Bug #56798 : Wrong credentials assigned when using a proxy user.

Fixed incorrect handling of user credentials when authenticating
via proxy user. Now the server will use the proxies user's 
access mask and host to update the security context runtime 
structure when logging in.

Fixed a compilation warning with the embedded library.

Fixed a crash when doing a second GRANT PROXY on ''@'' due to 
incomplete equality check logic.

mysql-test/r/plugin_auth.result

@@ -210,3 +210,28 @@ SELECT @@LOCAL.external_user;
 DROP USER plug;
 DROP USER plug_dest;
 ## END @@external_user tests
+#
+#  Bug #56798 : Wrong credentials assigned when using a proxy user.
+#
+GRANT ALL PRIVILEGES ON *.* TO power_user;
+GRANT USAGE ON anonymous_db.* TO ''@''
+  IDENTIFIED WITH 'test_plugin_server' AS 'power_user';
+GRANT PROXY ON power_user TO ''@'';
+CREATE DATABASE confidential_db;
+SELECT user(),current_user(),@@proxy_user;
+user()	current_user()	@@proxy_user
+test_login_user@localhost	power_user@%	''@''
+DROP USER power_user;
+DROP USER ''@'';
+DROP DATABASE confidential_db;
+# Test case #2 (crash with double grant proxy)
+CREATE USER ''@'' IDENTIFIED WITH 'test_plugin_server' AS 'standard_user';
+CREATE USER standard_user;
+CREATE DATABASE shared;
+GRANT ALL PRIVILEGES ON shared.* TO standard_user;
+GRANT PROXY ON standard_user TO ''@'';
+#should not crash
+GRANT PROXY ON standard_user TO ''@'';
+DROP USER ''@'';
+DROP USER standard_user;
+DROP DATABASE shared;

mysql-test/t/plugin_auth.test

@@ -296,3 +296,37 @@ disconnect plug_con;
 DROP USER plug;
 DROP USER plug_dest;
 --echo ## END @@external_user tests
+
+--echo #
+--echo #  Bug #56798 : Wrong credentials assigned when using a proxy user.
+--echo #
+
+GRANT ALL PRIVILEGES ON *.* TO power_user;
+GRANT USAGE ON anonymous_db.* TO ''@''
+  IDENTIFIED WITH 'test_plugin_server' AS 'power_user';
+GRANT PROXY ON power_user TO ''@'';
+CREATE DATABASE confidential_db;
+
+connect(plug_con,localhost, test_login_user, power_user, confidential_db);
+SELECT user(),current_user(),@@proxy_user;
+
+connection default;
+disconnect plug_con;
+
+DROP USER power_user;
+DROP USER ''@'';
+DROP DATABASE confidential_db;
+
+--echo # Test case #2 (crash with double grant proxy)
+
+CREATE USER ''@'' IDENTIFIED WITH 'test_plugin_server' AS 'standard_user';
+CREATE USER standard_user;
+CREATE DATABASE shared;
+GRANT ALL PRIVILEGES ON shared.* TO standard_user;
+GRANT PROXY ON standard_user TO ''@'';
+--echo #should not crash
+GRANT PROXY ON standard_user TO ''@'';
+
+DROP USER ''@'';
+DROP USER standard_user;
+DROP DATABASE shared;

sql/sql_acl.cc

@@ -318,6 +318,8 @@ class ACL_PROXY_USER :public ACL_ACCESS
   bool get_with_grant() { return with_grant; }
   const char *get_user() { return user; }
   const char *get_host() { return host.hostname; }
+  const char *get_proxied_user() { return proxied_user; }
+  const char *get_proxied_host() { return proxied_host.hostname; }
   void set_user(MEM_ROOT *mem, const char *user_arg) 
   { 
     user= user_arg && *user_arg ?  strdup_root (mem, user_arg) : NULL; 
@@ -373,6 +375,13 @@ class ACL_PROXY_USER :public ACL_ACCESS
                                                   proxied_user, TRUE))));
   }
 
+
+  inline static bool auth_element_equals(const char *a, const char *b)
+  {
+    return (a == b || (a != NULL && b != NULL && !strcmp(a,b)));
+  }
+
+
   bool pk_equals (ACL_PROXY_USER *grant)
   {
     DBUG_ENTER ("pk_equals");
@@ -389,15 +398,15 @@ class ACL_PROXY_USER :public ACL_ACCESS
                           proxied_host.hostname ? proxied_host.hostname : "<NULL>",
                           grant->proxied_host.hostname ? 
                             grant->proxied_host.hostname : "<NULL>"));
-    DBUG_RETURN(((!user && !grant->user) || !strcmp (user, grant->user)) &&
-                ((!proxied_user && !grant->proxied_user) ||
-                 !strcmp (proxied_user, grant->proxied_user)) &&
-                ((!host.hostname && !grant->host.hostname) || 
-                 !strcmp (host.hostname, grant->host.hostname)) &&
-                ((!proxied_host.hostname && !grant->proxied_host.hostname) || 
-                 !strcmp (proxied_host.hostname, grant->proxied_host.hostname)));
+
+    DBUG_RETURN(auth_element_equals(user, grant->user) &&
+                auth_element_equals(proxied_user, grant->proxied_user) &&
+                auth_element_equals(host.hostname, grant->host.hostname) &&
+                auth_element_equals(proxied_host.hostname, 
+                                    grant->proxied_host.hostname));
   }
 
