From https://ftp.gnu.org/gnu/bash/bash-4.4-patches/bash44-009

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

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

Bash-Release:	4.4
Patch-ID:	bash44-009

Bug-Reported-by:	Hong Cho <hong.cho@citrix.com>
Bug-Reference-ID:	<c30b5fe62b2543af8297e47ca487c29c@SJCPEX02CL02.citrite.net>
Bug-Reference-URL:	http://lists.gnu.org/archive/html/bug-bash/2016-12/msg00043.html

Bug-Description:

There is a race condition in add_history() that can be triggered by a fatal
signal arriving between the time the history length is updated and the time
the history list update is completed. A later attempt to reference an
invalid history entry can cause a crash.

Patch (apply with `patch -p0'):

*** bash-4.4-patched/lib/readline/history.c	2016-11-11 13:42:49.000000000 -0500
--- b/lib/readline/history.c	2016-12-05 10:37:51.000000000 -0500
***************
*** 280,283 ****
--- b/280,284 ----
  {
    HIST_ENTRY *temp;
+   int new_length;
  
    if (history_stifled && (history_length == history_max_entries))
***************
*** 296,306 ****
        /* Copy the rest of the entries, moving down one slot.  Copy includes
  	 trailing NULL.  */
- #if 0
-       for (i = 0; i < history_length; i++)
- 	the_history[i] = the_history[i + 1];
- #else
        memmove (the_history, the_history + 1, history_length * sizeof (HIST_ENTRY *));
- #endif
  
        history_base++;
      }
--- b/297,303 ----
        /* Copy the rest of the entries, moving down one slot.  Copy includes
  	 trailing NULL.  */
        memmove (the_history, the_history + 1, history_length * sizeof (HIST_ENTRY *));
  
+       new_length = history_length;
        history_base++;
      }
***************
*** 316,320 ****
  	    history_size = DEFAULT_HISTORY_INITIAL_SIZE;
  	  the_history = (HIST_ENTRY **)xmalloc (history_size * sizeof (HIST_ENTRY *));
! 	  history_length = 1;
  	}
        else
--- b/313,317 ----
  	    history_size = DEFAULT_HISTORY_INITIAL_SIZE;
  	  the_history = (HIST_ENTRY **)xmalloc (history_size * sizeof (HIST_ENTRY *));
! 	  new_length = 1;
  	}
        else
***************
*** 326,330 ****
  		xrealloc (the_history, history_size * sizeof (HIST_ENTRY *));
  	    }
! 	  history_length++;
  	}
      }
--- b/323,327 ----
  		xrealloc (the_history, history_size * sizeof (HIST_ENTRY *));
  	    }
! 	  new_length = history_length + 1;
  	}
      }
***************
*** 332,337 ****
    temp = alloc_history_entry ((char *)string, hist_inittime ());
  
!   the_history[history_length] = (HIST_ENTRY *)NULL;
!   the_history[history_length - 1] = temp;
  }
  
--- b/329,335 ----
    temp = alloc_history_entry ((char *)string, hist_inittime ());
  
!   the_history[new_length] = (HIST_ENTRY *)NULL;
!   the_history[new_length - 1] = temp;
!   history_length = new_length;
  }
  
*** 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 8
  
  #endif /* _PATCHLEVEL_H_ */
--- b/26,30 ----
     looks for to find the patch level (for the sccs version string). */
  
! #define PATCHLEVEL 9
  
  #endif /* _PATCHLEVEL_H_ */