From f66819c145dbc90bb8000e81ad3a89877e1f3a42 Mon Sep 17 00:00:00 2001
From: oblique <psyberbits@gmail.com>
Date: Sat, 6 Sep 2014 21:49:52 +0300
Subject: [PATCH] Check if the user passed a valid interface

---
 create_ap | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/create_ap b/create_ap
index da6c5aa..bf5460a 100755
--- a/create_ap
+++ b/create_ap
@@ -82,6 +82,11 @@ version_cmp() {
 
 USE_IWCONFIG=0
 
+is_interface() {
+    [[ -z "$1" ]] && return 1
+    ip link show $1 > /dev/null 2>&1
+}
+
 is_wifi_interface() {
     which iw > /dev/null 2>&1 && iw dev $1 info > /dev/null 2>&1 && return 0
     if which iwconfig > /dev/null 2>&1 && iwconfig $1 > /dev/null 2>&1; then
@@ -579,6 +584,11 @@ else
     fi
 fi
 
+if [[ "$SHARE_METHOD" != "none" ]] && ! is_interface $INTERNET_IFACE; then
+    echo "ERROR: '${INTERNET_IFACE}' is not an interface" >&2
+    exit 1
+fi
+
 if [[ "$SHARE_METHOD" == "bridge" ]]; then
     OLD_BRIDGE_IPTABLES=$(cat /proc/sys/net/bridge/bridge-nf-call-iptables)