+
   bool granted_on (const char *host_arg, const char *user_arg)
   {
     return (((!user && (!user_arg || !user_arg[0])) ||
@@ -406,6 +415,7 @@ class ACL_PROXY_USER :public ACL_ACCESS
              (host.hostname && host_arg && !strcmp (host.hostname, host_arg))));
   }
 
+
   void print_grant (String *str)
   {
     str->append(STRING_WITH_LEN("GRANT PROXY ON '"));
@@ -7044,12 +7054,12 @@ template class List<LEX_USER>;
   @param user              the logged in user (proxy user)
   @param authenticated_as  the effective user a plugin is trying to 
                            impersonate as (proxied user)
-  @return                  status
-    @retval FALSE          OK
-    @retval TRUE           user can't impersonate proxied user
+  @return                  proxy user definition
+    @retval NULL           proxy user definition not found or not applicable
+    @retval non-null       the proxy user data
 */
 
-static bool 
+static ACL_PROXY_USER *
 acl_find_proxy_user(const char *user, const char *host, const char *ip, 
                     const char *authenticated_as, bool *proxy_used)
 {
@@ -7061,7 +7071,7 @@ acl_find_proxy_user(const char *user, const char *host, const char *ip,
   if (!strcmp (authenticated_as, user))
   {
     DBUG_PRINT ("info", ("user is the same as authenticated_as"));
-    DBUG_RETURN (FALSE);
+    DBUG_RETURN (NULL);
   }
 
   *proxy_used= TRUE; 
@@ -7070,10 +7080,10 @@ acl_find_proxy_user(const char *user, const char *host, const char *ip,
     ACL_PROXY_USER *proxy= dynamic_element (&acl_proxy_users, i, 
                                             ACL_PROXY_USER *);
     if (proxy->matches (host, user, ip, authenticated_as))
-      DBUG_RETURN(FALSE);
+      DBUG_RETURN(proxy);
   }
 
-  DBUG_RETURN (TRUE);
+  DBUG_RETURN (NULL);
 }
 
 
@@ -8676,6 +8686,7 @@ static void server_mpvio_info(MYSQL_PLUGIN_VIO *vio,
   mpvio_info(mpvio->net->vio, info);
 }
 
+#ifndef NO_EMBEDDED_ACCESS_CHECKS
 static bool acl_check_ssl(THD *thd, const ACL_USER *acl_user)
 {
 #if defined(HAVE_OPENSSL)
@@ -8780,6 +8791,7 @@ static bool acl_check_ssl(THD *thd, const ACL_USER *acl_user)
   }
   return 1;
 }
+#endif
 
 
 static int do_auth_once(THD *thd, const LEX_STRING *auth_plugin_name,
@@ -9006,25 +9018,51 @@ acl_authenticate(THD *thd, uint connect_errors, uint com_change_user_pkt_len)
   {
 #ifndef NO_EMBEDDED_ACCESS_CHECKS
     bool is_proxy_user= FALSE;
-    const char *auth_user = mpvio.acl_user->user ? mpvio.acl_user->user : "";
+    const char *auth_user = acl_user->user ? acl_user->user : "";
+    ACL_PROXY_USER *proxy_user;
     /* check if the user is allowed to proxy as another user */
-    if (acl_find_proxy_user(auth_user, sctx->host, sctx->ip, 
-                            mpvio.auth_info.authenticated_as,
-                            &is_proxy_user))
+    proxy_user= acl_find_proxy_user(auth_user, sctx->host, sctx->ip,
+                                    mpvio.auth_info.authenticated_as,
+                                          &is_proxy_user);
+    if (is_proxy_user)
     {
-      if (!thd->is_error())
-        login_failed_error(&mpvio, mpvio.auth_info.password_used);
-      DBUG_RETURN(1);
-    }
+      ACL_USER *acl_proxy_user;
+
+      /* we need to find the proxy user, but there was none */
+      if (!proxy_user)
+      {
+        if (!thd->is_error())
+          login_failed_error(&mpvio, mpvio.auth_info.password_used);
+        DBUG_RETURN(1);
+      }
 
-    if (is_proxy_user)
       my_snprintf(sctx->proxy_user, sizeof (sctx->proxy_user) - 1,
                   "'%s'@'%s'", auth_user,
                   acl_user->host.hostname ? acl_user->host.hostname : "");
+
+      /* we're proxying : find the proxy user definition */
+      mysql_mutex_lock(&acl_cache->lock);
+      acl_proxy_user= find_acl_user(proxy_user->get_proxied_host() ? 
+                                    proxy_user->get_proxied_host() : "",
+                                    mpvio.auth_info.authenticated_as, TRUE);
+      if (!acl_proxy_user)
+      {
+        if (!thd->is_error())
+          login_failed_error(&mpvio, mpvio.auth_info.password_used);
+        mysql_mutex_unlock(&acl_cache->lock);
+        DBUG_RETURN(1);
+      }
+      acl_user= acl_proxy_user->copy(thd->mem_root);
+      mysql_mutex_unlock(&acl_cache->lock);
+    }
 #endif
 
     sctx->master_access= acl_user->access;
-    strmake(sctx->priv_user, mpvio.auth_info.authenticated_as, USERNAME_LENGTH - 1);
+    if (acl_user->user)
+      strmake(sctx->priv_user, acl_user->user, USERNAME_LENGTH - 1);
+    else
+      *sctx->priv_user= 0;
+
     if (acl_user->host.hostname)
       strmake(sctx->priv_host, acl_user->host.hostname, MAX_HOSTNAME - 1);
     else