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* WPA Supplicant - Layer2 packet handling with WinPcap RX thread
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* Copyright (c) 2003-2006, Jouni Malinen <j@w1.fi>
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License version 2 as
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* published by the Free Software Foundation.
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* Alternatively, this software may be distributed under the terms of BSD
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* See README and COPYING for more details.
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* This l2_packet implementation is explicitly for WinPcap and Windows events.
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* l2_packet_pcap.c has support for WinPcap, but it requires polling to receive
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* frames which means relatively long latency for EAPOL RX processing. The
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* implementation here uses a separate thread to allow WinPcap to be receiving
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* all the time to reduce latency for EAPOL receiving from about 100 ms to 3 ms
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* when comparing l2_packet_pcap.c to l2_packet_winpcap.c. Extra sleep of 50 ms
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* is added in to receive thread whenever no EAPOL frames has been received for
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* a while. Whenever an EAPOL handshake is expected, this sleep is removed.
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* The RX thread receives a frame and signals main thread through Windows event
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* about the availability of a new frame. Processing the received frame is
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* synchronized with pair of Windows events so that no extra buffer or queuing
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* mechanism is needed. This implementation requires Windows specific event
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* loop implementation, i.e., eloop_win.c.
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* WinPcap has pcap_getevent() that could, in theory at least, be used to
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* implement this kind of waiting with a simpler single-thread design. However,
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* that event handle is not really signaled immediately when receiving each
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* frame, so it does not really work for this kind of use.
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#include "l2_packet.h"
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static const u8 pae_group_addr[ETH_ALEN] =
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{ 0x01, 0x80, 0xc2, 0x00, 0x00, 0x03 };
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* Number of pcap_dispatch() iterations to do without extra wait after each
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* received EAPOL packet or authentication notification. This is used to reduce
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* latency for EAPOL receive.
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static const size_t no_wait_count = 750;
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struct l2_packet_data {
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unsigned int num_fast_poll;
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u8 own_addr[ETH_ALEN];
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void (*rx_callback)(void *ctx, const u8 *src_addr,
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const u8 *buf, size_t len);
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void *rx_callback_ctx;
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int l2_hdr; /* whether to include layer 2 (Ethernet) header in calls to
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* rx_callback and l2_packet_send() */
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HANDLE rx_avail, rx_done, rx_thread, rx_thread_done, rx_notify;
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int l2_packet_get_own_addr(struct l2_packet_data *l2, u8 *addr)
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os_memcpy(addr, l2->own_addr, ETH_ALEN);
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int l2_packet_send(struct l2_packet_data *l2, const u8 *dst_addr, u16 proto,
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const u8 *buf, size_t len)
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struct l2_ethhdr *eth;
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ret = pcap_sendpacket(l2->pcap, buf, len);
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size_t mlen = sizeof(*eth) + len;
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eth = os_malloc(mlen);
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os_memcpy(eth->h_dest, dst_addr, ETH_ALEN);
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os_memcpy(eth->h_source, l2->own_addr, ETH_ALEN);
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eth->h_proto = htons(proto);
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os_memcpy(eth + 1, buf, len);
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ret = pcap_sendpacket(l2->pcap, (u8 *) eth, mlen);
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/* pcap_dispatch() callback for the RX thread */
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static void l2_packet_receive_cb(u_char *user, const struct pcap_pkthdr *hdr,
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const u_char *pkt_data)
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struct l2_packet_data *l2 = (struct l2_packet_data *) user;
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struct l2_ethhdr *ethhdr;
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if (pkt_data == NULL || hdr->caplen < sizeof(*ethhdr))
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ethhdr = (struct l2_ethhdr *) pkt_data;
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l2->rx_buf = (u8 *) ethhdr;
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l2->rx_len = hdr->caplen;
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l2->rx_buf = (u8 *) (ethhdr + 1);
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l2->rx_len = hdr->caplen - sizeof(*ethhdr);
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l2->rx_src = ethhdr->h_source;
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SetEvent(l2->rx_avail);
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WaitForSingleObject(l2->rx_done, INFINITE);
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ResetEvent(l2->rx_done);
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l2->rx_no_wait = no_wait_count;
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/* main RX loop that is running in a separate thread */
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static DWORD WINAPI l2_packet_receive_thread(LPVOID arg)
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struct l2_packet_data *l2 = arg;
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while (l2->running) {
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pcap_dispatch(l2->pcap, 1, l2_packet_receive_cb,
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if (l2->rx_no_wait > 0)
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if (WaitForSingleObject(l2->rx_notify,
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l2->rx_no_wait ? 0 : 50) ==
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l2->rx_no_wait = no_wait_count;
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ResetEvent(l2->rx_notify);
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SetEvent(l2->rx_thread_done);
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/* main thread RX event handler */
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static void l2_packet_rx_event(void *eloop_data, void *user_data)
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struct l2_packet_data *l2 = eloop_data;
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l2->rx_callback(l2->rx_callback_ctx, l2->rx_src, l2->rx_buf,
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ResetEvent(l2->rx_avail);
