Re: + signal-always-clear-sa_restorer-on-execve.patch added to -mm tree

[Greg KH <gregkh@linuxfoundation.org>]

On Mon, Mar 11, 2013 at 02:01:30PM -0700, Andrew Morton wrote:
> On Mon, 11 Mar 2013 13:37:53 -0700 Kees Cook <keescook@chromium.org> wrote:
> 
> > ...
> >
> 
> (pop toasting undone)
> 
> > > Subject: signal: always clear sa_restorer on execve
> > >
> > > When the new signal handlers are set up, the location of sa_restorer is
> > > not cleared, leaking a parent process's address space location to
> > > children.  This allows for a potential bypass of the parent's ASLR by
> > > examining the sa_restorer value returned when calling sigaction().
> > >
> > > Based on what should be considered "secret" about addresses, it only
> > > matters across the exec not the fork (since the VMAs haven't changed until
> > > the exec).  But since exec sets SIG_DFL and keeps sa_restorer, this is
> > > where it should be fixed.
> >
> > A note for backporters: you'll likely want to change
> > __ARCH_HAS_SA_RESTORER to SA_RESTORER, since the former was recently
> > introduced. If not, this will apply but not actually do any good.
> 
> I added this to the changelog, but I fear people won't read it!  Is
> there any clever way in which we can have one patch which will work OK
> in both old and new kernels?  I can't think of one...

I'll store it in my stable inbox and will hope to remember it when it
hits Linus's tree...

thanks,

greg k-h