forked from rpms/openssh
290 lines
14 KiB
Diff
290 lines
14 KiB
Diff
diff -up openssh-7.4p1/auth-krb5.c.kuserok openssh-7.4p1/auth-krb5.c
|
|
--- openssh-7.4p1/auth-krb5.c.kuserok 2016-12-23 14:36:07.640465939 +0100
|
|
+++ openssh-7.4p1/auth-krb5.c 2016-12-23 14:36:07.644465936 +0100
|
|
@@ -56,6 +56,21 @@
|
|
|
|
extern ServerOptions options;
|
|
|
|
+int
|
|
+ssh_krb5_kuserok(krb5_context krb5_ctx, krb5_principal krb5_user, const char *client,
|
|
+ int k5login_exists)
|
|
+{
|
|
+ if (options.use_kuserok || !k5login_exists)
|
|
+ return krb5_kuserok(krb5_ctx, krb5_user, client);
|
|
+ else {
|
|
+ char kuser[65];
|
|
+
|
|
+ if (krb5_aname_to_localname(krb5_ctx, krb5_user, sizeof(kuser), kuser))
|
|
+ return 0;
|
|
+ return strcmp(kuser, client) == 0;
|
|
+ }
|
|
+}
|
|
+
|
|
static int
|
|
krb5_init(void *context)
|
|
{
|
|
@@ -160,8 +175,9 @@ auth_krb5_password(Authctxt *authctxt, c
|
|
if (problem)
|
|
goto out;
|
|
|
|
- if (!krb5_kuserok(authctxt->krb5_ctx, authctxt->krb5_user,
|
|
- authctxt->pw->pw_name)) {
|
|
+ /* Use !options.use_kuserok here to make ssh_krb5_kuserok() not
|
|
+ * depend on the existance of .k5login */
|
|
+ if (!ssh_krb5_kuserok(authctxt->krb5_ctx, authctxt->krb5_user, authctxt->pw->pw_name, !options.use_kuserok)) {
|
|
problem = -1;
|
|
goto out;
|
|
}
|
|
diff -up openssh-7.4p1/gss-serv-krb5.c.kuserok openssh-7.4p1/gss-serv-krb5.c
|
|
--- openssh-7.4p1/gss-serv-krb5.c.kuserok 2016-12-23 14:36:07.640465939 +0100
|
|
+++ openssh-7.4p1/gss-serv-krb5.c 2016-12-23 14:36:07.644465936 +0100
|
|
@@ -67,6 +67,7 @@ static int ssh_gssapi_krb5_cmdok(krb5_pr
|
|
int);
|
|
|
|
static krb5_context krb_context = NULL;
|
|
+extern int ssh_krb5_kuserok(krb5_context, krb5_principal, const char *, int);
|
|
|
|
/* Initialise the krb5 library, for the stuff that GSSAPI won't do */
|
|
|
|
@@ -92,6 +93,103 @@ ssh_gssapi_krb5_init(void)
|
|
* Returns true if the user is OK to log in, otherwise returns 0
|
|
*/
|
|
|
|
+/* The purpose of the function is to find out if a Kerberos principal is
|
|
+ * allowed to log in as the given local user. This is a general problem with
|
|
+ * Kerberized services because by design the Kerberos principals are
|
|
+ * completely independent from the local user names. This is one of the
|
|
+ * reasons why Kerberos is working well on different operating systems like
|
|
+ * Windows and UNIX/Linux. Nevertheless a relationship between a Kerberos
|
|
+ * principal and a local user name must be established because otherwise every
|
|
+ * access would be granted for every principal with a valid ticket.
|
|
+ *
|
|
+ * Since it is a general issue libkrb5 provides some functions for
|
|
+ * applications to find out about the relationship between the Kerberos
|
|
+ * principal and a local user name. They are krb5_kuserok() and
|
|
+ * krb5_aname_to_localname().
|
|
+ *
|
|
+ * krb5_kuserok() can be used to "Determine if a principal is authorized to
|
|
+ * log in as a local user" (from the MIT Kerberos documentation of this
|
|
+ * function). Which is exactly what we are looking for and should be the
|
|
+ * preferred choice. It accepts the Kerberos principal and a local user name
|
|
+ * and let libkrb5 or its plugins determine if they relate to each other or
|
|
+ * not.
