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Date: Thu, 10 Feb 2022 09:37:36 -0800 From: Kees Cook <keescook@...omium.org> To: Jann Horn <jannh@...gle.com> Cc: "Eric W. Biederman" <ebiederm@...ssion.com>, Robert Święcki <robert@...ecki.net>, stable@...r.kernel.org, Andy Lutomirski <luto@...capital.net>, Will Drewry <wad@...omium.org>, linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org Subject: Re: [PATCH 1/3] signal: HANDLER_EXIT should clear SIGNAL_UNKILLABLE 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@...omium.org> 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@...ecki.net> > > Suggested-by: "Eric W. Biederman" <ebiederm@...ssion.com> > > Fixes: 00b06da29cf9 ("signal: Add SA_IMMUTABLE to ensure forced siganls do not get changed") > > Cc: stable@...r.kernel.org > > Signed-off-by: Kees Cook <keescook@...omium.org> > > --- > > 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
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