OpenWrt – Rev 1
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/*
* iwcap.c - A simply radiotap capture utility outputting pcap dumps
*
* Copyright 2012 Jo-Philipp Wich <jo@mein.io>
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*
*/
#include <stdio.h>
#include <stdint.h>
#include <stdlib.h>
#include <stdarg.h>
#include <unistd.h>
#include <string.h>
#include <signal.h>
#include <syslog.h>
#include <errno.h>
#include <byteswap.h>
#include <sys/stat.h>
#include <sys/time.h>
#include <sys/ioctl.h>
#include <sys/socket.h>
#include <net/ethernet.h>
#include <net/if.h>
#include <netinet/in.h>
#include <linux/if_packet.h>
#define ARPHRD_IEEE80211_RADIOTAP 803
#define DLT_IEEE802_11_RADIO 127
#define LEN_IEEE802_11_HDR 32
#define FRAMETYPE_MASK 0xFC
#define FRAMETYPE_BEACON 0x80
#define FRAMETYPE_DATA 0x08
#if __BYTE_ORDER == __BIG_ENDIAN
#define le16(x) __bswap_16(x)
#else
#define le16(x) (x)
#endif
uint8_t run_dump = 0;
uint8_t run_stop = 0;
uint8_t run_daemon = 0;
uint32_t frames_captured = 0;
uint32_t frames_filtered = 0;
int capture_sock = -1;
const char *ifname = NULL;
struct ringbuf {
uint32_t len; /* number of slots */
uint32_t fill; /* last used slot */
uint32_t slen; /* slot size */
void *buf; /* ring memory */
};
struct ringbuf_entry {
uint32_t len; /* used slot memory */
uint32_t olen; /* original data size */
uint32_t sec; /* epoch of slot creation */
uint32_t usec; /* epoch microseconds */
};
typedef struct pcap_hdr_s {
uint32_t magic_number; /* magic number */
uint16_t version_major; /* major version number */
uint16_t version_minor; /* minor version number */
int32_t thiszone; /* GMT to local correction */
uint32_t sigfigs; /* accuracy of timestamps */
uint32_t snaplen; /* max length of captured packets, in octets */
uint32_t network; /* data link type */
} pcap_hdr_t;
typedef struct pcaprec_hdr_s {
uint32_t ts_sec; /* timestamp seconds */
uint32_t ts_usec; /* timestamp microseconds */
uint32_t incl_len; /* number of octets of packet saved in file */
uint32_t orig_len; /* actual length of packet */
} pcaprec_hdr_t;
typedef struct ieee80211_radiotap_header {
u_int8_t it_version; /* set to 0 */
u_int8_t it_pad;
u_int16_t it_len; /* entire length */
u_int32_t it_present; /* fields present */
} __attribute__((__packed__)) radiotap_hdr_t;
int check_type(void)
{
struct ifreq ifr;
strncpy(ifr.ifr_name, ifname, IFNAMSIZ);
if (ioctl(capture_sock, SIOCGIFHWADDR, &ifr) < 0)
return -1;
return (ifr.ifr_hwaddr.sa_family == ARPHRD_IEEE80211_RADIOTAP);
}
int set_promisc(int on)
{
struct ifreq ifr;
strncpy(ifr.ifr_name, ifname, IFNAMSIZ);
if (ioctl(capture_sock, SIOCGIFFLAGS, &ifr) < 0)
return -1;
if (on && !(ifr.ifr_flags & IFF_PROMISC))
{
ifr.ifr_flags |= IFF_PROMISC;
if (ioctl(capture_sock, SIOCSIFFLAGS, &ifr))
return -1;
return 1;
}
else if (!on && (ifr.ifr_flags & IFF_PROMISC))
{
ifr.ifr_flags &= ~IFF_PROMISC;
if (ioctl(capture_sock, SIOCSIFFLAGS, &ifr))
return -1;
return 1;
}
return 0;
}
void sig_dump(int sig)
{
run_dump = 1;
}
void sig_teardown(int sig)
{
run_stop = 1;
}
void write_pcap_header(FILE *o)
{
pcap_hdr_t ghdr = {
.magic_number = 0xa1b2c3d4,
.version_major = 2,
.version_minor = 4,
.thiszone = 0,
.sigfigs = 0,
.snaplen = 0xFFFF,
.network = DLT_IEEE802_11_RADIO
};
fwrite(&ghdr, 1, sizeof(ghdr), o);
}
void write_pcap_frame(FILE *o, uint32_t *sec, uint32_t *usec,
uint16_t len, uint16_t olen)
{
struct timeval tv;
pcaprec_hdr_t fhdr;
if (!sec || !usec)
