[PATCH] libio: Disable vtable validation in case of interposition [BZ #23313]

[Florian Weimer]

On 06/22/2018 12:15 PM, Szabolcs Nagy wrote:
> On 21/06/18 22:20, Florian Weimer wrote:
>>> +/* Some variants of libstdc++ interpose _IO_2_1_stdin_ etc. and
>>> +Â Â  install their own vtables directly, without calling _IO_init or
>>> +   other functions.  Detect this by looking at the vtables values
>>> +   during startup, and disable vtable validation in this case.  */
>>> +__attribute__ ((constructor))
>>> +static void
>>> +check_stdfiles_vtables (void)
>>> +{
>>> +Â  if (_IO_2_1_stdin_.vtable != &_IO_file_jumps
>>> +Â Â Â Â Â  || _IO_2_1_stdout_.vtable != &_IO_file_jumps
>>> +Â Â Â Â Â  || _IO_2_1_stderr_.vtable != &_IO_file_jumps)
>>> +Â Â Â  IO_set_accept_foreign_vtables (&_IO_vtable_check);
>>> +}
>>
>> Any comments on this?
>>
> 
> is this useful to do with static linking too?
> (i'd assume ctor ordering is not well defined then
> so stdio access can happen before this check)
> 
> with dynamic linking the check looks ok to me
> (i did not think about the copy relocation issue)

Right.  I don't think we need to support static linking for backwards 
compatibility with these old libraries, so I'll “#ifndef SHARED” around 
the constructor.

Thanks,
Florian