Fix for bug #40552: Race condition around default_directories

                    in load_defaults() 

load_defaults(), my_search_option_files() and 
my_print_default_files()  utilized a global variable 
containing  a pointer to thread local memory. This could lead 
to race conditions when those functions were called with high 
concurrency. 

Fixed by changing the interface of the said functions to avoid 
the necessity for using a global variable.

Since we cannot change load_defaults() prototype for API
compatibility reasons, it was renamed my_load_defaults().
Now load_defaults() is a thread-unsafe wrapper around
a thread-safe version, my_load_defaults().


mysys/default.c:
  1. Added a thread-safe version of load_defaults(), changed
  load_defaults() with the old interface to be a thread-unsafe
  wrapper around the thread-safe version.
  2. Always use a private MEM_ROOT in my_print_default_files, 
  don't use a global variable.
sql-common/client.c:
  Use a thread-safe version of load_defaults().

1 files changed, 51 insertions, 14 deletions

diff --git a/mysys/default.c b/mysys/default.c
index 6b2b31d43ec..cdd9462c1d1 100644
--- a/mysys/default.c
+++ b/mysys/default.c
@@ -151,7 +151,7 @@ static char *remove_end_comment(char *ptr);
 
 int my_search_option_files(const char *conf_file, int *argc, char ***argv,
                            uint *args_used, Process_option_func func,
-                           void *func_ctx)
+                           void *func_ctx, const char **default_directories)
 {
   const char **dirs, *forced_default_file, *forced_extra_defaults;
   int error= 0;
@@ -359,18 +359,46 @@ int get_defaults_options(int argc, char **argv,
   return org_argc - argc;
 }
 
+/*
+  Wrapper around my_load_defaults() for interface compatibility.
+
+  SYNOPSIS
+    load_defaults()
+    conf_file			Basename for configuration file to search for.
+    				If this is a path, then only this file is read.
+    groups			Which [group] entrys to read.
+				Points to an null terminated array of pointers
+    argc			Pointer to argc of original program
+    argv			Pointer to argv of original program
+
+  NOTES
+
+    This function is NOT thread-safe as it uses a global pointer internally.
+    See also notes for my_load_defaults().
+
+  RETURN
+    0 ok
+    1 The given conf_file didn't exists
+*/
+int load_defaults(const char *conf_file, const char **groups,
+                  int *argc, char ***argv)
+{
+  return my_load_defaults(conf_file, groups, argc, argv, &default_directories);
+}
 
 /*
   Read options from configurations files
 
   SYNOPSIS
-    load_defaults()
+    my_load_defaults()
     conf_file			Basename for configuration file to search for.
     				If this is a path, then only this file is read.
     groups			Which [group] entrys to read.
 				Points to an null terminated array of pointers
     argc			Pointer to argc of original program
     argv			Pointer to argv of original program
+    default_directories         Pointer to a location where a pointer to the list
+                                of default directories will be stored
 
   IMPLEMENTATION
 
@@ -386,13 +414,18 @@ int get_defaults_options(int argc, char **argv,
     that was put in *argv
 
    RETURN
-     0	ok
-     1	The given conf_file didn't exists
+     - If successful, 0 is returned. If 'default_directories' is not NULL,
+     a pointer to the array of default directory paths is stored to a location
+     it points to. That stored value must be passed to my_search_option_files()
+     later.
+     
+     - 1 is returned if the given conf_file didn't exist. In this case, the
+     value pointed to by default_directories is undefined.
 */
 
 
-int load_defaults(const char *conf_file, const char **groups,
-                  int *argc, char ***argv)
+int my_load_defaults(const char *conf_file, const char **groups,
+                  int *argc, char ***argv, const char ***default_directories)
 {
   DYNAMIC_ARRAY args;
   TYPELIB group;
@@ -402,10 +435,11 @@ int load_defaults(const char *conf_file, const char **groups,
   MEM_ROOT alloc;
   char *ptr,**res;
   struct handle_option_ctx ctx;
+  const char **dirs;
   DBUG_ENTER("load_defaults");
 
   init_alloc_root(&alloc,512,0);
-  if ((default_directories= init_default_directories(&alloc)) == NULL)
+  if ((dirs= init_default_directories(&alloc)) == NULL)
     goto err;
   /*
     Check if the user doesn't want any default option processing
@@ -426,6 +460,8 @@ int load_defaults(const char *conf_file, const char **groups,
     (*argc)--;
     *argv=res;
     *(MEM_ROOT*) ptr= alloc;			/* Save alloc root for free */
+    if (default_directories)
+      *default_directories= dirs;
     DBUG_RETURN(0);
   }
 
@@ -444,7 +480,8 @@ int load_defaults(const char *conf_file, const char **groups,
   ctx.group= &group;
 
   error= my_search_option_files(conf_file, argc, argv, &args_used,
-                                handle_default_option, (void *) &ctx);
+                                handle_default_option, (void *) &ctx,
+                                dirs);
   /*
     Here error contains <> 0 only if we have a fully specified conf_file
     or a forced default file
@@ -490,6 +527,10 @@ int load_defaults(const char *conf_file, const char **groups,
     puts("");
     exit(0);
   }
+
+  if (error == 0 && default_directories)
+    *default_directories= dirs;
+
   DBUG_RETURN(error);
 
  err:
@@ -895,15 +936,11 @@ void my_print_default_files(const char *conf_file)
     fputs(conf_file,stdout);
   else
   {
-    /*
-      If default_directories is already initialized, use it.  Otherwise,
-      use a private MEM_ROOT.
-    */
-    const char **dirs = default_directories;
+    const char **dirs;
     MEM_ROOT alloc;
     init_alloc_root(&alloc,512,0);
 
-    if (!dirs && (dirs= init_default_directories(&alloc)) == NULL)
+    if ((dirs= init_default_directories(&alloc)) == NULL)
     {
       fputs("Internal error initializing default directories list", stdout);
     }