{
gettimeofday(&tv, NULL);
}
else
{
tv.tv_sec = *sec;
tv.tv_usec = *usec;
}
fhdr.ts_sec = tv.tv_sec;
fhdr.ts_usec = tv.tv_usec;
fhdr.incl_len = len;
fhdr.orig_len = olen;
fwrite(&fhdr, 1, sizeof(fhdr), o);
}
struct ringbuf * ringbuf_init(uint32_t num_item, uint16_t len_item)
{
static struct ringbuf r;
if (len_item <= 0)
return NULL;
r.buf = malloc(num_item * (len_item + sizeof(struct ringbuf_entry)));
if (r.buf)
{
r.len = num_item;
r.fill = 0;
r.slen = (len_item + sizeof(struct ringbuf_entry));
memset(r.buf, 0, num_item * len_item);
return &r;
}
return NULL;
}
struct ringbuf_entry * ringbuf_add(struct ringbuf *r)
{
struct timeval t;
struct ringbuf_entry *e;
gettimeofday(&t, NULL);
e = r->buf + (r->fill++ * r->slen);
r->fill %= r->len;
memset(e, 0, r->slen);
e->sec = t.tv_sec;
e->usec = t.tv_usec;
return e;
}
struct ringbuf_entry * ringbuf_get(struct ringbuf *r, int i)
{
struct ringbuf_entry *e = r->buf + (((r->fill + i) % r->len) * r->slen);
if (e->len > 0)
return e;
return NULL;
}
void ringbuf_free(struct ringbuf *r)
{
free(r->buf);
memset(r, 0, sizeof(*r));
}
void msg(const char *fmt, ...)
{
va_list ap;
va_start(ap, fmt);
if (run_daemon)
vsyslog(LOG_INFO | LOG_USER, fmt, ap);
else
vfprintf(stderr, fmt, ap);
va_end(ap);
}
int main(int argc, char **argv)
{
int i, n;
struct ringbuf *ring;
struct ringbuf_entry *e;
struct sockaddr_ll local = {
.sll_family = AF_PACKET,
.sll_protocol = htons(ETH_P_ALL)
};
radiotap_hdr_t *rhdr;
uint8_t frametype;
uint8_t pktbuf[0xFFFF];
ssize_t pktlen;
FILE *o;
int opt;
uint8_t promisc = 0;
uint8_t streaming = 0;
uint8_t foreground = 0;
uint8_t filter_data = 0;
uint8_t filter_beacon = 0;
uint8_t header_written = 0;
uint32_t ringsz = 1024 * 1024; /* 1 Mbyte ring buffer */
uint16_t pktcap = 256; /* truncate frames after 265KB */
const char *output = NULL;
while ((opt = getopt(argc, argv, "i:r:c:o:sfhBD")) != -1)
{
switch (opt)
{
case 'i':
ifname = optarg;
if (!(local.sll_ifindex = if_nametoindex(ifname)))
{
msg("Unknown interface '%s'\n", ifname);
return 2;
}
break;
case 'r':
ringsz = atoi(optarg);
if (ringsz < (3 * pktcap))
{
msg("Ring size of %d bytes is too short, "
"must be at least %d bytes\n", ringsz, 3 * pktcap);
return 3;
}
break;
case 'c':
pktcap = atoi(optarg);
if (pktcap <= (sizeof(radiotap_hdr_t) + LEN_IEEE802_11_HDR))
{
msg("Packet truncate after %d bytes is too short, "
"must be at least %d bytes\n",
pktcap, sizeof(radiotap_hdr_t) + LEN_IEEE802_11_HDR);
return 4;
}
break;
case 's':
streaming = 1;
break;
case 'o':
output = optarg;
break;
case 'B':
filter_beacon = 1;
break;
case 'D':
filter_data = 1;
break;
case 'f':
foreground = 1;
break;
case 'h':
msg(
"Usage:\n"
" %s -i {iface} -s [-b] [-d]\n"
" %s -i {iface} -o {file} [-r len] [-c len] [-B] [-D] [-f]\n"
"\n"
" -i iface\n"
" Specify interface to use, must be in monitor mode and\n"
" produce IEEE 802.11 Radiotap headers.\n\n"
" -s\n"
" Stream to stdout instead of Dumping to file on USR1.\n\n"
" -o file\n"
" Write current ringbuffer contents to given output file\n"
" on receipt of SIGUSR1.\n\n"
" -r len\n"
" Specify the amount of bytes to use for the ringbuffer.\n"
" The default length is %d bytes.\n\n"
" -c len\n"
" Truncate captured packets after given amount of bytes.\n"
" The default size limit is %d bytes.\n\n"
" -B\n"
" Don't store beacon frames in ring, default is keep.\n\n"
" -D\n"
" Don't store data frames in ring, default is keep.\n\n"
" -f\n"
