zeek/scripts/policy/protocols/dns/detect-external-names.zeek
Benjamin Bannier d5fd29edcd Prefer explicit construction to coercion in record initialization
While we support initializing records via coercion from an expression
list, e.g.,

    local x: X = [$x1=1, $x2=2];

this can sometimes obscure the code to readers, e.g., when assigning to
value declared and typed elsewhere. The language runtime has a similar
overhead since instead of just constructing a known type it needs to
check at runtime that the coercion from the expression list is valid;
this can be slower than just writing the readible code in the first
place, see #4559.

With this patch we use explicit construction, e.g.,

    local x = X($x1=1, $x2=2);
2025-07-11 16:28:37 -07:00

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1.6 KiB
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##! This script detects names which are not within zones considered to be
##! local but resolving to addresses considered local.
##! The :zeek:id:`Site::local_zones` variable **must** be set appropriately for
##! this detection.
@load base/frameworks/notice
@load base/utils/site
module DNS;
export {
redef enum Notice::Type += {
## Raised when a non-local name is found to be pointing at a
## local host. The :zeek:id:`Site::local_zones` variable
## **must** be set appropriately for this detection.
External_Name,
};
## Default is to ignore mDNS broadcasts.
option skip_resp_host_port_pairs: set[addr, port] = { [[224.0.0.251, [ff02::fb]], 5353/udp] };
}
function detect_external_names(c: connection, msg: dns_msg, ans: dns_answer, a: addr)
{
if ( |Site::local_zones| == 0 )
return;
if ( [c$id$resp_h, c$id$resp_p] in skip_resp_host_port_pairs )
return;
# Check for responses from remote hosts that point at local hosts
# but the name is not considered to be within a "local" zone.
if ( Site::is_local_addr(a) && # referring to a local host
! Site::is_local_name(ans$query) ) # name isn't in a local zone.
{
NOTICE(Notice::Info($note=External_Name,
$msg=fmt("%s is pointing to a local host - %s.", ans$query, a),
$conn=c,
$identifier=cat(a,ans$query)));
}
}
event dns_A_reply(c: connection, msg: dns_msg, ans: dns_answer, a: addr)
{
detect_external_names(c, msg, ans, a);
}
event dns_AAAA_reply(c: connection, msg: dns_msg, ans: dns_answer, a: addr)
{
detect_external_names(c, msg, ans, a);
}