Merge pull request #2225 from gpotter2/tcpdump-fix

Fix tcpdump detection

Author: p-l-

scapy/arch/common.py

@@ -19,7 +19,6 @@
 from scapy.config import conf
 from scapy.data import MTU
 from scapy.error import Scapy_Exception
-from scapy.consts import OPENBSD
 import scapy.modules.six as six
 
 if not WINDOWS:
@@ -32,18 +31,18 @@ def _check_tcpdump():
     """
     Return True if the tcpdump command can be started
     """
-    with open(os.devnull, 'wb') as devnull:
-        try:
-            proc = subprocess.Popen([conf.prog.tcpdump, "--version"],
-                                    stdout=devnull, stderr=subprocess.STDOUT)
-        except OSError:
-            return False
-
-    if OPENBSD:
-        # 'tcpdump --version' returns 1 on OpenBSD 6.4
-        return proc.wait() == 1
-    else:
-        return proc.wait() == 0
+    try:
+        proc = subprocess.Popen(
+            [conf.prog.tcpdump, "--version"],
+            stdout=subprocess.PIPE,
+            stderr=subprocess.STDOUT
+        )
+        output = proc.communicate()[0]
+    except OSError:
+        return False
+
+    # On some systems, --version does not exist on tcpdump
+    return proc.returncode == 0 or output.startswith(b'Usage: tcpdump ')
 
 
 # This won't be used on Windows