Make the checks and adjustment of the snapshot length module-dependent.

Also, initialize the snapshot length to 0, meaning "not specified", so
that the default snapshot length, if not specified, is also
module-dependent.

That way, D-Bus has a maximum and default of 128MB, as that's the
maximum message size, but other capture devices have the current
MAXIMUM_SNAPLEN, so we can handle full-size D-Bus messages without
advertising an overly-large snapshot length for other devices,
potentially causing libpcap and programs using it or reading libpcap
files to allocate overly-large buffers for other capture devices.

1 files changed, 11 insertions, 0 deletions

diff --git a/pcap-dos.c b/pcap-dos.c
index 60e9d890..7bffce5a 100644
--- a/pcap-dos.c
+++ b/pcap-dos.c
@@ -174,6 +174,17 @@ static int pcap_activate_dos (pcap_t *pcap)
     return (PCAP_ERROR_RFMON_NOTSUP);
   }
 
+  /*
+   * Turn a negative snapshot value (invalid), a snapshot value of
+   * 0 (unspecified), or a value bigger than the normal maximum
+   * value, into the maximum allowed value.
+   *
+   * If some application really *needs* a bigger snapshot
+   * length, we should just increase MAXIMUM_SNAPLEN.
+   */
+  if (pcap->snapshot <= 0 || pcap->snapshot > MAXIMUM_SNAPLEN)
+    pcap->snapshot = MAXIMUM_SNAPLEN;
+
   if (pcap->snapshot < ETH_MIN+8)
       pcap->snapshot = ETH_MIN+8;