On Thu, Feb 10, 2022 at 05:18:39PM +0100, Jann Horn wrote:
> On Thu, Feb 10, 2022 at 3:53 AM Kees Cook <keescook@xxxxxxxxxxxx> wrote:
> > Fatal SIGSYS signals were not being delivered to pid namespace init
> > processes. Make sure the SIGNAL_UNKILLABLE doesn't get set for these
> > cases.
> >
> > Reported-by: Robert Święcki <robert@xxxxxxxxxxx>
> > Suggested-by: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx>
> > Fixes: 00b06da29cf9 ("signal: Add SA_IMMUTABLE to ensure forced siganls do not get changed")
> > Cc: stable@xxxxxxxxxxxxxxx
> > Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
> > ---
> > kernel/signal.c | 5 +++--
> > 1 file changed, 3 insertions(+), 2 deletions(-)
> >
> > diff --git a/kernel/signal.c b/kernel/signal.c
> > index 38602738866e..33e3ee4f3383 100644
> > --- a/kernel/signal.c
> > +++ b/kernel/signal.c
> > @@ -1342,9 +1342,10 @@ force_sig_info_to_task(struct kernel_siginfo *info, struct task_struct *t,
> > }
> > /*
> > * Don't clear SIGNAL_UNKILLABLE for traced tasks, users won't expect
> > - * debugging to leave init killable.
> > + * debugging to leave init killable, unless it is intended to exit.
> > */
> > - if (action->sa.sa_handler == SIG_DFL && !t->ptrace)
> > + if (action->sa.sa_handler == SIG_DFL &&
> > + (!t->ptrace || (handler == HANDLER_EXIT)))
> > t->signal->flags &= ~SIGNAL_UNKILLABLE;
>
> You're changing the subclause:
>
> !t->ptrace
>
> to:
>
> (!t->ptrace || (handler == HANDLER_EXIT))
>
> which means that the change only affects cases where the process has a
> ptracer, right? That's not the scenario the commit message is talking
> about...
Sorry, yes, I was not as accurate as I should have been in the commit
log. I have changed it to:
Fatal SIGSYS signals (i.e. seccomp RET_KILL_* syscall filter actions)
were not being delivered to ptraced pid namespace init processes. Make
sure the SIGNAL_UNKILLABLE doesn't get set for these cases.
>
> > ret = send_signal(sig, info, t, PIDTYPE_PID);
> > spin_unlock_irqrestore(&t->sighand->siglock, flags);
> > --
> > 2.30.2
> >
--
Kees Cook
