rpms/openssh
3
0
Fork 0
Code Issues Pull Requests Releases Wiki Activity

fix kuserok patch which checked for the existence of .k5login unconditionally and hence prevented other mechanisms to be used properly

Browse Source
This commit is contained in:
Petr Lautrbach 2014-11-11 11:19:35 +01:00
parent 3c7aefbbeb
commit 4a92081130
3 changed files with 292 additions and 168 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

167
openssh-6.3p1-kuserok.patch
View File

@ -1,167 +0,0 @@
diff -up openssh-6.3p1/auth-krb5.c.kuserok openssh-6.3p1/auth-krb5.c
--- openssh-6.3p1/auth-krb5.c.kuserok 2013-10-11 21:41:42.889087613 +0200
+++ openssh-6.3p1/auth-krb5.c 2013-10-11 21:41:42.905087537 +0200
@@ -55,6 +55,20 @@
extern ServerOptions options;
+int
+ssh_krb5_kuserok(krb5_context krb5_ctx, krb5_principal krb5_user, const char *client)
+{
+ if (options.use_kuserok)
+ 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)
{
@@ -159,7 +173,7 @@ auth_krb5_password(Authctxt *authctxt, c
if (problem)
goto out;
- if (!krb5_kuserok(authctxt->krb5_ctx, authctxt->krb5_user, client)) {
+ if (!ssh_krb5_kuserok(authctxt->krb5_ctx, authctxt->krb5_user, client)) {
problem = -1;
goto out;
}
diff -up openssh-6.3p1/gss-serv-krb5.c.kuserok openssh-6.3p1/gss-serv-krb5.c
--- openssh-6.3p1/gss-serv-krb5.c.kuserok 2013-10-11 21:41:42.901087556 +0200
+++ openssh-6.3p1/gss-serv-krb5.c 2013-10-11 21:46:42.898673597 +0200
@@ -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 *);
/* Initialise the krb5 library, for the stuff that GSSAPI won't do */
@@ -116,7 +117,7 @@ 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) {
retval = 1;
logit("Authorized to %s, krb5 principal %s (krb5_kuserok)",
name, (char *)client->displayname.value);
diff -up openssh-6.3p1/servconf.c.kuserok openssh-6.3p1/servconf.c
--- openssh-6.3p1/servconf.c.kuserok 2013-10-11 21:41:42.896087580 +0200
+++ openssh-6.3p1/servconf.c 2013-10-11 21:48:24.664194016 +0200
@@ -157,6 +157,7 @@ initialize_server_options(ServerOptions
options->ip_qos_interactive = -1;
options->ip_qos_bulk = -1;
options->version_addendum = NULL;
+ options->use_kuserok = -1;
}
void
@@ -310,6 +311,8 @@ fill_default_server_options(ServerOption
options->version_addendum = xstrdup("");
if (options->show_patchlevel == -1)
options->show_patchlevel = 0;
+ if (options->use_kuserok == -1)
+ options->use_kuserok = 1;
/* Turn privilege separation on by default */
if (use_privsep == -1)
@@ -336,7 +339,7 @@ typedef enum {
sPermitRootLogin, sLogFacility, sLogLevel,
sRhostsRSAAuthentication, sRSAAuthentication,
sKerberosAuthentication, sKerberosOrLocalPasswd, sKerberosTicketCleanup,
- sKerberosGetAFSToken,
+ sKerberosGetAFSToken, sKerberosUseKuserok,
sKerberosTgtPassing, sChallengeResponseAuthentication,
sPasswordAuthentication, sKbdInteractiveAuthentication,
sListenAddress, sAddressFamily,
