The patch titled
signals: protect /sbin/init from unwanted signals more
has been added to the -mm tree. Its filename is
signals-protect-sbin-init-from-unwanted-signals-more.patch
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------------------------------------------------------
Subject: signals: protect /sbin/init from unwanted signals more
From: Oleg Nesterov <oleg@xxxxxxxxxx>
init ignores the SIG_DFL signals but we queue them anyway, including
SIGKILL. This is mostly OK, the signal will be dropped silently when
dequeued, but the pending SIGKILL has 2 bad implications:
- it implies fatal_signal_pending(), so we confuse things
like wait_for_completion_killable/lock_page_killable.
- for the sub-namespace inits, the pending SIGKILL can
mask (legacy_queue) the subsequent SIGKILL from the
parent namespace which must kill cinit reliably.
(preparation, cinits don't have SIGNAL_UNKILLABLE yet)
The patch can't help when init is ptraced, but ptracing of init is
not "safe" anyway.
Signed-off-by: Oleg Nesterov <oleg@xxxxxxxxxx>
Cc: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx>
Cc: Pavel Emelyanov <xemul@xxxxxxxxxx>
Cc: Roland McGrath <roland@xxxxxxxxxx>
Cc: "Serge E. Hallyn" <serue@xxxxxxxxxx>
Cc: Sukadev Bhattiprolu <sukadev@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
kernel/signal.c | 8 +++++++-
1 file changed, 7 insertions(+), 1 deletion(-)
diff -puN kernel/signal.c~signals-protect-sbin-init-from-unwanted-signals-more kernel/signal.c
--- a/kernel/signal.c~signals-protect-sbin-init-from-unwanted-signals-more
+++ a/kernel/signal.c
@@ -43,7 +43,13 @@ static struct kmem_cache *sigqueue_cache
static void __user *sig_handler(struct task_struct *t, int sig)
{
- return t->sighand->action[sig - 1].sa.sa_handler;
+ void __user *h = t->sighand->action[sig - 1].sa.sa_handler;
+
+ /* drop SIGKILL early to not confuse wait_xxx_killable/etc */
+ if (unlikely(t->signal->flags & SIGNAL_UNKILLABLE) && h == SIG_DFL)
+ h = SIG_IGN;
+
+ return h;
}
static int sig_handler_ignored(void __user *handler, int sig)
_
Patches currently in -mm which might be from oleg@xxxxxxxxxx are
forkc-cleanup-for-copy_sighand.patch
signals-protect-sbin-init-from-unwanted-signals-more.patch
signals-simplify-sig_ignored-pathes.patch
workqueues-kill-cpu_singlethread_map-use-get_cpu_mask-instead.patch
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