GSSAPI key exchange support

This patch has been rejected upstream: "None of the OpenSSH developers are
in favour of adding this, and this situation has not changed for several
years.  This is not a slight on Simon's patch, which is of fine quality, but
just that a) we don't trust GSSAPI implementations that much and b) we don't
like adding new KEX since they are pre-auth attack surface.  This one is
particularly scary, since it requires hooks out to typically root-owned
system resources."

However, quite a lot of people rely on this in Debian, and it's better to
have it merged into the main openssh package rather than having separate
-krb5 packages (as we used to have).  It seems to have a generally good
security history.

Origin: other, https://github.com/openssh-gsskex/openssh-gsskex/commits/debian/master
Bug: https://bugzilla.mindrot.org/show_bug.cgi?id=1242
Last-Updated: 2020-02-21

Patch-Name: gssapi.patch

1 files changed, 70 insertions, 0 deletions

diff --git a/readconf.c b/readconf.c
index f3cac6b3a..da8022dd0 100644
--- a/readconf.c
+++ b/readconf.c
@@ -67,6 +67,7 @@
 #include "uidswap.h"
 #include "myproposal.h"
 #include "digest.h"
+#include "ssh-gss.h"
 
 /* Format of the configuration file:
 
@@ -160,6 +161,8 @@ typedef enum {
         oClearAllForwardings, oNoHostAuthenticationForLocalhost,
         oEnableSSHKeysign, oRekeyLimit, oVerifyHostKeyDNS, oConnectTimeout,
         oAddressFamily, oGssAuthentication, oGssDelegateCreds,
+        oGssTrustDns, oGssKeyEx, oGssClientIdentity, oGssRenewalRekey,
+        oGssServerIdentity, oGssKexAlgorithms,
         oServerAliveInterval, oServerAliveCountMax, oIdentitiesOnly,
         oSendEnv, oSetEnv, oControlPath, oControlMaster, oControlPersist,
         oHashKnownHosts,
@@ -204,10 +207,22 @@ static struct {
         /* Sometimes-unsupported options */
 #if defined(GSSAPI)
         { "gssapiauthentication", oGssAuthentication },
+        { "gssapikeyexchange", oGssKeyEx },
         { "gssapidelegatecredentials", oGssDelegateCreds },
+        { "gssapitrustdns", oGssTrustDns },
+        { "gssapiclientidentity", oGssClientIdentity },
+        { "gssapiserveridentity", oGssServerIdentity },
+        { "gssapirenewalforcesrekey", oGssRenewalRekey },
+        { "gssapikexalgorithms", oGssKexAlgorithms },
 # else
         { "gssapiauthentication", oUnsupported },
+        { "gssapikeyexchange", oUnsupported },
         { "gssapidelegatecredentials", oUnsupported },
+        { "gssapitrustdns", oUnsupported },
+        { "gssapiclientidentity", oUnsupported },
+        { "gssapiserveridentity", oUnsupported },
+        { "gssapirenewalforcesrekey", oUnsupported },
+        { "gssapikexalgorithms", oUnsupported },
 #endif
 #ifdef ENABLE_PKCS11
         { "pkcs11provider", oPKCS11Provider },
@@ -1029,10 +1044,42 @@ parse_time:
                 intptr = &options->gss_authentication;
                 goto parse_flag;
 
+        case oGssKeyEx:
+                intptr = &options->gss_keyex;
+                goto parse_flag;
+
         case oGssDelegateCreds:
                 intptr = &options->gss_deleg_creds;
                 goto parse_flag;
 
+        case oGssTrustDns:
+                intptr = &options->gss_trust_dns;
+                goto parse_flag;
+
+        case oGssClientIdentity:
+                charptr = &options->gss_client_identity;
+                goto parse_string;
+
+        case oGssServerIdentity:
+                charptr = &options->gss_server_identity;
+                goto parse_string;
+
+        case oGssRenewalRekey:
+                intptr = &options->gss_renewal_rekey;
+                goto parse_flag;
+
+        case oGssKexAlgorithms:
+                arg = strdelim(&s);
+                if (!arg || *arg == '\0')
+                        fatal("%.200s line %d: Missing argument.",
+                            filename, linenum);
+                if (!kex_gss_names_valid(arg))
+                        fatal("%.200s line %d: Bad GSSAPI KexAlgorithms '%s'.",
+                            filename, linenum, arg ? arg : "<NONE>");
+                if (*activep && options->gss_kex_algorithms == NULL)
+                        options->gss_kex_algorithms = xstrdup(arg);
+                break;
+
         case oBatchMode:
                 intptr = &options->batch_mode;
                 goto parse_flag;
@@ -1911,7 +1958,13 @@ initialize_options(Options * options)
         options->pubkey_authentication = -1;
         options->challenge_response_authentication = -1;
         options->gss_authentication = -1;
+        options->gss_keyex = -1;
         options->gss_deleg_creds = -1;
+        options->gss_trust_dns = -1;
+        options->gss_renewal_rekey = -1;
+        options->gss_client_identity = NULL;
+        options->gss_server_identity = NULL;
+        options->gss_kex_algorithms = NULL;
         options->password_authentication = -1;
         options->kbd_interactive_authentication = -1;
         options->kbd_interactive_devices = NULL;
@@ -2059,8 +2112,18 @@ fill_default_options(Options * options)
                 options->challenge_response_authentication = 1;
         if (options->gss_authentication == -1)
                 options->gss_authentication = 0;
+        if (options->gss_keyex == -1)
+                options->gss_keyex = 0;
         if (options->gss_deleg_creds == -1)
                 options->gss_deleg_creds = 0;
+        if (options->gss_trust_dns == -1)
+                options->gss_trust_dns = 0;
+        if (options->gss_renewal_rekey == -1)
+                options->gss_renewal_rekey = 0;
+#ifdef GSSAPI
+        if (options->gss_kex_algorithms == NULL)
+                options->gss_kex_algorithms = strdup(GSS_KEX_DEFAULT_KEX);
+#endif
         if (options->password_authentication == -1)
                 options->password_authentication = 1;
         if (options->kbd_interactive_authentication == -1)
@@ -2702,7 +2765,14 @@ dump_client_config(Options *o, const char *host)
         dump_cfg_fmtint(oGatewayPorts, o->fwd_opts.gateway_ports);
 #ifdef GSSAPI
         dump_cfg_fmtint(oGssAuthentication, o->gss_authentication);
+        dump_cfg_fmtint(oGssKeyEx, o->gss_keyex);
         dump_cfg_fmtint(oGssDelegateCreds, o->gss_deleg_creds);
+        dump_cfg_fmtint(oGssTrustDns, o->gss_trust_dns);
+        dump_cfg_fmtint(oGssRenewalRekey, o->gss_renewal_rekey);
+        dump_cfg_string(oGssClientIdentity, o->gss_client_identity);
+        dump_cfg_string(oGssServerIdentity, o->gss_server_identity);
+        dump_cfg_string(oGssKexAlgorithms, o->gss_kex_algorithms ?
+            o->gss_kex_algorithms : GSS_KEX_DEFAULT_KEX);
 #endif /* GSSAPI */
         dump_cfg_fmtint(oHashKnownHosts, o->hash_known_hosts);
         dump_cfg_fmtint(oHostbasedAuthentication, o->hostbased_authentication);