AST-2014-017 - app_confbridge: permission escalation/ class authorization.

AST-2014-017 - app_confbridge: permission escalation/ class authorization.

Confbridge dialplan function permission escalation via AMI and inappropriate
class authorization on the ConfbridgeStartRecord action. The CONFBRIDGE dialplan
function when executed from an external protocol (for instance AMI), could
result in a privilege escalation. Also, the AMI action “ConfbridgeStartRecord”
could also be used to execute arbitrary system commands without first checking
for system access.

Asterisk now inhibits the CONFBRIDGE function from being executed from an
external interface if the live_dangerously option is set to no.  Also, the
“ConfbridgeStartRecord” AMI action is now only allowed to execute under a
user with system level access.

ASTERISK-24490
Reported by: Gareth Palmer

git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/11@428332 65c4cc65-6c06-0410-ace0-fbb531ad65f3