How to detect symbol interposition?

[Florian Weimer]

On 06/28/2016 07:56 PM, Mike Frysinger wrote:
> On 28 Jun 2016 16:12, Florian Weimer wrote:
>> I need a way to detect symbol interposition from within libc.
>
> why ?

I want to add a hardened variant of getline which uses 
malloc_usable_size to check chunk size and specified size for consistency.

Not all interposed mallocs interpose malloc_usable_size as well, so I 
need to check for

   (malloc == __libc_malloc)
     == (malloc_usable_size == _libc_malloc_usable_size)

and only do this if equality holds.

Another application is initialization for glibc malloc.  To reduce the 
number of function pointers, I would like to remove the malloc hooks. 
But this means that we need to remove lazy initialization of malloc.  I 
want to add an explicit call into malloc to perform basically what 
ptmalloc_init does today, but only if glibc malloc has not been interposed.

Thanks,
Florian