api request helper: enforce TLS cert-check and add cert-fingerprint option

Currently, we do not verify the TLS certificate for API requests
external IPAM and DNS integration. This could allow man-in-the-middle
attacks, albeit most IPAM infrastructure is on controlled and isolated
LANs, so it's not something that should frequently happen; and
technically our IPAM integration is still marked as tech-preview,
which had its reasons.

Enforce verification, and allow users to pass a cert SHA256
fingerprint to ensure a certificates validity if it's not trusted by
the system trust store, as it's, e.g., the case for self-signed certs.

The code was adapted from the one in pve-apiclient, which we cannot
reuse directly as it is only implemented for requests against PVE
nodes, not as a generic HTTP client request helper.

Add the new dependency `libio-socket-ssl-perl` required to get the
verify callback for the TLS certificate used for cert-fingerprint
checking.

Signed-off-by: Hannes Duerr <h.duerr@proxmox.com>
Tested-by: Stefan Hanreich <s.hanreich@proxmox.com>
 [TL: return valid for non-leaf certs and rewrite commit message]
Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>

1 files changed, 21 insertions, 2 deletions

diff --git a/src/PVE/Network/SDN.pm b/src/PVE/Network/SDN.pm
index 1186d9e..8cd9ad8 100644
--- a/src/PVE/Network/SDN.pm
+++ b/src/PVE/Network/SDN.pm
@@ -3,7 +3,9 @@ package PVE::Network::SDN;
 use strict;
 use warnings;
 
+use IO::Socket::SSL; # important for SSL_verify_callback
 use JSON;
+use Net::SSLeay;
 
 use PVE::INotify;
 
@@ -256,7 +258,7 @@ sub encode_value {
 
 #helpers
 sub api_request {
-    my ($method, $url, $headers, $data) = @_;
+    my ($method, $url, $headers, $data, $expected_fingerprint) = @_;
 
     my $encoded_data = to_json($data) if $data;
 
@@ -270,7 +272,24 @@ sub api_request {
 	$ua->env_proxy;
     }
 
-    $ua->ssl_opts(verify_hostname => 0, SSL_verify_mode => 0x00);
+    if (defined($expected_fingerprint)) {
+	my $ssl_verify_callback = sub {
+	    my (undef, undef, undef, undef, $cert, $depth) = @_;
+
+	    # we don't care about intermediate or root certificates, always return as valid as the
+	    # callback will be executed for all levels and all must be valid.
+	    return 1 if $depth != 0;
+
+	    my $fingerprint = Net::SSLeay::X509_get_fingerprint($cert, 'sha256');
+
+	    return $fingerprint eq $expected_fingerprint ? 1 : 0;
+	};
+	$ua->ssl_opts(
+	    verify_hostname => 0,
+	    SSL_verify_mode => SSL_VERIFY_PEER,
+	    SSL_verify_callback => $ssl_verify_callback,
+	);
+    }
 
     my $response = $ua->request($req);