From https://ftp.gnu.org/gnu/bash/bash-4.4-patches/bash44-004

Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

			     BASH PATCH REPORT
			     =================

Bash-Release:	4.4
Patch-ID:	bash44-004

Bug-Reported-by:	Christian Weisgerber <naddy@mips.inka.de>
Bug-Reference-ID:	<20161101160302.GB54856@lorvorc.mips.inka.de>
Bug-Reference-URL:	http://lists.gnu.org/archive/html/bug-bash/2016-11/msg00004.html

Bug-Description:

There is a race condition that can result in bash referencing freed memory
when freeing data associated with the last process substitution.

Patch (apply with `patch -p0'):

*** a/bash-4.4/jobs.c	2016-08-23 16:38:44.000000000 -0400
--- b/jobs.c	2016-11-02 18:24:45.000000000 -0400
***************
*** 454,457 ****
--- 454,472 ----
  }
  
+ void
+ discard_last_procsub_child ()
+ {
+   PROCESS *disposer;
+   sigset_t set, oset;
+ 
+   BLOCK_CHILD (set, oset);
+   disposer = last_procsub_child;
+   last_procsub_child = (PROCESS *)NULL;
+   UNBLOCK_CHILD (oset);
+ 
+   if (disposer)
+     discard_pipeline (disposer);
+ }
+ 
  struct pipeline_saver *
  alloc_pipeline_saver ()
*** a/bash-4.4/jobs.h	2016-04-27 10:35:51.000000000 -0400
--- b/jobs.h	2016-11-02 18:25:08.000000000 -0400
***************
*** 191,194 ****
--- 191,195 ----
  extern void stop_making_children __P((void));
  extern void cleanup_the_pipeline __P((void));
+ extern void discard_last_procsub_child __P((void));
  extern void save_pipeline __P((int));
  extern PROCESS *restore_pipeline __P((int));
*** a/bash-4.4/subst.c	2016-08-30 16:46:38.000000000 -0400
--- b/subst.c	2016-11-02 18:23:24.000000000 -0400
***************
*** 5809,5816 ****
  #if defined (JOB_CONTROL)
        if (last_procsub_child)
! 	{
! 	  discard_pipeline (last_procsub_child);
! 	  last_procsub_child = (PROCESS *)NULL;
! 	}
        last_procsub_child = restore_pipeline (0);
  #endif
--- 5834,5838 ----
  #if defined (JOB_CONTROL)
        if (last_procsub_child)
! 	discard_last_procsub_child ();
        last_procsub_child = restore_pipeline (0);
  #endif
*** a/bash-4.4/patchlevel.h	2016-06-22 14:51:03.000000000 -0400
--- b/patchlevel.h	2016-10-01 11:01:28.000000000 -0400
***************
*** 26,30 ****
     looks for to find the patch level (for the sccs version string). */
  
! #define PATCHLEVEL 3
  
  #endif /* _PATCHLEVEL_H_ */
--- 26,30 ----
     looks for to find the patch level (for the sccs version string). */
  
! #define PATCHLEVEL 4
  
  #endif /* _PATCHLEVEL_H_ */