Re: [PATCH] elf: Assert range of ns argument in _dl_debug_initialize

[Carlos O'Donell <carlos@redhat.com>]

On 6/27/21 6:51 PM, Florian Weimer wrote:
> * Carlos O'Donell:
> 
>>> diff --git a/elf/dl-debug.c b/elf/dl-debug.c
>>> index 2cd5f09753..85b087455e 100644
>>> --- a/elf/dl-debug.c
>>> +++ b/elf/dl-debug.c
>>> @@ -16,6 +16,8 @@
>>>     License along with the GNU C Library; if not, see
>>>     <https://www.gnu.org/licenses/>.  */
>>>  
>>> +#include <array_length.h>
>>> +#include <assert.h>
>>>  #include <ldsodefs.h>
>>>  
>>>  
>>> @@ -49,7 +51,11 @@ _dl_debug_initialize (ElfW(Addr) ldbase, Lmid_t ns)
>>>    if (ns == LM_ID_BASE)
>>>      r = &_r_debug;
>>>    else
>>> -    r = &GL(dl_ns)[ns]._ns_debug;
>>> +    {
>>> +      assert (ns >= 0);
>>> +      assert (ns < array_length (GL (dl_ns)));
>>
>> The check in _dl_map_object is:
>>   assert (nsid >= 0);
>>   assert (nsid < GL(dl_nns));
>>
>> Should we be consistent one way or the other?
> 
> I wasn't sure if _dl_debug_initialize can be called with a
> not-yet-allocated (or already-deallocated) namespace ID.  _dl_map_object
> is somewhat higher-level, so it's not surprising that it expects an
> active ID.  An out-of-bounds array access is clearly invalid, though.

Assert on the tighter bound and we'll see? :-)

-- 
Cheers,
Carlos.