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Subject[PATCH 3.18 04/46] kernel/signal.c: protect the traced SIGNAL_UNKILLABLE tasks from SIGKILL
3.18-stable review patch.  If anyone has any objections, please let me know.


From: Oleg Nesterov <>

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

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.

Signed-off-by: Oleg Nesterov <>
Tested-by: Kyle Huey <>
Signed-off-by: Andrew Morton <>
Signed-off-by: Linus Torvalds <>
Signed-off-by: Greg Kroah-Hartman <>

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
- return !t->ptrace;
+ if (t->ptrace && sig != SIGKILL)
+ return 0;
+ return sig_task_ignored(t, sig, force);


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