl(p->fd, BIOCIMMEDIATE, &v) < 0) {
		snprintf(ebuf, PCAP_ERRBUF_SIZE, "BIOCIMMEDIATE: %s",
		    pcap_strerror(errno));
		goto bad;
	}
#endif	/* BIOCIMMEDIATE */
#endif	/* _AIX */

	if (promisc) {
		/* set promiscuous mode, okay if it fails */
		if (ioctl(p->fd, BIOCPROMISC, NULL) < 0) {
			snprintf(ebuf, PCAP_ERRBUF_SIZE, "BIOCPROMISC: %s",
			    pcap_strerror(errno));
		}
	}

	if (ioctl(fd, BIOCGBLEN, (caddr_t)&v) < 0) {
		snprintf(ebuf, PCAP_ERRBUF_SIZE, "BIOCGBLEN: %s",
		    pcap_strerror(errno));
		goto bad;
	}
	p->bufsize = v;
	p->buffer = (u_char *)malloc(p->bufsize);
	if (p->buffer == NULL) {
		snprintf(ebuf, PCAP_ERRBUF_SIZE, "malloc: %s",
		    pcap_strerror(errno));
		goto bad;
	}
#ifdef _AIX
	/* For some strange reason this seems to prevent the EFAULT 
	 * problems we have experienced from AIX BPF. */
	memset(p->buffer, 0x0, p->bufsize);
#endif

	/*
	 * On most BPF platforms, either you can do a "select()" or
	 * "poll()" on a BPF file descriptor and it works correctly,
	 * or you can do it and it will return "readable" if the
	 * hold buffer is full but not if the timeout expires *and*
	 * a non-blocking read will, if the hold buffer is empty
	 * but the store buffer isn't empty, rotate the buffers
	 * and return what packets are available.
	 *
	 * In the latter case, the fact that a non-blocking read
	 * will give you the available packets means you can work
	 * around the failure of "select()" and "poll()" to wake up
	 * and return "readable" when the timeout expires by using
	 * the timeout as the "select()" or "poll()" timeout, putting
	 * the BPF descriptor into non-blocking mode, and read from
	 * it regardless of whether "select()" reports it as readable
	 * or not.
	 *
	 * However, in FreeBSD 4.3 and 4.4, "select()" and "poll()"
	 * won't wake up and return "readable" if the timer expires
	 * and non-blocking reads return EWOULDBLOCK if the hold
	 * buffer is empty, even if the store buffer is non-empty.
	 *
	 * This means the workaround in question won't work.
	 *
	 * Therefore, on FreeBSD 4.3 and 4.4, we set "p->selectable_fd"
	 * to -1, which means "sorry, you can't use 'select()' or 'poll()'
	 * here".  On all other BPF platforms, we set it to the FD for
	 * the BPF device; in NetBSD, OpenBSD, and Darwin, a non-blocking
	 * read will, if the hold buffer is empty and the store buffer
	 * isn't empty, rotate the buffers and return what packets are
	 * there (and in sufficiently recent versions of OpenBSD
	 * "select()" and "poll()" should work correctly).
	 *
	 * XXX - what about AIX?
	 */
	if (uname(&osinfo) == 0) {
		/*
		 * We can check what OS this is.
		 */
		if (strcmp(osinfo.sysname, "FreeBSD") == 0 &&
		    (strncmp(osinfo.release, "4.3-", 4) == 0 ||
		     strncmp(osinfo.release, "4.4-", 4) == 0))
			p->selectable_fd = -1;
		else
			p->selectable_fd = p->fd;
	} else {
		/*
		 * We can't find out what OS this is, so assume we can
		 * do a "select()" or "poll()".
		 */
		p->selectable_fd = p->fd;
	}

	p->read_op = pcap_read_bpf;
	p->setfilter_op = pcap_setfilter_bpf;
	p->set_datalink_op = pcap_set_datalink_bpf;
	p->getnonblock_op = pcap_getnonblock_fd;
	p->setnonblock_op = pcap_setnonblock_fd;
	p->stats_op = pcap_stats_bpf;
	p->close_op = pcap_close_bpf;

	return (p);
 bad:
	(void)close(fd);
#ifdef BIOCGDLTLIST
	if (bdl.bfl_list != NULL)
		free(bdl.bfl_list);
#endif
	free(p);
	return (NULL);
}

int
pcap_platform_finddevs(pcap_if_t **alldevsp, char *errbuf)
{
#ifdef HAVE_DAG_API
	if (dag_platform_finddevs(alldevsp, errbuf) < 0)
		return (-1);
#endif /* HAVE_DAG_API */

	return (0);
}

static int
pcap_setfilter_bpf(pcap_t *p, struct bpf_program *fp)
{
	/*
	 * It looks that BPF code generated by gen_protochain() is not
	 * compatible with some of kernel BPF code (for example BSD/OS 3.1).
	 * Take a safer side for now.
	 */
	if (no_optimize) {
		/*
		 * XXX - what if we already have a filter in the kernel?
		 */
		if (install_bpf_program(p, fp) < 0)
			return (-1);
		p->md.use_bpf = 0;	/* filtering in userland */
		return (0);
	}

	/*
	 * Free any user-mode filter we might happen to have installed.
	 */
	pcap_freecode(&p->fcode);

	/*
	 * Try to install the kernel filter.
	 */
	if (ioctl(p->fd, BIOCSETF, (caddr_t)fp) < 0) {
		snprintf(p->errbuf, PCAP_ERRBUF_SIZE, "BIOCSETF: %s",
		    pcap_strerror(errno));
		return (-1);
	}
	p->md.use_bpf = 1;	/* filtering in the kernel */
	return (0);
}

static int
pcap_set_datalink_bpf(pcap_t *p, int dlt)
{
#ifdef BIOCSDLT
	if (ioctl(p->fd, BIOCSDLT, &dlt) == -1) {
		(void) snprintf(p->errbuf, sizeof(p->errbuf),
		    "Cannot set DLT %d: %s", dlt, strerror(errno));
		return (-1);
	}
#endif
	return (0);
}