@@ -409,11 +412,13 @@ static struct {
#else
{ "kerberosgetafstoken", sUnsupported, SSHCFG_GLOBAL },
#endif
+ { "kerberosusekuserok", sKerberosUseKuserok, SSHCFG_ALL },
#else
{ "kerberosauthentication", sUnsupported, SSHCFG_ALL },
{ "kerberosorlocalpasswd", sUnsupported, SSHCFG_GLOBAL },
{ "kerberosticketcleanup", sUnsupported, SSHCFG_GLOBAL },
{ "kerberosgetafstoken", sUnsupported, SSHCFG_GLOBAL },
+ { "kerberosusekuserok", sUnsupported, SSHCFG_ALL },
#endif
{ "kerberostgtpassing", sUnsupported, SSHCFG_GLOBAL },
{ "afstokenpassing", sUnsupported, SSHCFG_GLOBAL },
@@ -1515,6 +1520,10 @@ process_server_config_line(ServerOptions
*activep = value;
break;
+ case sKerberosUseKuserok:
+ intptr = &options->use_kuserok;
+ goto parse_flag;
+
case sPermitOpen:
arg = strdelim(&cp);
if (!arg || *arg == '\0')
@@ -1815,6 +1824,7 @@ copy_set_server_options(ServerOptions *d
M_CP_INTOPT(max_authtries);
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);
@@ -2055,6 +2065,7 @@ dump_config(ServerOptions *o)
dump_cfg_fmtint(sUseDNS, o->use_dns);
dump_cfg_fmtint(sAllowTcpForwarding, o->allow_tcp_forwarding);
dump_cfg_fmtint(sUsePrivilegeSeparation, use_privsep);
+ dump_cfg_fmtint(sKerberosUseKuserok, o->use_kuserok);
/* string arguments */
dump_cfg_string(sPidFile, o->pid_file);
diff -up openssh-6.3p1/servconf.h.kuserok openssh-6.3p1/servconf.h
--- openssh-6.3p1/servconf.h.kuserok 2013-10-11 21:41:42.896087580 +0200
+++ openssh-6.3p1/servconf.h 2013-10-11 21:41:42.907087528 +0200
@@ -174,6 +174,7 @@ typedef struct {
int num_permitted_opens;
+ int use_kuserok;
char *chroot_directory;
char *revoked_keys_file;
char *trusted_user_ca_keys;
diff -up openssh-6.3p1/sshd_config.5.kuserok openssh-6.3p1/sshd_config.5
--- openssh-6.3p1/sshd_config.5.kuserok 2013-10-11 21:41:42.898087571 +0200
+++ openssh-6.3p1/sshd_config.5 2013-10-11 21:41:42.907087528 +0200
@@ -675,6 +675,10 @@ Specifies whether to automatically destr
file on logout.
The default is
.Dq yes .
+.It Cm KerberosUseKuserok
+Specifies whether to look at .k5login file for user's aliases.
+The default is
+.Dq yes .
.It Cm KexAlgorithms
Specifies the available KEX (Key Exchange) algorithms.
Multiple algorithms must be comma-separated.
@@ -833,6 +837,7 @@ Available keywords are
.Cm HostbasedUsesNameFromPacketOnly ,
.Cm KbdInteractiveAuthentication ,
.Cm KerberosAuthentication ,
+.Cm KerberosUseKuserok ,
.Cm MaxAuthTries ,
.Cm MaxSessions ,
.Cm PasswordAuthentication ,
diff -up openssh-6.3p1/sshd_config.kuserok openssh-6.3p1/sshd_config
--- openssh-6.3p1/sshd_config.kuserok 2013-10-11 21:41:42.898087571 +0200
+++ openssh-6.3p1/sshd_config 2013-10-11 21:41:42.907087528 +0200
@@ -86,6 +86,7 @@ ChallengeResponseAuthentication no
#KerberosOrLocalPasswd yes
#KerberosTicketCleanup yes
#KerberosGetAFSToken no
+#KerberosUseKuserok yes
# GSSAPI options
#GSSAPIAuthentication no

