c - 如何向libnl发送单 channel 扫描请求，并接收相应 channel 的单 channel 扫描完成响应

Question

我正在向 libnl 发送单个 SSID 和频率进行扫描，但我得到了多个扫描结果以及我请求的 SSID 和频率，但我需要单个扫描结果(仅适用于请求的 SSID)，如何实现这一点。请帮助我，我也发送了我的代码。该代码将运行。

编译:gcc -g -o scan scantesthandler.c -L/usr/lib/i386-linux-gnu/libnl.so -lnl

使用调试日志运行:NLCB=debug ./scan

#include<assert.h>
#include<errno.h>
#include<ifaddrs.h>
#include<netdb.h>
#include<stddef.h>
#include <string.h>
#include <time.h>
#include <unistd.h>
#include <sys/socket.h>
#include <asm/types.h>
#include <linux/rtnetlink.h>
#include <netlink/netlink.h>
#include <netlink/msg.h>
#include <netlink/cache.h>
#include <netlink/socket.h>
#include <netlink/genl/genl.h>
#include <netlink/genl/ctrl.h>
#include <stdlib.h>
#include <netlink/genl/genl.h>
#include <netlink/genl/ctrl.h>
#include <netlink/route/link.h>
#include <linux/nl80211.h>

static int expectedId;
static int ifIndex;
struct wpa_scan_res 
{
unsigned char bssid[6]; 
int freq;
};

static int error_handler(struct sockaddr_nl *nla, struct nlmsgerr *err, void *arg) 
{

int *ret = arg;
*ret = err->error;
return NL_SKIP;
}

static int finish_handler(struct nl_msg *msg, void *arg) 
{

int *ret = arg;
*ret = 0;
return NL_SKIP;
}
static int ack_handler(struct nl_msg *msg, void *arg)
{
int *err = arg;
*err = 0;
return NL_STOP;
}

static int bss_info_handler(struct nl_msg *msg, void *arg)
{

printf("\nFunction: %s, Line: %d\n",__FUNCTION__,__LINE__);
struct nlattr *tb[NL80211_ATTR_MAX + 1];
struct genlmsghdr *gnlh = nlmsg_data(nlmsg_hdr(msg));
struct nlattr *bss[NL80211_BSS_MAX + 1];
static struct nla_policy bss_policy[NL80211_BSS_MAX + 1] = {
[NL80211_BSS_BSSID] = { .type = NLA_UNSPEC },
[NL80211_BSS_FREQUENCY] = { .type = NLA_U32 },
[NL80211_BSS_TSF] = { .type = NLA_U64 },
[NL80211_BSS_BEACON_INTERVAL] = { .type = NLA_U16 },
[NL80211_BSS_CAPABILITY] = { .type = NLA_U16 },
[NL80211_BSS_INFORMATION_ELEMENTS] = { .type = NLA_UNSPEC },
[NL80211_BSS_SIGNAL_MBM] = { .type = NLA_U32 },
[NL80211_BSS_SIGNAL_UNSPEC] = { .type = NLA_U8 },
[NL80211_BSS_STATUS] = { .type = NLA_U32 },
[NL80211_BSS_SEEN_MS_AGO] = { .type = NLA_U32 },
[NL80211_BSS_BEACON_IES] = { .type = NLA_UNSPEC },
};
struct wpa_scan_res *r = NULL;

r = (struct wpa_scan_res*)malloc(sizeof(struct wpa_scan_res));

nla_parse(tb, NL80211_ATTR_MAX, genlmsg_attrdata(gnlh, 0),
genlmsg_attrlen(gnlh, 0), NULL);
if (!tb[NL80211_ATTR_BSS])
return NL_SKIP;
if (nla_parse_nested(bss, NL80211_BSS_MAX, tb[NL80211_ATTR_BSS],
bss_policy))
return NL_SKIP;
if (bss[NL80211_BSS_BSSID])

memcpy(r->bssid, nla_data(bss[NL80211_BSS_BSSID]),6);
if (bss[NL80211_BSS_FREQUENCY])
r->freq = nla_get_u32(bss[NL80211_BSS_FREQUENCY]);


printf("\nFrequency: %d ,BSSID: %2x:%2x:%2x:%2x:%2x:%2x",r->freq,r->bssid[0],r->bssid[1],r->bssid[2],r->bssid[3],r->bssid[4],r->bssid[5]);
return NL_SKIP;
}


static struct nl_msg* nl80211_scan_common(uint8_t cmd, int expectedId)
{
const char* ssid = "amitssid";

int ret;

struct nl_msg *msg;
int err;
size_t i;
int flags = 0,ifIndex;

msg = nlmsg_alloc();
if (!msg)
return NULL;

