signal: HANDLER_EXIT should clear SIGNAL_UNKILLABLE

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.

Reported-by: Robert Święcki <robert@swiecki.net>
Suggested-by: "Eric W. Biederman" <ebiederm@xmission.com>
Fixes: 00b06da29cf9 ("signal: Add SA_IMMUTABLE to ensure forced siganls do not get changed")
Cc: stable@vger.kernel.org
Signed-off-by: Kees Cook <keescook@chromium.org>
Reviewed-by: "Eric W. Biederman" <ebiederm@xmission.com>
Link: https://lore.kernel.org/lkml/878rui8u4a.fsf@email.froward.int.ebiederm.org

diff --git a/kernel/signal.c b/kernel/signal.c
index 38602738866e3254186e4336b71544dacc787449..9b04631acde8fe8f866ea4d757e61a55f2bb76fe 100644 (file)
--- 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. But HANDLER_EXIT is always fatal.
         */
-       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;
        ret = send_signal(sig, info, t, PIDTYPE_PID);
        spin_unlock_irqrestore(&t->sighand->siglock, flags);