[PATCH 3/3] nntp: fix handling of trickled responses

[Eric Wong <e@80x24.org>]

We cannot use the push_back_read functionality of Danga::Socket
since it will trigger event_read on buffered data.  This would
allow a malicious (or badly implemented) client to burn CPU
without actually sending us anything.

So we still do buffering ourselves and play some tricks with
timers re-enable readability.
---
 lib/PublicInbox/NNTP.pm | 37 +++++++++++++++++++++++++++++++------
 public-inbox-nntpd      |  3 ++-
 2 files changed, 33 insertions(+), 7 deletions(-)

diff --git a/lib/PublicInbox/NNTP.pm b/lib/PublicInbox/NNTP.pm
index 0e91082..8f86685 100644
--- a/lib/PublicInbox/NNTP.pm
+++ b/lib/PublicInbox/NNTP.pm
@@ -4,7 +4,7 @@ package PublicInbox::NNTP;
 use strict;
 use warnings;
 use base qw(Danga::Socket);
-use fields qw(nntpd article ng long_res);
+use fields qw(nntpd article rbuf ng long_res);
 use PublicInbox::Msgmap;
 use PublicInbox::GitCatFile;
 use PublicInbox::MID qw(mid2path);
@@ -32,6 +32,7 @@ sub new ($$$) {
 	$self->SUPER::new($sock);
 	$self->{nntpd} = $nntpd;
 	res($self, '201 server ready - post via email');
+	$self->{rbuf} = '';
 	$self->watch_read(1);
 	$self;
 }
@@ -762,20 +763,44 @@ sub event_write {
 sub event_read {
 	my ($self) = @_;
 	use constant LINE_MAX => 512; # RFC 977 section 2.3
+	my $line;
 	my $r = 1;
-	my $buf = $self->read(LINE_MAX) or return $self->close;
-	while ($r > 0 && $$buf =~ s/\A\s*([^\r\n]+)\r?\n//) {
-		my $line = $1;
+again:
+	while ($r > 0 && $self->{rbuf} =~ s/\A\s*([^\r\n]+)\r?\n//) {
+		$line = $1;
 		my $t0 = now();
 		$r = eval { $self->process_line($line) };
 		my $d = $self->{long_res} ?
 			' deferred['.fileno($self->{sock}).']' : '';
 		out($self, "$line - %0.6f$d", now() - $t0);
 	}
+	unless (defined $line) {
+		my $buf = $self->read(LINE_MAX) or return $self->close;
+		$self->{rbuf} .= $$buf;
+		goto again;
+	}
+
 	return $self->close if $r < 0;
-	my $len = bytes::length($$buf);
+	my $len = bytes::length($self->{rbuf});
 	return $self->close if ($len >= LINE_MAX);
-	$self->push_back_read($buf) if ($len);
+}
+
+sub watch_read {
+	my ($self, $bool) = @_;
+	my $rv = $self->SUPER::watch_read($bool);
+	if ($bool && $self->{rbuf} ne '') {
+		# Force another read if there is a pipelined request.
+		# We don't know if the socket has anything for us to read,
+		# and we must double-check again by the time the timer fires
+		# in case we really did dispatch a read event and started
+		# another long response.
+		Danga::Socket->AddTimer(0, sub {
+			if (&Danga::Socket::POLLIN & $self->{event_watch}) {
+				$self->event_read;
+			}
+		});
+	}
+	$rv;
 }
 
 1;
diff --git a/public-inbox-nntpd b/public-inbox-nntpd
index 588efdd..b66de58 100644
--- a/public-inbox-nntpd
+++ b/public-inbox-nntpd
@@ -146,7 +146,8 @@ sub worker_quit {
 		my ($dmap, undef) = @_;
 		my $n = 0;
 		foreach my $s (values %$dmap) {
-			if ($s->{write_buf_size} || @{$s->{read_push_back}}) {
+			next unless ref($s) eq 'PublicInbox::NNTP';
+			if ($s->{write_buf_size} || $s->{rbuf}) {
 				++$n;
 			} else {
 				$s->close;
-- 
EW