This is a note to let you know that I've just added the patch titled

kernel/signal.c: protect the traced SIGNAL_UNKILLABLE tasks from SIGKILL

to the 4.4-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git%3Ba=su...

The filename of the patch is: kernel-signal.c-protect-the-traced-signal_unkillable-tasks-from-sigkill.patch and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let stable@vger.kernel.org know about it.

From 628c1bcba204052d19b686b5bac149a644cdb72e Mon Sep 17 00:00:00 2001

From: Oleg Nesterov oleg@redhat.com Date: Fri, 17 Nov 2017 15:30:01 -0800 Subject: kernel/signal.c: protect the traced SIGNAL_UNKILLABLE tasks from SIGKILL

From: Oleg Nesterov oleg@redhat.com

commit 628c1bcba204052d19b686b5bac149a644cdb72e upstream.

The comment in sig_ignored() says "Tracers may want to know about even ignored signals" but SIGKILL can not be reported to debugger and it is just wrong to return 0 in this case: SIGKILL should only kill the SIGNAL_UNKILLABLE task if it comes from the parent ns.

Change sig_ignored() to ignore ->ptrace if sig == SIGKILL and rely on sig_task_ignored().

SISGTOP coming from within the namespace is not really right too but at least debugger can intercept it, and we can't drop it here because this will break "gdb -p 1": ptrace_attach() won't work. Perhaps we will add another ->ptrace check later, we will see.

Link: http://lkml.kernel.org/r/20171103184206.GB21036@redhat.com Signed-off-by: Oleg Nesterov oleg@redhat.com Tested-by: Kyle Huey me@kylehuey.com Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Linus Torvalds torvalds@linux-foundation.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org

--- kernel/signal.c | 12 +++++++----- 1 file changed, 7 insertions(+), 5 deletions(-)

--- a/kernel/signal.c +++ b/kernel/signal.c @@ -88,13 +88,15 @@ static int sig_ignored(struct task_struc if (sigismember(&t->blocked, sig) || sigismember(&t->real_blocked, sig)) return 0;

- if (!sig_task_ignored(t, sig, force)) - return 0; - /* - * Tracers may want to know about even ignored signals. + * Tracers may want to know about even ignored signal unless it + * is SIGKILL which can't be reported anyway but can be ignored + * by SIGNAL_UNKILLABLE task. */ - return !t->ptrace; + if (t->ptrace && sig != SIGKILL) + return 0; + + return sig_task_ignored(t, sig, force); }

/*

Patches currently in stable-queue which might be from oleg@redhat.com are

queue-4.4/kernel-signal.c-remove-the-no-longer-needed-signal_unkillable-check-in-complete_signal.patch queue-4.4/kernel-signal.c-protect-the-signal_unkillable-tasks-from-sig_kernel_only-signals.patch queue-4.4/x86-kasan-write-protect-kasan-zero-shadow.patch queue-4.4/kernel-acct.c-fix-the-acct-needcheck-check-in-check_free_space.patch queue-4.4/kernel-signal.c-protect-the-traced-signal_unkillable-tasks-from-sigkill.patch