" Do not daemonize but keep running in foreground.\n\n"
" -h\n"
" Display this help.\n\n",
argv[0], argv[0], ringsz, pktcap);
return 1;
}
}
if (!streaming && !output)
{
msg("No output file specified\n");
return 1;
}
if (streaming && output)
{
msg("The -s and -o options are exclusive\n");
return 1;
}
if (streaming && isatty(1))
{
msg("Refusing to stream into a terminal\n");
return 1;
}
if (!local.sll_ifindex)
{
msg("No interface specified\n");
return 2;
}
if (!check_type())
{
msg("Bad interface: not ARPHRD_IEEE80211_RADIOTAP\n");
return 2;
}
if ((capture_sock = socket(PF_PACKET, SOCK_RAW, htons(ETH_P_ALL))) < 0)
{
msg("Unable to create raw socket: %s\n",
strerror(errno));
return 6;
}
if (bind(capture_sock, (struct sockaddr *)&local, sizeof(local)) == -1)
{
msg("Unable to bind to interface: %s\n",
strerror(errno));
return 7;
}
if (!streaming)
{
if (!foreground)
{
switch (fork())
{
case -1:
msg("Unable to fork: %s\n", strerror(errno));
return 8;
case 0:
umask(0077);
chdir("/");
freopen("/dev/null", "r", stdin);
freopen("/dev/null", "w", stdout);
freopen("/dev/null", "w", stderr);
run_daemon = 1;
break;
default:
msg("Daemon launched ...\n");
return 0;
}
}
msg("Monitoring interface %s ...\n", ifname);
if (!(ring = ringbuf_init(ringsz / pktcap, pktcap)))
{
msg("Unable to allocate ring buffer: %s\n",
strerror(errno));
return 5;
}
msg(" * Using %d bytes ringbuffer with %d slots\n", ringsz, ring->len);
msg(" * Truncating frames at %d bytes\n", pktcap);
msg(" * Dumping data to file %s\n", output);
signal(SIGUSR1, sig_dump);
}
else
{
msg("Monitoring interface %s ...\n", ifname);
msg(" * Streaming data to stdout\n");
}
msg(" * Beacon frames are %sfiltered\n", filter_beacon ? "" : "not ");
msg(" * Data frames are %sfiltered\n", filter_data ? "" : "not ");
signal(SIGINT, sig_teardown);
signal(SIGTERM, sig_teardown);
promisc = set_promisc(1);
/* capture loop */
while (1)
{
if (run_dump)
{
msg("Dumping ring to %s ...\n", output);
if (!(o = fopen(output, "w")))
{
msg("Unable to open %s: %s\n",
output, strerror(errno));
}
else
{
write_pcap_header(o);
/* sig_dump packet buffer */
for (i = 0, n = 0; i < ring->len; i++)
{
if (!(e = ringbuf_get(ring, i)))
continue;
write_pcap_frame(o, &(e->sec), &(e->usec), e->len, e->olen);
fwrite((void *)e + sizeof(*e), 1, e->len, o);
n++;
}
fclose(o);
msg(" * %d frames captured\n", frames_captured);
msg(" * %d frames filtered\n", frames_filtered);
msg(" * %d frames dumped\n", n);
}
run_dump = 0;
}
if (run_stop)
{
msg("Shutting down ...\n");
if (promisc)
set_promisc(0);
if (ring)
ringbuf_free(ring);
return 0;
}
pktlen = recvfrom(capture_sock, pktbuf, sizeof(pktbuf), 0, NULL, 0);
frames_captured++;
/* check received frametype, if we should filter it, rewind the ring */
rhdr = (radiotap_hdr_t *)pktbuf;
if (pktlen <= sizeof(radiotap_hdr_t) || le16(rhdr->it_len) >= pktlen)
{
frames_filtered++;
continue;
}
frametype = *(uint8_t *)(pktbuf + le16(rhdr->it_len));
if ((filter_data && (frametype & FRAMETYPE_MASK) == FRAMETYPE_DATA) ||
(filter_beacon && (frametype & FRAMETYPE_MASK) == FRAMETYPE_BEACON))
{
frames_filtered++;
continue;
}
if (streaming)
{
if (!header_written)
{
write_pcap_header(stdout);
header_written = 1;
}
write_pcap_frame(stdout, NULL, NULL, pktlen, pktlen);
fwrite(pktbuf, 1, pktlen, stdout);
fflush(stdout);
}
else
{
e = ringbuf_add(ring);
e->olen = pktlen;
e->len = (pktlen > pktcap) ? pktcap : pktlen;
memcpy((void *)e + sizeof(*e), pktbuf, e->len);
}
}
return 0;
}