libiberty - Segmentation fault when attempting to delete a non-existent element in a hash table

[rocco@tecsiel.it]

Hello people,
the attached C-program can be used to reproduce a segmentation fault
found in libliberty/hashtab.c

I am using a libiberty tar-gzipped source version found in a recent Debian
Archive File (libiberty_20160215.tar.xz) where the first entry in ChangeLog is:
 * 2016-01-27  Iain Buclaw  <ibuclaw@gdcproject.org>

This is the output of the execution of my program before patching the
library:

rocco@nuc.carbo.net 1221> ./bug-remove
Hello world!

  This program creates a hash table with htab_create().
    Then:
      * inserts 2 objects with htab_find_slot(INSERT).
      * delete 1 existent with htab_remove_elt().
      * attempt to delete 1 non existent with htab_remove_elt().
        Boom !!!

Inserting [Hello - 1] ... Ok
Inserting [World! - 2] ... Ok
Searching for [Hello] ... Ok
Searching for [World!] ... Ok
Deleting [Hello] ... Ok
Segmentation fault


And this was the patch I applied in libiberty/libiberty:
rocco@nuc.carbo.net 1222> diff hashtab.c hashtab.c.ORG 
729c729
<   if (!slot || *slot == HTAB_EMPTY_ENTRY)
---
>   if (*slot == HTAB_EMPTY_ENTRY)


Maybe the same error could be also in other different points for
different API functions but I did not check.


/rocco

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