[PATCH 09/11] locale: Fix UB on add_locale_uint32_array

[Adhemerval Zanella Netto]

On 02/06/25 10:29, Florian Weimer wrote:
> * Adhemerval Zanella Netto:
> 
>> On 20/05/25 09:49, Florian Weimer wrote:
>>> * Adhemerval Zanella:
>>>
>>>> The ubsan triggers:
>>>>
>>>> UBSAN: Undefined behaviour in programs/locfile.c:644:3 null pointer passed as argument 2, nonnull attribute declared at unknown:0:0
>>>>
>>>> The obstack_grow is only required if there is extra elements to be
>>>> inserted (n_elems > 0).
>>>> ---
>>>>  locale/programs/locfile.c | 2 ++
>>>>  1 file changed, 2 insertions(+)
>>>>
>>>> diff --git a/locale/programs/locfile.c b/locale/programs/locfile.c
>>>> index b54fcbbceb..7907c949ea 100644
>>>> --- a/locale/programs/locfile.c
>>>> +++ b/locale/programs/locfile.c
>>>> @@ -641,6 +641,8 @@ add_locale_uint32_array (struct locale_file *file,
>>>>  {
>>>>    align_locale_data (file, LOCFILE_ALIGN);
>>>>    record_offset (file);
>>>> +  if (n_elems == 0)
>>>> +    return;
>>>>    obstack_grow (&file->data, data, n_elems * sizeof (uint32_t));
>>>>    maybe_swap_uint32_obstack (&file->data, n_elems);
>>>>  }
>>>
>>> We should fix the declaration of obstack_grow instead, to align with the
>>> new declarations for memcpy et al.
>>
>> To accept lenght equal 0? It might be an option, I am not sure which is the
>> best option.
> 
> Yes, use the nonnull_if_nonzero if available, or nothing otherwise.

These interfaces are implemented as macros, so we will need to make them
proper functions for this.  And since we do export them, I think we will
either need add some hacks to enable it only for c99 or higher, or add 
internal interfaces. Both seems not ideal.

gnulib still uses macro though and does not handle length to 0.