When disabling_analyzer() was introduced, it was added to the GLOBAL
module. The awkward side-effect is that implementing a hook handler
in another module requires to prefix it with GLOBAL. Alternatively, one
can re-open the GLOBAL module and implement the handler in that scope.
Both are not great, and prefixing with GLOBAL is ugly, so move the
identifier to the Analyzer module and ask users to prefix with Analyzer.
This hook can be used to coordinate disabling an analyzer for a given
connection. The contract is simple: Any script can veto a disable_analyzer()
call by breaking from this hook. The decision is local to the script taking
into account any state attached to the connection object or script specific
state stored elsewhere.
A script breaking from the hook takes over the responsibility to call
disable_analyzer() at a later point when it finds the condition due to which
it vetoed fulfilled (which may be never).
Signature:
disabling_analyzer: hook(c: connection, atype: AllAnalyzers::Tag, aid: count);
Example use-cases are keeping the SSL analyzer enabled for finger-printing
until a certain amount of bytes or packets have been transferred or
similarly the connection duration exceed a certain threshold.
Other example use-cases might be keeping analyzers for SSH, RDP or SSL
enabled for connections from specific subnets.
It's a bit quirky as it makes disable_analyzer() a maybe operation. While log
policy hooks and/or the notice hook have similar semantics, they are not as
stateful. It still seems like a quite powerful primitive.
The disable_analyzer() call in dpd/main.zeek may motivate the addition of a
force flag as a follow-up for situations where the caller "knows better" or
absolutely wants to override.
Closes#1678#1593.
