s3-parm: clean up defaults when removing global parameters

BUG: https://bugzilla.samba.org/show_bug.cgi?id=11693

When globals are re-initialized, they are cleared and globals' talloc
context is freed. However, parm_table still contains a reference to the
global value in the defaults. This confuses lpcfg_string_free() after
commit 795c543d858b2452f062a02846c2f908fe4cffe4 because it tries to
free already freed pointer which is passed by lp_save_defaults():

....
    case P_STRING:
    case P_USTRING:
                  lpcfg_string_set(Globals.ctx,
                                   &parm_table[i].def.svalue,
                                   *(char **)lp_parm_ptr(NULL, &parm_table[i]));
....

here &parm_table[i].def.svalue is passed to lpcfg_string_free() but it
is a pointer to a value allocated with previous Globals.ctx which
already was freed.

This specifically affects registry backend of smb.conf in lp_load_ex()
where init_globals() called explicitly to re-init globals after
lp_save_defaults() if we have registry backend defined.

Reviewed-by: Uri Simchoni <uri@samba.org>
Signed-off-by: Alexander Bokovoy <ab@samba.org>

Autobuild-User(master): Uri Simchoni <uri@samba.org>
Autobuild-Date(master): Mon Jan 25 23:58:42 CET 2016 on sn-devel-144

1 files changed, 17 insertions, 0 deletions

diff --git a/source3/param/loadparm.c b/source3/param/loadparm.c
index 9f4a2b40640..f8ecab716b4 100644
--- a/source3/param/loadparm.c
+++ b/source3/param/loadparm.c
@@ -399,8 +399,25 @@ static void free_parameters_by_snum(int snum)
  */
 static void free_global_parameters(void)
 {
+	uint32_t i;
+	struct parm_struct *parm;
+
 	free_param_opts(&Globals.param_opt);
 	free_parameters_by_snum(GLOBAL_SECTION_SNUM);
+
+	/* Reset references in the defaults because the context is going to be freed */
+	for (i=0; parm_table[i].label; i++) {
+		parm = &parm_table[i];
+		if ((parm->type == P_STRING) ||
+		    (parm->type == P_USTRING)) {
+			if ((parm->def.svalue != NULL) &&
+			    (*(parm->def.svalue) != '\0')) {
+				if (talloc_parent(parm->def.svalue) == Globals.ctx) {
+					parm->def.svalue = NULL;
+				}
+			}
+		}
+	}
 	TALLOC_FREE(Globals.ctx);
 }