|
|
+ *
|
|
+ * krb5_aname_to_localname() can use used to "Convert a principal name to a
|
|
+ * local name" (from the MIT Kerberos documentation of this function). It
|
|
+ * accepts a Kerberos principle and returns a local name and it is up to the
|
|
+ * application to do any additional checks. There are two issues using
|
|
+ * krb5_aname_to_localname(). First, since POSIX user names are case
|
|
+ * sensitive, the calling application in general has no other choice than
|
|
+ * doing a case-sensitive string comparison between the name returned by
|
|
+ * krb5_aname_to_localname() and the name used at the login prompt. When the
|
|
+ * users are provided by a case in-sensitive server, e.g. Active Directory,
|
|
+ * this might lead to login failures because the user typing the name at the
|
|
+ * login prompt might not be aware of the right case. Another issue might be
|
|
+ * caused if there are multiple alias names available for a single user. E.g.
|
|
+ * the canonical name of a user is user@group.department.example.com but there
|
|
+ * exists a shorter login name, e.g. user@example.com, to safe typing at the
|
|
+ * login prompt. Here krb5_aname_to_localname() can only return the canonical
|
|
+ * name, but if the short alias is used at the login prompt authentication
|
|
+ * will fail as well. All this can be avoided by using krb5_kuserok() and
|
|
+ * configuring krb5.conf or using a suitable plugin to meet the needs of the
|
|
+ * given environment.
|
|
+ *
|
|
+ * The Fedora and RHEL version of openssh contain two patches which modify the
|
|
+ * access control behavior:
|
|
+ * - openssh-6.6p1-kuserok.patch
|
|
+ * - openssh-6.6p1-force_krb.patch
|
|
+ *
|
|
+ * openssh-6.6p1-kuserok.patch adds a new option KerberosUseKuserok for
|
|
+ * sshd_config which controls if krb5_kuserok() is used to check if the
|
|
+ * principle is authorized or if krb5_aname_to_localname() should be used.
|
|
+ * The reason to add this patch was that krb5_kuserok() by default checks if
|
|
+ * a .k5login file exits in the users home-directory. With this the user can
|
|
+ * give access to his account for any given principal which might be
|
|
+ * in violation with company policies and it would be useful if this can be
|
|
+ * rejected. Nevertheless the patch ignores the fact that krb5_kuserok() does
|
|
+ * no only check .k5login but other sources as well and checking .k5login can
|
|
+ * be disabled for all applications in krb5.conf as well. With this new
|
|
+ * option KerberosUseKuserok set to 'no' (and this is the default for RHEL7
|
|
+ * and Fedora 21) openssh can only use krb5_aname_to_localname() with the
|
|
+ * restrictions mentioned above.
|
|
+ *
|
|
+ * openssh-6.6p1-force_krb.patch adds a ksu like behaviour to ssh, i.e. when
|
|
+ * using GSSAPI authentication only commands configured in the .k5user can be
|
|
+ * executed. Here the wrong assumption that krb5_kuserok() only checks
|
|
+ * .k5login is made as well. In contrast ksu checks .k5login directly and
|
|
+ * does not use krb5_kuserok() which might be more useful for the given
|
|
+ * purpose. Additionally this patch is not synced with
|
|
+ * openssh-6.6p1-kuserok.patch.
|
|
+ *
|
|
+ * The current patch tries to restore the usage of krb5_kuserok() so that e.g.
|
|
+ * localauth plugins can be used. It does so by adding a forth parameter to
|
|
+ * ssh_krb5_kuserok() which indicates whether .k5login exists or not. If it
|
|
+ * does not exists krb5_kuserok() is called even if KerberosUseKuserok is set
|
|
+ * to 'no' because the intent of the option is to not check .k5login and if it
|
|
+ * does not exists krb5_kuserok() returns a result without checking .k5login.
|
|
+ * If .k5login does exists and KerberosUseKuserok is 'no' we fall back to
|
|
+ * krb5_aname_to_localname(). This is in my point of view an acceptable
|
|
+ * limitation and does not break the current behaviour.
|
|
+ *
|
|
+ * Additionally with this patch ssh_krb5_kuserok() is called in
|
|
+ * ssh_gssapi_krb5_cmdok() instead of only krb5_aname_to_localname() is
|
|
+ * neither .k5login nor .k5users exists to allow plugin evaluation via
|
|
+ * krb5_kuserok() as well.