 // setup the message
if(NULL==genlmsg_put(msg, 0, 0, expectedId, 0, flags, cmd, 0))
{
printf("\nError return genlMsg_put\n");
}
else
{

printf("\nSuccess genlMsg_put\n");
}

ifIndex = if_nametoindex("wlan1");

if(nla_put_u32(msg, NL80211_ATTR_IFINDEX, ifIndex) < 0)
{

goto fail;
}

struct nl_msg *ssids = nlmsg_alloc();
if(nla_put(ssids, 1,strlen(ssid) ,ssid) <0)
{

nlmsg_free(ssids);
goto fail;
}

err =   nla_put_nested(msg,  NL80211_ATTR_SCAN_SSIDS,ssids);
nlmsg_free(ssids);
if (err < 0)
goto fail;

struct nl_msg *freqs = nlmsg_alloc();

if( nla_put_u32(freqs,1 ,2437) < 0) //amitssid
{
printf("\nnla_put_fail\n");
goto fail;
}
else
{
printf("\nnla_put_u32 pass\n");
}

//add message attributes
if(nla_put_nested(msg, NL80211_FREQUENCY_ATTR_FREQ,freqs) < 0)
{
printf("\nnla_put_nested failing:\n");
}
else
{
printf("\nnla_put_nested pass\n");
}

nlmsg_free(freqs);
if (err < 0)
goto fail;

return msg;

nla_put_failure:
printf("\nnla_put_failure\n");
nlmsg_free(msg);
return NULL;


fail:
nlmsg_free(msg);
return NULL;

}
int main(int argc, char** argv)
{

struct nl_msg *msg= NULL;
int ret = -1;
struct nl_cb *cb = NULL;
int err = -ENOMEM;
int returnvalue,getret;
int ifIndex, callbackret=-1;
struct nl_sock* sk = (void*)nl_handle_alloc();
if(sk == NULL)
{
printf("\nmemory error\n");
return;
}

cb = nl_cb_alloc(NL_CB_CUSTOM);
if(cb == NULL)
{
printf("\nfailed to allocate netlink callback\n");
}

enum nl80211_commands cmd;
if(genl_connect((void*)sk))
{
printf("\nConnected failed\n");
return;
}

//find the nl80211 driverID
expectedId = genl_ctrl_resolve((void*)sk, "nl80211");

if(expectedId < 0)
{
printf("\nnegative error code returned\n");
return;
}
else
{

printf("\ngenl_ctrl_resolve returned:%d\n",expectedId);
}


msg = nl80211_scan_common(NL80211_CMD_TRIGGER_SCAN, expectedId);
if (!msg)
{
printf("\nmsgbal:\n");
return -1;
}

err = nl_send_auto_complete((void*)sk, msg);
if (err < 0)
goto out;
else
{
printf("\nSent successfully\n");

}
err = 1;
nl_cb_err(cb,NL_CB_CUSTOM,error_handler,&err);
nl_cb_set(cb,NL_CB_FINISH,NL_CB_CUSTOM,finish_handler,&err);
nl_cb_set(cb,NL_CB_ACK,NL_CB_CUSTOM,ack_handler,&err);


callbackret = nl_cb_set(cb,NL_CB_VALID,NL_CB_CUSTOM,bss_info_handler,&err);

if(callbackret < 0)
{
printf("\n*************CallbackRet failed:***************** %d\n",callbackret);
}
else
{
printf("\n*************CallbackRet pass:***************** %d\n",callbackret);
}


returnvalue=nl_recvmsgs((void*)sk,cb);
printf("\n returnval:%d\n",returnvalue);

nlmsg_free(msg);
msg = NULL;
msg = nlmsg_alloc();
if (!msg)
return -1;

if(NULL==genlmsg_put(msg, 0, 0, expectedId, 0, NLM_F_DUMP, NL80211_CMD_GET_SCAN, 0))
{
printf("\nError return genlMsg_put\n");
}
else
{

printf("\nSuccess genlMsg_put\n");
}

ifIndex = if_nametoindex("wlan1");
printf("\nGet Scaninterface returned :%d\n",ifIndex);

nla_put_u32(msg,NL80211_ATTR_IFINDEX,ifIndex);  

err = nl_send_auto_complete((void*)sk,msg);
if(err < 0) goto out;

err = 1;
getret= nl_recvmsgs((void*)sk,cb);

printf("\nGt Scan resultreturn:%d\n",getret);

out:
nlmsg_free(msg);
return err;

nla_put_failure:
printf("\nnla_put_failure\n");
nlmsg_free(msg);
return err;
}

您只需将此代码复制并粘贴到您的系统上并运行即可。

Answer 1

据我所知(并且已经看到)，扫描命令和结果取决于供应商的设备驱动程序。可以肯定的是，没有选项可以扫描特定的 ssid；相反，您可以做的是获取所有扫描结果并循环检查 ssid 是否在列表中(wpa_supplicant 使用此机制将网络配置与扫描结果进行匹配)。

现在对于频率，如果设备驱动程序具有该功能，则应该可以仅扫描特定 channel 。但通常扫描命令会扫描所有 channel 并返回 SSID(想想您的网络管理器；它显示为扫描命令找到的所有可用 SSID。这本质上是由设备驱动程序通过 cfg80211 发布的)。