[SSSD] [PATCH] Print pointer contents not address

Stephen Gallagher sgallagh at redhat.com
Tue Jul 10 13:26:12 UTC 2012


On Tue, 2012-07-10 at 15:10 +0200, Jakub Hrozek wrote:
> On Mon, Jul 09, 2012 at 07:28:12AM -0400, Stephen Gallagher wrote:
> > On Sun, 2012-07-08 at 22:02 +0200, Jakub Hrozek wrote:
> > > I was not able to log in today, I was getting krb5_child segfaults. The
> > > attached patch fixed that.
> > 
> > Nack.
> > 
> > I fail to see how this could possibly have caused a segfault. The
> > previous version would have been printing either "true" or "false" based
> > on whether the pointer was NULL or contained a value. This was
> > incorrect, but should be impossible to segfault on.
> 
> Yeah, the segfault was caused by incorrect format string. I'll send a
> separate patch for that issue.
> 
> I assumed this was the reason because I no longer saw the segfault on my
> laptop, but it turned out that the crash went away only because I tested
> a build compiled with -O0, krb5_child was still crashing when compiled
> with -O2.
> 

I hate it when bugs only occur at certain optimization levels...

> > 
> > However, the new patch changes this to a dereference without checking
> > the validity of the offline pointer first. So now you've introduced the
> > possibility of a segfault if the pointer is uninitialized (though it
> > never should be).
> 
> We write into the address earlier anyway, so we depended on the pointer
> validity. I've added a check, 

Ack.
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