[RFC][BZ #16549] Add sanity check for condvar alignment.

[Florian Weimer]

On 02/11/2014 11:44 PM, Joseph S. Myers wrote:
> On Tue, 11 Feb 2014, Florian Weimer wrote:
>
>> I think the real issue here is our lack of error checking for the futex system
>> call.  strace on the test case shows this:
>
> I'm not sure what we would do with an error here.  Cf
> <https://sourceware.org/glibc/wiki/Style_and_Conventions#Invalid_pointers>
> noting that a crash or assertion failure on an invalid NULL pointer is
> better than returning an error value that would likely be ignored by the
> buggy caller (although it's not obvious to me that diagnosing a misaligned
> pointer through an assertion is worthwhile anyway).

We'd probably have to abort anyway in contexts where an unexpected error 
occurs.  But I find it rather questionable that we completely discard 
the system call results in most cases.

Here, the glibc behavior happens to be correct—silently not locking is 
allowed if the pointer is invalid.  But I don't think we know for sure 
that all unexpected futex errors are due to precondition violations by 
user code.

-- 
Florian Weimer / Red Hat Product Security Team