Correctly raise on bad filter (#4241)

Author: gpotter2

scapy/arch/bpf/supersocket.py

@@ -214,8 +214,8 @@ def __init__(self,
                 try:
                     attach_filter(self.bpf_fd, filter, self.iface)
                     filter_attached = True
-                except ImportError as ex:
-                    warning("Cannot set filter: %s" % ex)
+                except (ImportError, Scapy_Exception) as ex:
+                    raise Scapy_Exception("Cannot set filter: %s" % ex)
         if NETBSD and filter_attached is False:
             # On NetBSD, a filter must be attached to an interface, otherwise
             # no frame will be received by os.read(). When no filter has been

scapy/arch/libpcap.py

@@ -162,6 +162,7 @@ def close(self):
             pcap_datalink,
             pcap_findalldevs,
             pcap_freealldevs,
+            pcap_geterr,
             pcap_if_t,
             pcap_lib_version,
             pcap_next_ex,
@@ -386,16 +387,16 @@ def fileno(self):
                 return cast(int, pcap_get_selectable_fd(self.pcap))
 
         def setfilter(self, f):
-            # type: (str) -> bool
+            # type: (str) -> None
             filter_exp = create_string_buffer(f.encode("utf8"))
-            if pcap_compile(self.pcap, byref(self.bpf_program), filter_exp, 1, -1) == -1:  # noqa: E501
-                log_runtime.error("Could not compile filter expression %s", f)
-                return False
-            else:
-                if pcap_setfilter(self.pcap, byref(self.bpf_program)) == -1:
-                    log_runtime.error("Could not set filter %s", f)
-                    return False
-            return True
+            if pcap_compile(self.pcap, byref(self.bpf_program), filter_exp, 1, -1) >= 0:  # noqa: E501
+                if pcap_setfilter(self.pcap, byref(self.bpf_program)) >= 0:
+                    # Success
+                    return
+            errstr = decode_locale_str(
+                bytearray(pcap_geterr(self.pcap)).strip(b"\x00")
+            )
+            raise Scapy_Exception("Cannot set filter: %s" % errstr)
 
         def setnonblock(self, i):
             # type: (bool) -> None

scapy/arch/linux.py

@@ -507,7 +507,7 @@ def __init__(self,
                 try:
                     attach_filter(self.ins, filter, self.iface)
                 except (ImportError, Scapy_Exception) as ex:
-                    log_runtime.error("Cannot set filter: %s", ex)
+                    raise Scapy_Exception("Cannot set filter: %s" % ex)
         if self.promisc:
             set_promisc(self.ins, self.iface)
         self.ins.bind((self.iface, type))

test/regression.uts

@@ -2262,6 +2262,15 @@ except Scapy_Exception:
 else:
     assert False
 
+= Check online sniff() with a bad filter
+~ needs_root tcpdump libpcap
+try:
+    sniff(timeout=0, filter="bad filter")
+except Scapy_Exception:
+    pass
+else:
+    assert False
+
 = Check offline sniff with lfilter
 assert len(sniff(offline=[IP()/UDP(), IP()/TCP()], lfilter=lambda x: TCP in x)) == 1