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;a=summary
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@xxxxxxxxxxxxxxx> know about it.
>From 628c1bcba204052d19b686b5bac149a644cdb72e Mon Sep 17 00:00:00 2001
From: Oleg Nesterov <oleg@xxxxxxxxxx>
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@xxxxxxxxxx>
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@xxxxxxxxxx
Signed-off-by: Oleg Nesterov <oleg@xxxxxxxxxx>
Tested-by: Kyle Huey <me@xxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
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@xxxxxxxxxx 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