bison uses invalid memory in rare situations

[Kees Cook]

Binary package hint: bison

As detailed here:

http://undeadly.org/cgi?action=article&sid=20080708155228

Bison should get fixed too.

http://www.openbsd.org/cgi-bin/cvsweb/src/usr.bin/yacc/skeleton.c.diff?r1=1.28&r2=1.29

Bison does carry an interesting note:

  /* yyn is the number of a rule to reduce with. */
  yylen = yyr2[yyn];

  /* If YYLEN is nonzero, implement the default value of the action:
     `$$ = $1'.

     Otherwise, the following line sets YYVAL to garbage.
     This behavior is undocumented and Bison
     users should not rely upon it. Assigning to YYVAL
     unconditionally makes the parser a bit smaller, and it avoids a
     GCC warning that YYVAL may be used uninitialized. */
  yyval = yyvsp[1-yylen];