[PATCH] elf: Refuse to dlopen PIE objects [BZ #24323]

[Florian Weimer]

* Carlos O'Donell:

>>     ifeq (yes,$(build-shared))
>>   # NB: Please keep cet-built-dso in sysdeps/x86/Makefile in sync with
>> diff --git a/elf/dl-load.c b/elf/dl-load.c
>> index 2bbef81b6e..9b0c1406c9 100644
>> --- a/elf/dl-load.c
>> +++ b/elf/dl-load.c
>> @@ -1158,6 +1158,10 @@ _dl_map_object_from_fd (const char *name, const char *origname, int fd,
>>   	goto call_lose;
>>         }
>>   +    /* dlopen of an executable is not valid because it is not
>> possible
>> +       to perform proper relocations and run the ELF constructors.
>> +       For PIE, the check needs the dynamic section, so there is
>> +       another check below.  */
>
> Suggest you mention exactly which relocations are the problem.
> I assume it's COPY relocs into the main executable which can't be
> done twice, because both execs will want to reference their own
> copy. Likewise the problem with ELF constructors should be expanded
> with more details.

I assume that static TLS is also negatively impacted.  TLS variables
from the dlopen'ed PIE binary and the real main program will probably
overlap.

Thanks,
Florian