upstream: Add sshd_config CASignatureAlgorithms option to allow

control over which signature algorithms a CA may use when signing
certificates. In particular, this allows a sshd to ban certificates signed
with RSA/SHA1.

ok markus@

OpenBSD-Commit-ID: b05c86ef8b52b913ed48d54a9b9c1a7714d96bac

1 files changed, 13 insertions, 3 deletions

diff --git a/servconf.c b/servconf.c
index c0f6af0be..5411640fc 100644
--- a/servconf.c
+++ b/servconf.c
@@ -1,5 +1,5 @@
 
-/* $OpenBSD: servconf.c,v 1.340 2018/08/12 20:19:13 djm Exp $ */
+/* $OpenBSD: servconf.c,v 1.341 2018/09/20 03:28:06 djm Exp $ */
 /*
  * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
  *                    All rights reserved
@@ -145,6 +145,7 @@ initialize_server_options(ServerOptions *options)
         options->ciphers = NULL;
         options->macs = NULL;
         options->kex_algorithms = NULL;
+        options->ca_sign_algorithms = NULL;
         options->fwd_opts.gateway_ports = -1;
         options->fwd_opts.streamlocal_bind_mask = (mode_t)-1;
         options->fwd_opts.streamlocal_bind_unlink = -1;
@@ -191,13 +192,14 @@ option_clear_or_none(const char *o)
 static void
 assemble_algorithms(ServerOptions *o)
 {
-        char *all_cipher, *all_mac, *all_kex, *all_key;
+        char *all_cipher, *all_mac, *all_kex, *all_key, *all_sig;
         int r;
 
         all_cipher = cipher_alg_list(',', 0);
         all_mac = mac_alg_list(',');
         all_kex = kex_alg_list(',');
         all_key = sshkey_alg_list(0, 0, 1, ',');
+        all_sig = sshkey_alg_list(0, 1, 1, ',');
 #define ASSEMBLE(what, defaults, all) \
         do { \
                 if ((r = kex_assemble_names(&o->what, defaults, all)) != 0) \
@@ -209,11 +211,13 @@ assemble_algorithms(ServerOptions *o)
         ASSEMBLE(hostkeyalgorithms, KEX_DEFAULT_PK_ALG, all_key);
         ASSEMBLE(hostbased_key_types, KEX_DEFAULT_PK_ALG, all_key);
         ASSEMBLE(pubkey_key_types, KEX_DEFAULT_PK_ALG, all_key);
+        ASSEMBLE(ca_sign_algorithms, SSH_ALLOWED_CA_SIGALGS, all_sig);
 #undef ASSEMBLE
         free(all_cipher);
         free(all_mac);
         free(all_kex);
         free(all_key);
+        free(all_sig);
 }
 
 static void
@@ -487,7 +491,7 @@ typedef enum {
         sHostCertificate,
         sRevokedKeys, sTrustedUserCAKeys, sAuthorizedPrincipalsFile,
         sAuthorizedPrincipalsCommand, sAuthorizedPrincipalsCommandUser,
-        sKexAlgorithms, sIPQoS, sVersionAddendum,
+        sKexAlgorithms, sCASignatureAlgorithms, sIPQoS, sVersionAddendum,
         sAuthorizedKeysCommand, sAuthorizedKeysCommandUser,
         sAuthenticationMethods, sHostKeyAgent, sPermitUserRC,
         sStreamLocalBindMask, sStreamLocalBindUnlink,
@@ -1431,6 +1435,10 @@ process_server_config_line(ServerOptions *options, char *line,
                 charptr = &options->hostkeyalgorithms;
                 goto parse_keytypes;
 
+        case sCASignatureAlgorithms:
+                charptr = &options->ca_sign_algorithms;
+                goto parse_keytypes;
+
         case sPubkeyAuthentication:
                 intptr = &options->pubkey_authentication;
                 goto parse_flag;
@@ -2601,6 +2609,8 @@ dump_config(ServerOptions *o)
         dump_cfg_string(sHostKeyAgent, o->host_key_agent);
         dump_cfg_string(sKexAlgorithms,
             o->kex_algorithms ? o->kex_algorithms : KEX_SERVER_KEX);
+        dump_cfg_string(sCASignatureAlgorithms, o->ca_sign_algorithms ?
+            o->ca_sign_algorithms : SSH_ALLOWED_CA_SIGALGS);
         dump_cfg_string(sHostbasedAcceptedKeyTypes, o->hostbased_key_types ?
             o->hostbased_key_types : KEX_DEFAULT_PK_ALG);
         dump_cfg_string(sHostKeyAlgorithms, o->hostkeyalgorithms ?