Re: Fwd: [PATCH v5 00/22] Some rtld-audit fixes

[Florian Weimer via Libc-alpha <libc-alpha@sourceware.org>]

* Adhemerval Zanella:

>> "" for the main executable is widely known.  Usually code uses it to
>> implement a fallback on argv[0] or /proc/self/exe, though.
>
> There are still the issue where audit interface does not have direct
> access to argv[0] from the audited process and '/proc' might also not
> be accessible.  I am still not convinced that provided argv[0] for
> l_name for main executable is worse than "", specially because the
> fallback might not work.

I think it's better to give the auditor a chance to figure out whether
they want to use program_invocation_name (if that's not available in the
inner libc, that's for sure a bug we must fix), AT_EXECFN, or
/proc/self/exe.  If we pick one of these for the auditor, we make it
more difficult to make the appropriate choice.

>> Changing l_addr will break the libgcc unwinder.  It uses l_addr to
>> relocate the program header (see the code I quoted previously).  Not
>> everyone uses the platform unwinder, and the libgcc unwinder is
>> sometimes linked statically.  This is different from the l_name change:
>> The l_addr would definitely cause widespread breakage.
>> 
>>>  - Every use case I can think of for obtaining a link_map from the dl*
>>> functions (dlinfo and dladdr1) will either already have the special 
>>> handling, or won't operate on the main executable, or likely won't opt
>>> to use l_addr (vs. dlsym or dli_fbase) or l_name (vs. dli_fname).
>> 
>> Some special-case the main executable based on l_name, I expect, which
>> is why I'm so reluctant to change l_name.  The GDB comment is actually
>> hinting strongly towards a "" convention (that Solaris broke).
>
> So I take that Solaris does provide the application name to l_name? And
> what kind of breakage it has done on gdb?

Solaris seems to use the pathname argument to execve as l_name,
via AT_SUN_EXECNAME.  I do not know if it is an absolute name.
The documentation for getexecname suggests it may not be:

| Normally this is an absolute pathname, as the majority of commands are
| executed by the shells that append the command name to the user's PATH
| components. If this is not an absolute path, the output of getcwd(3C)
| can be prepended to it to create an absolute path, unless the process
| or one of its ancestors has changed its root directory or current
| working directory since the last successful call to one of the exec
| family of functions.

<https://docs.oracle.com/cd/E36784_01/html/E36874/getexecname-3c.html>

If that's accurate, it would be just like our AT_EXECFN.  I suspect this
won't work for fexecve, so they are just going to fall back to argv[0]
in that case.

Still I think we have 20+ years of doing things our way (the BSD way),
and I do worry about the backwards compatibility impact of such a
change.

Thanks,
Florian