pcap-bpf.c

Windows XP下的抓包程序实现

		u_int i;
		int is_ethernet;

		bdl.bfl_list = (u_int *) malloc(sizeof(u_int) * (bdl.bfl_len + 1));
		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));
			free(bdl.bfl_list);
			goto bad;
		}

		/*
		 * OK, for real Ethernet devices, add DLT_DOCSIS to the
		 * list, so that an application can let you choose it,
		 * in case you're capturing DOCSIS traffic that a Cisco
		 * Cable Modem Termination System is putting out onto
		 * an Ethernet (it doesn't put an Ethernet header onto
		 * the wire, it puts raw DOCSIS frames out on the wire
		 * inside the low-level Ethernet framing).
		 *
		 * A "real Ethernet device" is defined here as a device
		 * that has a link-layer type of DLT_EN10MB and that has
		 * no alternate link-layer types; that's done to exclude
		 * 802.11 interfaces (which might or might not be the
		 * right thing to do, but I suspect it is - Ethernet <->
		 * 802.11 bridges would probably badly mishandle frames
		 * that don't have Ethernet headers).
		 */
		if (p->linktype == DLT_EN10MB) {
			is_ethernet = 1;
			for (i = 0; i < bdl.bfl_len; i++) {
				if (bdl.bfl_list[i] != DLT_EN10MB) {
					is_ethernet = 0;
					break;
				}
			}
			if (is_ethernet) {
				/*
				 * We reserved one more slot at the end of
				 * the list.
				 */
				bdl.bfl_list[bdl.bfl_len] = DLT_DOCSIS;
				bdl.bfl_len++;
			}
		}
		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

	/*
	 * If this is an Ethernet device, and we don't have a DLT_ list,
	 * give it a list with DLT_EN10MB and DLT_DOCSIS.  (That'd give
	 * 802.11 interfaces DLT_DOCSIS, which isn't the right thing to
	 * do, but there's not much we can do about that without finding
	 * some other way of determining whether it's an Ethernet or 802.11
	 * device.)
	 */
	if (p->linktype == DLT_EN10MB && p->dlt_count == 0) {
		p->dlt_list = (u_int *) malloc(sizeof(u_int) * 2);
		/*
		 * If that fails, just leave the list empty.
		 */
		if (p->dlt_list != NULL) {
			p->dlt_list[0] = DLT_EN10MB;
			p->dlt_list[1] = DLT_DOCSIS;
			p->dlt_count = 2;
		}
	}
		
#if defined(BIOCGHDRCMPLT) && defined(BIOCSHDRCMPLT)
	/*
	 * Do a BIOCSHDRCMPLT, if defined, to turn that flag on, so
	 * the link-layer source address isn't forcibly overwritten.
	 * (Should we ignore errors?  Should we do this only if
	 * we're open for writing?)
	 *
	 * XXX - I seem to remember some packet-sending bug in some
	 * BSDs - check CVS log for "bpf.c"?
	 */
	if (ioctl(fd, BIOCSHDRCMPLT, &spoof_eth_src) == -1) {
		(void)snprintf(ebuf, PCAP_ERRBUF_SIZE,
		    "BIOCSHDRCMPLT: %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

	/*
	 * If there's no filter program installed, there's
	 * no indication to the kernel of what the snapshot
	 * length should be, so no snapshotting is done.
	 *
	 * Therefore, when we open the device, we install
	 * an "accept everything" filter with the specified
	 * snapshot length.
	 */
	total_insn.code = (u_short)(BPF_RET | BPF_K);
	total_insn.jt = 0;
	total_insn.jf = 0;
	total_insn.k = snaplen;

	total_prog.bf_len = 1;
	total_prog.bf_insns = &total_insn;
	if (ioctl(p->fd, BIOCSETF, (caddr_t)&total_prog) < 0) {
		snprintf(ebuf, PCAP_ERRBUF_SIZE, "BIOCSETF: %s",
		    pcap_strerror(errno));
		goto bad;
	}

	/*
	 * 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?
	 */
	p->selectable_fd = p->fd;	/* assume select() works until we know otherwise */
	if (uname(&osinfo) == 0) {
		/*
		 * We can check what OS this is.
		 */
		if (strcmp(osinfo.sysname, "FreeBSD") == 0) {
			if (strncmp(osinfo.release, "4.3-", 4) == 0 ||
			     strncmp(osinfo.release, "4.4-", 4) == 0)
				p->selectable_fd = -1;
		}
	}

	p->read_op = pcap_read_bpf;
	p->inject_op = pcap_inject_bpf;
	p->setfilter_op = pcap_setfilter_bpf;
	p->setdirection_op = pcap_setdirection_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_common;

	return (p);
 bad:
	(void)close(fd);
	if (p->dlt_list != NULL)
		free(p->dlt_list);
	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 */

	/*
	 * Discard any previously-received packets, as they might have
	 * passed whatever filter was formerly in effect, but might
	 * not pass this filter (BIOCSETF discards packets buffered
	 * in the kernel, so you can lose packets in any case).
	 */
	p->cc = 0;
	return (0);
}

/*
 * Set direction flag: Which packets do we accept on a forwarding
 * single device? IN, OUT or both?
 */
static int
pcap_setdirection_bpf(pcap_t *p, pcap_direction_t d)
{
#ifdef BIOCSSEESENT
	u_int seesent;
#endif

	/*
	 * We don't support PCAP_D_OUT.
	 */
	if (d == PCAP_D_OUT) {
		snprintf(p->errbuf, sizeof(p->errbuf),
		    "Setting direction to PCAP_D_OUT is not supported on BPF");
		return -1;
	}
#ifdef BIOCSSEESENT
	seesent = (d == PCAP_D_INOUT);
	if (ioctl(p->fd, BIOCSSEESENT, &seesent) == -1) {
		(void) snprintf(p->errbuf, sizeof(p->errbuf),
		    "Cannot set direction to %s: %s",
		        (d == PCAP_D_INOUT) ? "PCAP_D_INOUT" : "PCAP_D_IN",
			strerror(errno));
		return (-1);
	}
	return (0);
#else
	(void) snprintf(p->errbuf, sizeof(p->errbuf),
	    "This system doesn't support BIOCSSEESENT, so the direction can't be set");
	return (-1);
#endif
}

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);
}