|
|
+ *
|
|
+ * I tried to keep the patch as minimal as possible, nevertheless I see some
|
|
+ * areas for improvement which, if they make sense, have to be evaluated
|
|
+ * carefully because they might change existing behaviour and cause breaks
|
|
+ * during upgrade:
|
|
+ * - I wonder if disabling .k5login usage make sense in sshd or if it should
|
|
+ * be better disabled globally in krb5.conf
|
|
+ * - if really needed openssh-6.6p1-kuserok.patch should be fixed to really
|
|
+ * only disable checking .k5login and maybe .k5users
|
|
+ * - the ksu behaviour should be configurable and maybe check the .k5login and
|
|
+ * .k5users files directly like ksu itself does
|
|
+ * - to make krb5_aname_to_localname() more useful an option for sshd to use
|
|
+ * the canonical name (the one returned by getpwnam()) instead of the name
|
|
+ * given at the login prompt might be useful */
|
|
+
|
|
static int
|
|
ssh_gssapi_krb5_userok(ssh_gssapi_client *client, char *name)
|
|
{
|
|
@@ -116,7 +214,8 @@ ssh_gssapi_krb5_userok(ssh_gssapi_client
|
|
/* NOTE: .k5login and .k5users must opened as root, not the user,
|
|
* because if they are on a krb5-protected filesystem, user credentials
|
|
* to access these files aren't available yet. */
|
|
- if (krb5_kuserok(krb_context, princ, name) && k5login_exists) {
|
|
+ if (ssh_krb5_kuserok(krb_context, princ, name, k5login_exists)
|
|
+ && k5login_exists) {
|
|
retval = 1;
|
|
logit("Authorized to %s, krb5 principal %s (krb5_kuserok)",
|
|
name, (char *)client->displayname.value);
|
|
@@ -190,9 +289,8 @@ ssh_gssapi_krb5_cmdok(krb5_principal pri
|
|
snprintf(file, sizeof(file), "%s/.k5users", pw->pw_dir);
|
|
/* If both .k5login and .k5users DNE, self-login is ok. */
|
|
if (!k5login_exists && (access(file, F_OK) == -1)) {
|
|
- return (krb5_aname_to_localname(krb_context, principal,
|
|
- sizeof(kuser), kuser) == 0) &&
|
|
- (strcmp(kuser, luser) == 0);
|
|
+ return ssh_krb5_kuserok(krb_context, principal, luser,
|
|
+ k5login_exists);
|
|
}
|
|
if ((fp = fopen(file, "r")) == NULL) {
|
|
int saved_errno = errno;
|
|
diff -up openssh-7.4p1/servconf.c.kuserok openssh-7.4p1/servconf.c
|
|
--- openssh-7.4p1/servconf.c.kuserok 2016-12-23 14:36:07.630465944 +0100
|
|
+++ openssh-7.4p1/servconf.c 2016-12-23 15:11:52.278133344 +0100
|
|
@@ -116,6 +116,7 @@ initialize_server_options(ServerOptions
|
|
options->gss_strict_acceptor = -1;
|
|
options->gss_store_rekey = -1;
|
|
options->gss_kex_algorithms = NULL;
|
|
+ options->use_kuserok = -1;
|
|
options->password_authentication = -1;
|
|
options->kbd_interactive_authentication = -1;
|
|
options->challenge_response_authentication = -1;
|
|
@@ -278,6 +279,8 @@ fill_default_server_options(ServerOption
|
|
if (options->gss_kex_algorithms == NULL)
|
|
options->gss_kex_algorithms = strdup(GSS_KEX_DEFAULT_KEX);
|
|
#endif
|
|
+ if (options->use_kuserok == -1)
|
|
+ options->use_kuserok = 1;
|
|
if (options->password_authentication == -1)
|
|
options->password_authentication = 1;
|
|
if (options->kbd_interactive_authentication == -1)
|
|
@@ -399,7 +402,7 @@ typedef enum {
|
|
sPermitRootLogin, sLogFacility, sLogLevel, sLogVerbose,
|
|
sRhostsRSAAuthentication, sRSAAuthentication,
|
|
sKerberosAuthentication, sKerberosOrLocalPasswd, sKerberosTicketCleanup,
|
|
- sKerberosGetAFSToken, sKerberosUniqueCCache,
|
|
+ sKerberosGetAFSToken, sKerberosUniqueCCache, sKerberosUseKuserok,
|
|
sChallengeResponseAuthentication,
|
|
sPasswordAuthentication, sKbdInteractiveAuthentication,
|
|
sListenAddress, sAddressFamily,
|
|
@@ -478,12 +481,14 @@ static struct {
|
|
{ "kerberosgetafstoken", sUnsupported, SSHCFG_GLOBAL },
