Merge tnurnberg@bk-internal.mysql.com:/home/bk/mysql-4.1-opt

into  sin.intern.azundris.com:/misc/mysql/31588/41-31588

mysql-test/r/variables.result

@@ -561,3 +561,6 @@ set @@query_prealloc_size = @test;
 select @@query_prealloc_size = @test;
 @@query_prealloc_size = @test
 1
+set global sql_mode=repeat('a',80);
+ERROR 42000: Variable 'sql_mode' can't be set to the value of 'aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa'
+End of 4.1 tests

mysql-test/t/variables.test

@@ -447,4 +447,11 @@ set @test = @@query_prealloc_size;
 set @@query_prealloc_size = @test;
 select @@query_prealloc_size = @test;
 
-# End of 4.1 tests
+#
+# Bug#31588 buffer overrun when setting variables
+#
+# Buffer-size Off By One. Should throw valgrind-warning without fix #31588.
+--error 1231
+set global sql_mode=repeat('a',80);
+
+--echo End of 4.1 tests

sql/set_var.cc

@@ -1573,7 +1573,7 @@ bool sys_var::check_set(THD *thd, set_var *var, TYPELIB *enum_names)
 					    &not_used));
     if (error_len)
     {
-      strmake(buff, error, min(sizeof(buff), error_len));
+      strmake(buff, error, min(sizeof(buff) - 1, error_len));
       goto err;
     }
   }