mac80211: Check existence of generated monX device

Fix then case when netsniff-ng fails if there is already an existing
monX device while generating one.

Signed-off-by: Vadim Kochan <vadim4j@gmail.com>
Signed-off-by: Tobias Klauser <tklauser@distanz.ch>

3 files changed, 17 insertions, 3 deletions

diff --git a/dev.c b/dev.c
index b3249e6..45659a8 100644
--- a/dev.c
+++ b/dev.c
@@ -13,7 +13,7 @@
 #include "link.h"
 #include "built_in.h"
 
-int device_ifindex(const char *ifname)
+int device_ifindex_get(const char *ifname)
 {
 	int ret, sock, index;
 	struct ifreq ifr;
@@ -27,8 +27,8 @@ int device_ifindex(const char *ifname)
 	strlcpy(ifr.ifr_name, ifname, IFNAMSIZ);
 
 	ret = ioctl(sock, SIOCGIFINDEX, &ifr);
-	if (unlikely(ret))
-		panic("Cannot get ifindex from device!\n");
+	if (ret)
+		return -1;
 
 	index = ifr.ifr_ifindex;
 	close(sock);
@@ -36,6 +36,15 @@ int device_ifindex(const char *ifname)
 	return index;
 }
 
+int device_ifindex(const char *ifname)
+{
+	int index = device_ifindex_get(ifname);
+	if (unlikely(index <= 0))
+		panic("Cannot get ifindex from device!\n");
+
+	return index;
+}
+
 int device_type(const char *ifname)
 {
 	int ret, sock, type;
diff --git a/dev.h b/dev.h
index 2d5f056..adb1c43 100644
--- a/dev.h
+++ b/dev.h
@@ -7,6 +7,7 @@
 extern size_t device_mtu(const char *ifname);
 extern int device_address(const char *ifname, int af, struct sockaddr_storage *ss);
 extern int device_ifindex(const char *ifname);
+extern int device_ifindex_get(const char *ifname);
 extern int device_type(const char *ifname);
 extern short device_get_flags(const char *ifname);
 extern void device_set_flags(const char *ifname, const short flags);
diff --git a/mac80211.c b/mac80211.c
index c089574..09f15b7 100644
--- a/mac80211.c
+++ b/mac80211.c
@@ -226,6 +226,10 @@ void enter_rfmon_mac80211(const char *device, char **mondev)
 		char mondevice[32];
 
 		slprintf(mondevice, sizeof(mondevice), "mon%u", n);
+
+		if (device_ifindex_get(mondevice) > 0)
+			continue;
+
 		ret = nl80211_add_mon_if(&nlstate, device, mondevice);
 		if (ret == 0) {
 			*mondev = xstrdup(mondevice);