Re: [PATCH 14/20] exit/syscall_user_dispatch: Send ordinary signals on failure

Kees Cook
2021-10-21T16:25:39Z

On Wed, Oct 20, 2021 at 12:44:00PM -0500, Eric W. Biederman wrote:
> Use force_fatal_sig instead of calling do_exit directly. This ensures
> the ordinary signal handling path gets invoked, core dumps as
> appropriate get created, and for multi-threaded processes all of the
> threads are terminated not just a single thread.
>
> When asked Gabriel Krisman Bertazi <krisman@collabora.com> said [1]:
> > ebiederm@xmission.com (Eric W. Biederman) asked:
> >
> > > Why does do_syscal_user_dispatch call do_exit(SIGSEGV) and
> > > do_exit(SIGSYS) instead of force_sig(SIGSEGV) and force_sig(SIGSYS)?
> > >
> > > Looking at the code these cases are not expected to happen, so I would
> > > be surprised if userspace depends on any particular behaviour on the
> > > failure path so I think we can change this.
> >
> > Hi Eric,
> >
> > There is not really a good reason, and the use case that originated the
> > feature doesn't rely on it.
> >
> > Unless I'm missing yet another problem and others correct me, I think
> > it makes sense to change it as you described.
> >
> > > Is using do_exit in this way something you copied from seccomp?
> >
> > I'm not sure, its been a while, but I think it might be just that. The
> > first prototype of SUD was implemented as a seccomp mode.
>
> If at some point it becomes interesting we could relax
> "force_fatal_sig(SIGSEGV)" to instead say
> "force_sig_fault(SIGSEGV, SEGV_MAPERR, sd->selector)".
>
> I avoid doing that in this patch to avoid making it possible
> to catch currently uncatchable signals.
>
> Cc: Gabriel Krisman Bertazi <krisman@collabora.com>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Andy Lutomirski <luto@kernel.org>
> [1] https://lkml.kernel.org/r/87mtr6gdvi.fsf@collabora.com
> Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>

Yeah, looks good. Should be no visible behavior change.

Reviewed-by: Kees Cook <keescook@chromium.org>

--
Kees Cook