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From: Florian Weimer <fweimer@redhat.com>
To: Carlos O'Donell <carlos@redhat.com>
Cc: libc-alpha@sourceware.org
Subject: Re: [PATCH] elf: Assert range of ns argument in _dl_debug_initialize
References: <87y2b04us6.fsf@oldenburg.str.redhat.com>
 <1517d682-9f16-6daf-b2b3-ab716a222a0b@redhat.com>
Date: Mon, 28 Jun 2021 00:51:32 +0200
In-Reply-To: <1517d682-9f16-6daf-b2b3-ab716a222a0b@redhat.com> (Carlos
 O'Donell's message of "Sun, 27 Jun 2021 18:15:52 -0400")
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* 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.

Thanks,
Florian