[PATCH] Declare set*id with warn_unused_result

[Florian Weimer]

On 07/24/2012 03:31 PM, Paul Eggert wrote:
> On 07/24/2012 06:07 AM, Florian Weimer wrote:
>> The set*uid kernel changes have not been backported widely,
>> and software has to run correctly on such kernels
>
> But typically there is no reasonable way to run correctly on
> such kernels, right?  For example, a library function might invoke
> seteuid to temporarily change the EUID, and invoke seteuid again to
> change it back.  If the latter call fails, there's nothing
> the function can do.

It could (and probably should) call abort because something has gone 
horribly wrong.

> If this proposed change were installed, it's
> plausible that an application developer wouldn't notice this
> sort of issue, and would introduce further security bugs
> in an attempt to pacify GCC.

Which issue?  Currently, the application keeps running with an 
unexpected UID, and this has led to privilege escalation 
vulnerabilities.  I don't see how encouraging the programmer to add 
checks could make things any worse.

> Users with unfixed kernels will have the problem regardless
> of the proposed change, since they'll almost invariably be
> using unfixed apps as well.

We fix applications which do not check the results of set*id calls when 
we come across them.  The patch intends to help with this.

I forgot to mention that even current kernels code can return ENOMEM, it 
is just harder to hit.

-- 
Florian Weimer / Red Hat Product Security Team