Bug #15598 Server crashes in specific case during setting new password

 - When acl_user->host.hostname is NULL compare it as ""


mysql-test/r/grant.result:
  Test user with host ''
mysql-test/t/grant.test:
  Test user with host ''
sql/sql_acl.cc:
  If acl_user->host.hostname is NULL compare it as ""

mysql-test/r/grant.result

@@ -464,3 +464,12 @@ show grants for root@localhost;
 Grants for root@localhost
 GRANT ALL PRIVILEGES ON *.* TO 'root'@'localhost' WITH GRANT OPTION
 set names latin1;
+insert into mysql.user (host, user) values ('', 'mysqltest_7');
+flush privileges;
+set password for mysqltest_7@ = password('systpass');
+show grants for mysqltest_7@;
+Grants for mysqltest_7@
+GRANT USAGE ON *.* TO 'mysqltest_7'@'' IDENTIFIED BY PASSWORD '*2FB071A056F9BB745219D9C876814231DAF46517'
+drop user mysqltest_7@;
+show grants for mysqltest_7@;
+ERROR 42000: There is no such grant defined for user 'mysqltest_7' on host ''

mysql-test/t/grant.test

@@ -421,4 +421,16 @@ revoke all privileges on
 show grants for root@localhost;
 set names latin1;
 
+#
+# Bug #15598 Server crashes in specific case during setting new password
+# - Caused by a user with host ''
+#
+insert into mysql.user (host, user) values ('', 'mysqltest_7');
+flush privileges;
+set password for mysqltest_7@ = password('systpass');
+show grants for mysqltest_7@;
+drop user mysqltest_7@;
+--error 1141
+show grants for mysqltest_7@;
+
 # End of 4.1 tests

sql/sql_acl.cc

@@ -1371,7 +1371,8 @@ find_acl_user(const char *host, const char *user, my_bool exact)
 	acl_user->user && !strcmp(user,acl_user->user))
     {
       if (exact ? !my_strcasecmp(&my_charset_latin1, host,
-                                 acl_user->host.hostname) :
+                                 acl_user->host.hostname ?
+				 acl_user->host.hostname : "") :
           compare_hostname(&acl_user->host,host,host))
       {
 	DBUG_RETURN(acl_user);
@@ -3604,7 +3605,7 @@ ACL_USER *check_acl_user(LEX_USER *user_name,
     if (!(user=acl_user->user))
       user= "";
     if (!(host=acl_user->host.hostname))
-      host= "%";
+      host= "";
     if (!strcmp(user_name->user.str,user) &&
 	!my_strcasecmp(system_charset_info, user_name->host.str, host))
       break;