[PATCH] pwdgrp::read_group(): Don't call free() twice with the same address

[David Rothenberger]

Hi,

This patch avoids the heap corruption that was causing the problem
described in
<http://www.cygwin.com/ml/cygwin/2003-08/msg00364.html>.

In pwdgrp::read_group(), there is loop to free allocated gr_mem
buffers.  That loop checks to see if gr_mem != &null_ptr, but does
not set gr_mem to &null_ptr after free() is called.  Subsequent
calls then attempt to free the same address again, corrupting the
malloc structures.

The tar test case triggers this behavior if there is no /etc
directory available, for some reason.

Dave

======================================================================
ChangeLog:
2003-08-08  David Rothenberger  <[EMAIL PROTECTED]>

        * grp.cc (read_group): Set __group32.gr_mem pointer back to
        &null_ptr after free() is called.


Index: cygwin/grp.cc
===================================================================
RCS file: /cvs/src/src/winsup/cygwin/grp.cc,v
retrieving revision 1.81
diff -u -u -p -r1.81 grp.cc
--- cygwin/grp.cc       30 Jun 2003 13:07:36 -0000      1.81
+++ cygwin/grp.cc       8 Aug 2003 18:29:44 -0000
@@ -75,7 +75,10 @@ pwdgrp::read_group ()
 {
   for (int i = 0; i < gr.curr_lines; i++)
     if ((*group_buf)[i].gr_mem != &null_ptr)
-      free ((*group_buf)[i].gr_mem);
+      {
+        free ((*group_buf)[i].gr_mem);
+        (*group_buf)[i].gr_mem = &null_ptr;
+      }
 
   load ("/etc/group");