Re: clang's Undefined Sanitizer

[Paul Eggert]

On 08/22/2017 10:39 AM, Adhemerval Zanella wrote:
> In fact I decided to *not* sync flexmember because with
> following patch I intend to send (which are in the original thread)
> make flexmember unnecessary.

I see that you sent these proposed patches to glibc glob in the thread 
starting here:

https://sourceware.org/ml/libc-alpha/2017-08/msg01079.html

and I am looking into merging that into Gnulib glob. However, I don't 
see why the patch makes flexmember unnecessary. Even with that patch, 
there is still a datatype 'struct globnames' that has a fixed-size 
member array 'names', and the code still indexes the 'names' component 
past its bounds. That is, the recently-fixed problem is not 
out-of-bounds access into a local variable; it is out-of-bounds access 
into either malloc- or alloca-allocated storage, via a pointer to a type 
that has fixed-size bounds; the C standard does not allow this. So as 
far as I can see, a fix is still necessary even with your patch.

I'll try to resolve this and come up with a patch to Gnulib, and also 
with a patch to follow on to your proposed glibc patch. There are 
several other details that need to be looked at.