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SetEvent(l2->rx_done);
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static int l2_packet_init_libpcap(struct l2_packet_data *l2,
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unsigned short protocol)
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bpf_u_int32 pcap_maskp, pcap_netp;
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char pcap_filter[200], pcap_err[PCAP_ERRBUF_SIZE];
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struct bpf_program pcap_fp;
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pcap_lookupnet(l2->ifname, &pcap_netp, &pcap_maskp, pcap_err);
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l2->pcap = pcap_open_live(l2->ifname, 2500, 0, 1, pcap_err);
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if (l2->pcap == NULL) {
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fprintf(stderr, "pcap_open_live: %s\n", pcap_err);
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fprintf(stderr, "ifname='%s'\n", l2->ifname);
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os_snprintf(pcap_filter, sizeof(pcap_filter),
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"not ether src " MACSTR " and "
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"( ether dst " MACSTR " or ether dst " MACSTR " ) and "
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MAC2STR(l2->own_addr), /* do not receive own packets */
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MAC2STR(l2->own_addr), MAC2STR(pae_group_addr),
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if (pcap_compile(l2->pcap, &pcap_fp, pcap_filter, 1, pcap_netp) < 0) {
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fprintf(stderr, "pcap_compile: %s\n", pcap_geterr(l2->pcap));
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if (pcap_setfilter(l2->pcap, &pcap_fp) < 0) {
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fprintf(stderr, "pcap_setfilter: %s\n", pcap_geterr(l2->pcap));
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pcap_freecode(&pcap_fp);
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struct l2_packet_data * l2_packet_init(
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const char *ifname, const u8 *own_addr, unsigned short protocol,
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void (*rx_callback)(void *ctx, const u8 *src_addr,
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const u8 *buf, size_t len),
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void *rx_callback_ctx, int l2_hdr)
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struct l2_packet_data *l2;
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l2 = os_zalloc(sizeof(struct l2_packet_data));
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if (os_strncmp(ifname, "\\Device\\NPF_", 12) == 0)
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os_strlcpy(l2->ifname, ifname, sizeof(l2->ifname));
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os_snprintf(l2->ifname, sizeof(l2->ifname), "\\Device\\NPF_%s",
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l2->rx_callback = rx_callback;
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l2->rx_callback_ctx = rx_callback_ctx;
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os_memcpy(l2->own_addr, own_addr, ETH_ALEN);
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if (l2_packet_init_libpcap(l2, protocol)) {
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l2->rx_avail = CreateEvent(NULL, TRUE, FALSE, NULL);
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l2->rx_done = CreateEvent(NULL, TRUE, FALSE, NULL);
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l2->rx_notify = CreateEvent(NULL, TRUE, FALSE, NULL);
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if (l2->rx_avail == NULL || l2->rx_done == NULL ||
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l2->rx_notify == NULL) {
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CloseHandle(l2->rx_avail);
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CloseHandle(l2->rx_done);
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CloseHandle(l2->rx_notify);
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pcap_close(l2->pcap);
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eloop_register_event(l2->rx_avail, sizeof(l2->rx_avail),
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l2_packet_rx_event, l2, NULL);
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l2->rx_thread = CreateThread(NULL, 0, l2_packet_receive_thread, l2, 0,
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static void l2_packet_deinit_timeout(void *eloop_ctx, void *timeout_ctx)
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struct l2_packet_data *l2 = eloop_ctx;
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if (l2->rx_thread_done &&
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WaitForSingleObject(l2->rx_thread_done, 2000) != WAIT_OBJECT_0) {
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wpa_printf(MSG_DEBUG, "l2_packet_winpcap: RX thread did not "
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TerminateThread(l2->rx_thread, 0);
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CloseHandle(l2->rx_thread_done);
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CloseHandle(l2->rx_thread);
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pcap_close(l2->pcap);
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eloop_unregister_event(l2->rx_avail, sizeof(l2->rx_avail));
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CloseHandle(l2->rx_avail);
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CloseHandle(l2->rx_done);
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CloseHandle(l2->rx_notify);
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void l2_packet_deinit(struct l2_packet_data *l2)
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l2->rx_thread_done = CreateEvent(NULL, TRUE, FALSE, NULL);
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pcap_breakloop(l2->pcap);
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* RX thread may be waiting in l2_packet_receive_cb() for l2->rx_done
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* event and this event is set in l2_packet_rx_event(). However,
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* l2_packet_deinit() may end up being called from l2->rx_callback(),
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* so we need to return from here and complete deinitialization in
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* a registered timeout to avoid having to forcefully kill the RX
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eloop_register_timeout(0, 0, l2_packet_deinit_timeout, l2, NULL);
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int l2_packet_get_ip_addr(struct l2_packet_data *l2, char *buf, size_t len)
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pcap_if_t *devs, *dev;
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struct pcap_addr *addr;
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struct sockaddr_in *saddr;
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char err[PCAP_ERRBUF_SIZE + 1];
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if (pcap_findalldevs(&devs, err) < 0) {
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wpa_printf(MSG_DEBUG, "pcap_findalldevs: %s\n", err);
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for (dev = devs; dev && !found; dev = dev->next) {
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if (os_strcmp(dev->name, l2->ifname) != 0)
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addr = dev->addresses;
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saddr = (struct sockaddr_in *) addr->addr;
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if (saddr && saddr->sin_family == AF_INET) {
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os_strlcpy(buf, inet_ntoa(saddr->sin_addr),
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pcap_freealldevs(devs);
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return found ? 0 : -1;
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void l2_packet_notify_auth_start(struct l2_packet_data *l2)
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SetEvent(l2->rx_notify);
added
removed
src/l2_packet/l2_packet_winpcap.c