|
|
#endif
|
|
{ "kerberosuniqueccache", sKerberosUniqueCCache, SSHCFG_GLOBAL },
|
|
+ { "kerberosusekuserok", sKerberosUseKuserok, SSHCFG_ALL },
|
|
#else
|
|
{ "kerberosauthentication", sUnsupported, SSHCFG_ALL },
|
|
{ "kerberosorlocalpasswd", sUnsupported, SSHCFG_GLOBAL },
|
|
{ "kerberosticketcleanup", sUnsupported, SSHCFG_GLOBAL },
|
|
{ "kerberosgetafstoken", sUnsupported, SSHCFG_GLOBAL },
|
|
{ "kerberosuniqueccache", sUnsupported, SSHCFG_GLOBAL },
|
|
+ { "kerberosusekuserok", sUnsupported, SSHCFG_ALL },
|
|
#endif
|
|
{ "kerberostgtpassing", sUnsupported, SSHCFG_GLOBAL },
|
|
{ "afstokenpassing", sUnsupported, SSHCFG_GLOBAL },
|
|
@@ -1644,6 +1649,10 @@ process_server_config_line(ServerOptions
|
|
*inc_flags &= ~SSHCFG_MATCH_ONLY;
|
|
break;
|
|
|
|
+ case sKerberosUseKuserok:
|
|
+ intptr = &options->use_kuserok;
|
|
+ goto parse_flag;
|
|
+
|
|
case sPermitListen:
|
|
case sPermitOpen:
|
|
if (opcode == sPermitListen) {
|
|
@@ -2016,6 +2025,7 @@ copy_set_server_options(ServerOptions *d
|
|
M_CP_INTOPT(client_alive_interval);
|
|
M_CP_INTOPT(ip_qos_interactive);
|
|
M_CP_INTOPT(ip_qos_bulk);
|
|
+ M_CP_INTOPT(use_kuserok);
|
|
M_CP_INTOPT(rekey_limit);
|
|
M_CP_INTOPT(rekey_interval);
|
|
M_CP_INTOPT(log_level);
|
|
@@ -2309,6 +2319,7 @@ dump_config(ServerOptions *o)
|
|
dump_cfg_fmtint(sKerberosGetAFSToken, o->kerberos_get_afs_token);
|
|
# endif
|
|
dump_cfg_fmtint(sKerberosUniqueCCache, o->kerberos_unique_ccache);
|
|
+ dump_cfg_fmtint(sKerberosUseKuserok, o->use_kuserok);
|
|
#endif
|
|
#ifdef GSSAPI
|
|
dump_cfg_fmtint(sGssAuthentication, o->gss_authentication);
|
|
diff -up openssh-7.4p1/servconf.h.kuserok openssh-7.4p1/servconf.h
|
|
--- openssh-7.4p1/servconf.h.kuserok 2016-12-23 14:36:07.630465944 +0100
|
|
+++ openssh-7.4p1/servconf.h 2016-12-23 14:36:07.645465936 +0100
|
|
@@ -118,6 +118,7 @@ typedef struct {
|
|
* authenticated with Kerberos. */
|
|
int kerberos_unique_ccache; /* If true, the acquired ticket will
|
|
* be stored in per-session ccache */
|
|
+ int use_kuserok;
|
|
int gss_authentication; /* If true, permit GSSAPI authentication */
|
|
int gss_keyex; /* If true, permit GSSAPI key exchange */
|
|
int gss_cleanup_creds; /* If true, destroy cred cache on logout */
|
|
diff -up openssh-7.4p1/sshd_config.5.kuserok openssh-7.4p1/sshd_config.5
|
|
--- openssh-7.4p1/sshd_config.5.kuserok 2016-12-23 14:36:07.637465940 +0100
|
|
+++ openssh-7.4p1/sshd_config.5 2016-12-23 15:14:03.117162222 +0100
|
|
@@ -850,6 +850,10 @@ Specifies whether to automatically destr
|
|
.Cm no
|
|
can lead to overwriting previous tickets by subseqent connections to the same
|
|
user account.
|
|
+.It Cm KerberosUseKuserok
|
|
+Specifies whether to look at .k5login file for user's aliases.
|
|
+The default is
|
|
+.Cm yes .
|
|
.It Cm KexAlgorithms
|
|
Specifies the available KEX (Key Exchange) algorithms.
|
|
Multiple algorithms must be comma-separated.
|
|
@@ -1078,6 +1082,7 @@ Available keywords are
|
|
.Cm IPQoS ,
|
|
.Cm KbdInteractiveAuthentication ,
|
|
.Cm KerberosAuthentication ,
|
|
+.Cm KerberosUseKuserok ,
|
|
.Cm LogLevel ,
|
|
.Cm MaxAuthTries ,
|
|
.Cm MaxSessions ,
|
|
diff -up openssh-7.4p1/sshd_config.kuserok openssh-7.4p1/sshd_config
|
|
--- openssh-7.4p1/sshd_config.kuserok 2016-12-23 14:36:07.631465943 +0100
|
|
+++ openssh-7.4p1/sshd_config 2016-12-23 14:36:07.646465935 +0100
|
|
@@ -73,6 +73,7 @@ ChallengeResponseAuthentication no
|
|
#KerberosOrLocalPasswd yes
|
|
#KerberosTicketCleanup yes
|
|
#KerberosGetAFSToken no
|
|
+#KerberosUseKuserok yes
|
|
|
|
# GSSAPI options
|
|
#GSSAPIAuthentication no
|