[pve-devel] [PATCH http-server] fix #3724: disable TLS renegotiation

[Stoiko Ivanov]

The issue is probably not critical and best addressed by not running
the perl API servers in an exposed environment or when this needs to
be done by installing a reverse proxy in front of them.

The DOS potential of the perl daemons is limited more by the limited
number of parallel workers (and the memory constraints of starting
more of them), than by the CPU cycles wasted on TLS renegotiation.

Still disabling TLS renegotiation should show very little downside:
* it was removed in TLS 1.3 for security reasons
* it was the way nginx addressed this issue [1].
* we do not use client certificate authentication

Tested by running `openssl s_client -no_tls1_3 -connect 192.0.2.1:8006`
and issuing a `HEAD / HTTP/1.1\nR\n`
with and without the patch.

[1] 70bd187c4c386d82d6e4d180e0db84f361d1be02 at
    https://github.com/nginx/nginx (although that code adapted to
    the various changes in openssl API over the years)
Signed-off-by: Stoiko Ivanov <s.ivanov at proxmox.com>
---
 src/PVE/APIServer/AnyEvent.pm | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/src/PVE/APIServer/AnyEvent.pm b/src/PVE/APIServer/AnyEvent.pm
index 86d0e2e..e3633f7 100644
--- a/src/PVE/APIServer/AnyEvent.pm
+++ b/src/PVE/APIServer/AnyEvent.pm
@@ -1883,7 +1883,8 @@ sub new {
 	    $self->{ssl}->{dh} = 'skip2048';
 	}
 
-	my $tls_ctx_flags = &Net::SSLeay::OP_NO_COMPRESSION | &Net::SSLeay::OP_SINGLE_ECDH_USE | &Net::SSLeay::OP_SINGLE_DH_USE;
+	my $tls_ctx_flags = &Net::SSLeay::OP_NO_COMPRESSION | &Net::SSLeay::OP_SINGLE_ECDH_USE |
+	    &Net::SSLeay::OP_SINGLE_DH_USE | &Net::SSLeay::OP_NO_RENEGOTIATION;
 	if ( delete $self->{ssl}->{honor_cipher_order} ) {
 	    $tls_ctx_flags |= &Net::SSLeay::OP_CIPHER_SERVER_PREFERENCE;
 	}
-- 
2.30.2