291
openssh-6.4p1-kuserok.patch Normal file
View File

@ -0,0 +1,291 @@
diff --git a/auth-krb5.c b/auth-krb5.c
index 7c83f59..966b4cb 100644
--- a/auth-krb5.c
+++ b/auth-krb5.c
@@ -54,6 +54,21 @@
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)
{
@@ -157,7 +172,9 @@ auth_krb5_password(Authctxt *authctxt, const char *password)
if (problem)
goto out;
- if (!krb5_kuserok(authctxt->krb5_ctx, authctxt->krb5_user, client)) {
+ /* 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, client, !options.use_kuserok)) {
problem = -1;
goto out;
}
diff --git a/gss-serv-krb5.c b/gss-serv-krb5.c
index b4d479e..a9326a7 100644
--- a/gss-serv-krb5.c
+++ b/gss-serv-krb5.c
@@ -67,6 +67,7 @@ static int ssh_gssapi_krb5_cmdok(krb5_principal, const char *, const char *,
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 *client, char *name)
/* 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);
@@ -171,9 +270,8 @@ ssh_gssapi_krb5_cmdok(krb5_principal principal, const char *name,
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 --git a/servconf.c b/servconf.c
index 277b2bd..1e88905 100644
--- a/servconf.c
+++ b/servconf.c
@@ -157,6 +157,7 @@ initialize_server_options(ServerOptions *options)
options->ip_qos_interactive = -1;
options->ip_qos_bulk = -1;
options->version_addendum = NULL;
+ options->use_kuserok = -1;
}
void
@@ -310,6 +311,8 @@ fill_default_server_options(ServerOptions *options)
options->version_addendum = xstrdup("");
if (options->show_patchlevel == -1)
options->show_patchlevel = 0;
+ if (options->use_kuserok == -1)
+ options->use_kuserok = 1;
/* Turn privilege separation on by default */
if (use_privsep == -1)
@@ -336,7 +339,7 @@ typedef enum {
sPermitRootLogin, sLogFacility, sLogLevel,
sRhostsRSAAuthentication, sRSAAuthentication,
sKerberosAuthentication, sKerberosOrLocalPasswd, sKerberosTicketCleanup,
- sKerberosGetAFSToken,
+ sKerberosGetAFSToken, sKerberosUseKuserok,
sKerberosTgtPassing, sChallengeResponseAuthentication,
sPasswordAuthentication, sKbdInteractiveAuthentication,
sListenAddress, sAddressFamily,
@@ -409,11 +412,13 @@ static struct {
#else
{ "kerberosgetafstoken", sUnsupported, SSHCFG_GLOBAL },
#endif
+ { "kerberosusekuserok", sKerberosUseKuserok, SSHCFG_ALL },
#else
{ "kerberosauthentication", sUnsupported, SSHCFG_ALL },
{ "kerberosorlocalpasswd", sUnsupported, SSHCFG_GLOBAL },
{ "kerberosticketcleanup", sUnsupported, SSHCFG_GLOBAL },
{ "kerberosgetafstoken", sUnsupported, SSHCFG_GLOBAL },
+ { "kerberosusekuserok", sUnsupported, SSHCFG_ALL },
#endif
{ "kerberostgtpassing", sUnsupported, SSHCFG_GLOBAL },
{ "afstokenpassing", sUnsupported, SSHCFG_GLOBAL },
@@ -1515,6 +1520,10 @@ process_server_config_line(ServerOptions *options, char *line,
*activep = value;
break;
+ case sKerberosUseKuserok:
+ intptr = &options->use_kuserok;
+ goto parse_flag;
+
case sPermitOpen:
arg = strdelim(&cp);
if (!arg || *arg == '\0')
@@ -1815,6 +1824,7 @@ copy_set_server_options(ServerOptions *dst, ServerOptions *src, int preauth)
M_CP_INTOPT(max_authtries);
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);
@@ -2055,6 +2065,7 @@ dump_config(ServerOptions *o)
dump_cfg_fmtint(sUseDNS, o->use_dns);
dump_cfg_fmtint(sAllowTcpForwarding, o->allow_tcp_forwarding);
dump_cfg_fmtint(sUsePrivilegeSeparation, use_privsep);
+ dump_cfg_fmtint(sKerberosUseKuserok, o->use_kuserok);
/* string arguments */
dump_cfg_string(sPidFile, o->pid_file);
diff --git a/servconf.h b/servconf.h
index 57752cb..615aaba 100644
--- a/servconf.h
+++ b/servconf.h
@@ -174,6 +174,7 @@ typedef struct {
int num_permitted_opens;
+ int use_kuserok;
char *chroot_directory;
char *revoked_keys_file;
char *trusted_user_ca_keys;
diff -up openssh-6.3p1/sshd_config.5.kuserok openssh-6.3p1/sshd_config.5
--- openssh-6.3p1/sshd_config.5.kuserok 2013-10-11 21:41:42.898087571 +0200
+++ openssh-6.3p1/sshd_config.5 2013-10-11 21:41:42.907087528 +0200
@@ -675,6 +675,10 @@ Specifies whether to automatically destr
file on logout.
The default is
.Dq yes .
+.It Cm KerberosUseKuserok
+Specifies whether to look at .k5login file for user's aliases.
+The default is
+.Dq yes .
.It Cm KexAlgorithms
Specifies the available KEX (Key Exchange) algorithms.
Multiple algorithms must be comma-separated.
@@ -833,6 +837,7 @@ Available keywords are
.Cm HostbasedUsesNameFromPacketOnly ,
.Cm KbdInteractiveAuthentication ,
.Cm KerberosAuthentication ,
+.Cm KerberosUseKuserok ,
.Cm MaxAuthTries ,
.Cm MaxSessions ,
.Cm PasswordAuthentication ,
diff -up openssh-6.3p1/sshd_config.kuserok openssh-6.3p1/sshd_config
--- openssh-6.3p1/sshd_config.kuserok 2013-10-11 21:41:42.898087571 +0200
+++ openssh-6.3p1/sshd_config 2013-10-11 21:41:42.907087528 +0200
@@ -86,6 +86,7 @@ ChallengeResponseAuthentication no
#KerberosOrLocalPasswd yes
#KerberosTicketCleanup yes
#KerberosGetAFSToken no
+#KerberosUseKuserok yes
# GSSAPI options
#GSSAPIAuthentication no

2
openssh.spec
View File

@ -177,7 +177,7 @@ Patch800: openssh-6.3p1-gsskex.patch
Patch801: openssh-6.3p1-force_krb.patch
Patch900: openssh-6.1p1-gssapi-canohost.patch
#https://bugzilla.mindrot.org/show_bug.cgi?id=1780
Patch901: openssh-6.3p1-kuserok.patch
Patch901: openssh-6.4p1-kuserok.patch
# use default_ccache_name from /etc/krb5.conf (#991186)
Patch902: openssh-6.3p1-krb5-use-default_ccache_name.patch
# increase the size of the Diffie-Hellman groups (#1010607)