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, 47 insertions, 0 deletions

diff --git a/servconf.c b/servconf.c
index 70f5f73f0..191575a16 100644
--- a/servconf.c
+++ b/servconf.c
@@ -69,6 +69,7 @@
 #include "auth.h"
 #include "myproposal.h"
 #include "digest.h"
+#include "ssh-gss.h"
 
 static void add_listen_addr(ServerOptions *, const char *,
     const char *, int);
@@ -133,8 +134,11 @@ initialize_server_options(ServerOptions *options)
         options->kerberos_ticket_cleanup = -1;
         options->kerberos_get_afs_token = -1;
         options->gss_authentication=-1;
+        options->gss_keyex = -1;
         options->gss_cleanup_creds = -1;
         options->gss_strict_acceptor = -1;
+        options->gss_store_rekey = -1;
+        options->gss_kex_algorithms = NULL;
         options->password_authentication = -1;
         options->kbd_interactive_authentication = -1;
         options->challenge_response_authentication = -1;
@@ -375,10 +379,18 @@ fill_default_server_options(ServerOptions *options)
                 options->kerberos_get_afs_token = 0;
         if (options->gss_authentication == -1)
                 options->gss_authentication = 0;
+        if (options->gss_keyex == -1)
+                options->gss_keyex = 0;
         if (options->gss_cleanup_creds == -1)
                 options->gss_cleanup_creds = 1;
         if (options->gss_strict_acceptor == -1)
                 options->gss_strict_acceptor = 1;
+        if (options->gss_store_rekey == -1)
+                options->gss_store_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)
@@ -531,6 +543,7 @@ typedef enum {
         sHostKeyAlgorithms,
         sClientAliveInterval, sClientAliveCountMax, sAuthorizedKeysFile,
         sGssAuthentication, sGssCleanupCreds, sGssStrictAcceptor,
+        sGssKeyEx, sGssKexAlgorithms, sGssStoreRekey,
         sAcceptEnv, sSetEnv, sPermitTunnel,
         sMatch, sPermitOpen, sPermitListen, sForceCommand, sChrootDirectory,
         sUsePrivilegeSeparation, sAllowAgentForwarding,
@@ -607,12 +620,22 @@ static struct {
 #ifdef GSSAPI
         { "gssapiauthentication", sGssAuthentication, SSHCFG_ALL },
         { "gssapicleanupcredentials", sGssCleanupCreds, SSHCFG_GLOBAL },
+        { "gssapicleanupcreds", sGssCleanupCreds, SSHCFG_GLOBAL },
         { "gssapistrictacceptorcheck", sGssStrictAcceptor, SSHCFG_GLOBAL },
+        { "gssapikeyexchange", sGssKeyEx, SSHCFG_GLOBAL },
+        { "gssapistorecredentialsonrekey", sGssStoreRekey, SSHCFG_GLOBAL },
+        { "gssapikexalgorithms", sGssKexAlgorithms, SSHCFG_GLOBAL },
 #else
         { "gssapiauthentication", sUnsupported, SSHCFG_ALL },
         { "gssapicleanupcredentials", sUnsupported, SSHCFG_GLOBAL },
+        { "gssapicleanupcreds", sUnsupported, SSHCFG_GLOBAL },
         { "gssapistrictacceptorcheck", sUnsupported, SSHCFG_GLOBAL },
+        { "gssapikeyexchange", sUnsupported, SSHCFG_GLOBAL },
+        { "gssapistorecredentialsonrekey", sUnsupported, SSHCFG_GLOBAL },
+        { "gssapikexalgorithms", sUnsupported, SSHCFG_GLOBAL },
 #endif
+        { "gssusesessionccache", sUnsupported, SSHCFG_GLOBAL },
+        { "gssapiusesessioncredcache", sUnsupported, SSHCFG_GLOBAL },
         { "passwordauthentication", sPasswordAuthentication, SSHCFG_ALL },
         { "kbdinteractiveauthentication", sKbdInteractiveAuthentication, SSHCFG_ALL },
         { "challengeresponseauthentication", sChallengeResponseAuthentication, SSHCFG_GLOBAL },
@@ -1548,6 +1571,10 @@ process_server_config_line_depth(ServerOptions *options, char *line,
                 intptr = &options->gss_authentication;
                 goto parse_flag;
 
+        case sGssKeyEx:
+                intptr = &options->gss_keyex;
+                goto parse_flag;
+
         case sGssCleanupCreds:
                 intptr = &options->gss_cleanup_creds;
                 goto parse_flag;
@@ -1556,6 +1583,22 @@ process_server_config_line_depth(ServerOptions *options, char *line,
                 intptr = &options->gss_strict_acceptor;
                 goto parse_flag;
 
+        case sGssStoreRekey:
+                intptr = &options->gss_store_rekey;
+                goto parse_flag;
+
+        case sGssKexAlgorithms:
+                arg = strdelim(&cp);
+                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 sPasswordAuthentication:
                 intptr = &options->password_authentication;
                 goto parse_flag;
@@ -2777,6 +2820,10 @@ dump_config(ServerOptions *o)
 #ifdef GSSAPI
         dump_cfg_fmtint(sGssAuthentication, o->gss_authentication);
         dump_cfg_fmtint(sGssCleanupCreds, o->gss_cleanup_creds);
+        dump_cfg_fmtint(sGssKeyEx, o->gss_keyex);
+        dump_cfg_fmtint(sGssStrictAcceptor, o->gss_strict_acceptor);
+        dump_cfg_fmtint(sGssStoreRekey, o->gss_store_rekey);
+        dump_cfg_string(sGssKexAlgorithms, o->gss_kex_algorithms);
 #endif
         dump_cfg_fmtint(sPasswordAuthentication, o->password_authentication);
         dump_cfg_fmtint(sKbdInteractiveAuthentication,