A user reported being confused about the fuid association of subsequent
FTP commands when a data transfer has completed. It seems reasonable to
unset fuid upon logging a FTP command which had a fuid.
The current behavior results in the PORT or PASV commands after a RETR or STOR
to have the fuid of the prior file transfer. Similarly, any CWD or DEL commands
following a file transfer will unnecessarily be logged with the fuid of the
prior file transfer.
This tickles the baselines for the private testing PCAP a lot, primarily
because there data connections in that pcap are never established properly.
E.g, the fuids FzDzid1Dxm9srVKHXf and FEfYX73q5C6GEQZXX9 have been re-used
for multiple commands.
This may look like we're losing information, but the fuids vanishing
in the normal btests belong to a LIST command that isn't logged by
default into ftp.log. If it was, the fuid would be attached to it.
Previously, seq was computed as the result of |pending_commands|+1. This
opened the possibility to override queued commands, as well as logging
the same pending ftp reply multiple times.
For example, when commands 1, 2, 3 are pending, command 1 may be dequeued,
but the incoming command then receives seq 3 and overrides the already
pending command 3. The second scenario happens when ftp_reply() selected
command 3 as pending for logging, but is then followed by many ftp_request()
events. This resulted in command 3's response being logged for every
following ftp_request() over and over again.
Avoid both scenarios by tracking the command sequence as an absolute counter.
OSS Fuzz generated a CWD request and reply followed by very many EPRT
requests. This caused Zeek to re-log the CWD request and invoke `build_url_ftp()`
over and over again resulting in long processing times.
Avoid this scenario by not logging commands that aren't pending anymore.
(cherry picked from commit b05dd31667ff634ec7d017f09d122f05878fdf65)
OSS-Fuzz generated traffic containing a CWD command with a single very large
path argument (427kb) starting with ".___/` \x00\x00...", This is followed
by a large number of ftp replies with code 250. The directory logic in
ftp_reply() would match every incoming reply with the one pending CWD command,
triggering path buildup ending with something 120MB in size.
Protect from re-using a directory command by setting a flag in the
CmdArg record when it was consumed for the path traversal logic.
This doesn't prevent unbounded path build-up generally, but does prevent the
amplification of a single large command with very many small ftp_replies.
Re-using a pending path command seems like a bug as well.
The medium.trace in the private external test suite contains one
session/server that violates the multi-line reply protocol and
happened to work out fairly well regardless due to how we looked
up the pending commands unconditionally before.
Continue to match up reply lines that "look like they contain status codes"
even if cont_resp = T. This still improves runtime for the OSS-Fuzz
generated test case and keeps the external baselines valid.
The affected session can be extracted as follows:
zcat Traces/medium.trace.gz | tcpdump -r - 'port 1491 and port 21'
We could push this into the analyzer, too, minimally the RFC says:
> If an intermediary line begins with a 3-digit number, the Server
> must pad the front to avoid confusion.
Intermediate lines of multiline replies usually do not contain valid status
codes (even if servers may opt to include them). Their content may be anything
and likely unrelated to the original command. There's little reason for us
trying to match them with a corresponding command.
OSS-Fuzz generated a large command reply with very many intermediate lines
which caused long processing times due to matching every line with all
currently pending commands.
This is a DoS vector against Zeek. The new ipv6-multiline-reply.trace and
ipv6-retr-samba.trace files have been extracted from the external ipv6.trace.
The user and password fields are replicated to each of the ftp.log
entries. Using a very large username (100s of KBs) allows to bloat
the log without actually sending much traffic. Further, limit the
arg and reply_msg columns to large, but not unbounded values.
This adds a "policy" hook into the logging framework's streams and
filters to replace the existing log filter predicates. The hook
signature is as follows:
hook(rec: any, id: Log::ID, filter: Log::Filter);
The logging manager invokes hooks on each log record. Hooks can veto
log records via a break, and modify them if necessary. Log filters
inherit the stream-level hook, but can override or remove the hook as
needed.
The distribution's existing log streams now come with pre-defined
hooks that users can add handlers to. Their name is standardized as
"log_policy" by convention, with additional suffixes when a module
provides multiple streams. The following adds a handler to the Conn
module's default log policy hook:
hook Conn::log_policy(rec: Conn::Info, id: Log::ID, filter: Log::Filter)
{
if ( some_veto_reason(rec) )
break;
}
By default, this handler will get invoked for any log filter
associated with the Conn::LOG stream.
The existing predicates are deprecated for removal in 4.1 but continue
to work.
This adds two new functions: `Conn::register_removal_hook()` and
`Conn::unregister_removal_hook()` for registering a hook function to be
called back during `connection_state_remove`. The benefit of using hook
callback approach is better scalability: the overhead of unrelated
protocols having to dispatch no-op `connection_state_remove` handlers is
avoided.
Previously, more data than could effectively be utilized by any remote
Zeek was published (e.g. full list of pending commands or other
transient state that may add up to non-trivial amount of bytes).
And switch Zeek's base scripts over to using it in place of
"connection_state_remove". The difference between the two is
that "connection_state_remove" is raised for all events while
"successful_connection_remove" excludes TCP connections that were never
established (just SYN packets). There can be performance benefits
to this change for some use-cases.
There's also a new event called ``connection_successful`` and a new
``connection`` record field named "successful" to help indicate this new
property of connections.
Minor cleanup in merge: remove print statements and unnecessary @if
directive.
* 'topic/jsbarber/ftp-cluster-fix-patch' of https://github.com/jsbarber/zeek:
Publish ftp_data_expected updates to other workers for synchronization
* All "Broxygen" usages have been replaced in
code, documentation, filenames, etc.
* Sphinx roles/directives like ":bro:see" are now ":zeek:see"
* The "--broxygen" command-line option is now "--zeexygen"
