parser: Add dbus eavesdrop permission support to apparmor_parser

Allows for the policy writer to grant permission to eavesdrop on the
specified bus. Some example rules for granting the eavesdrop permission
are:

  # Grant send, receive, bind, and eavesdrop
  dbus,

  # Grant send, receive, bind, and eavesdrop on the session bus
  dbus bus=session,

  # Grant send and eavesdrop on the system bus
  dbus (send eavesdrop) bus=system,

  # Grant eavesdrop on any bus
  dbus eavesdrop,

Eavesdropping rules can contain the bus conditional. Any other
conditionals are not compatible with eavesdropping rules and the parser
will return an error.

Signed-off-by: Tyler Hicks <tyhicks@canonical.com>
Acked-by: Seth Arnold <seth.arnold@canonical.com>

parser/parser_misc.c

@@ -146,6 +146,7 @@ static struct keyword_table keyword_table[] = {
 	{"bind",                TOK_BIND},
 	{"read",                TOK_READ},
 	{"write",               TOK_WRITE},
+	{"eavesdrop",		TOK_EAVESDROP},
 	{"peer",		TOK_PEER},
 
 	/* terminate */