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Commit 10ab825b authored by Oleg Nesterov's avatar Oleg Nesterov Committed by Linus Torvalds
Browse files

change kernel threads to ignore signals instead of blocking them 



Currently kernel threads use sigprocmask(SIG_BLOCK) to protect against
signals.  This doesn't prevent the signal delivery, this only blocks
signal_wake_up().  Every "killall -33 kthreadd" means a "struct siginfo"
leak.

Change kthreadd_setup() to set all handlers to SIG_IGN instead of blocking
them (make a new helper ignore_signals() for that).  If the kernel thread
needs some signal, it should use allow_signal() anyway, and in that case it
should not use CLONE_SIGHAND.

Note that we can't change daemonize() (should die!) in the same way,
because it can be used along with CLONE_SIGHAND.  This means that
allow_signal() still should unblock the signal to work correctly with
daemonize()ed threads.

However, disallow_signal() doesn't block the signal any longer but ignores
it.

NOTE: with or without this patch the kernel threads are not protected from
handle_stop_signal(), this seems harmless, but not good.

Signed-off-by: default avatarOleg Nesterov <oleg@tv-sign.ru>
Acked-by: default avatar"Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 5de18d16

include/linux/sched.h

+1 −0
Original line number Diff line number Diff line
@@ -1317,6 +1317,7 @@ extern int in_egroup_p(gid_t); 


extern void proc_caches_init(void);

extern void flush_signals(struct task_struct *);

extern void ignore_signals(struct task_struct *);

extern void flush_signal_handlers(struct task_struct *, int force_default);

extern int dequeue_signal(struct task_struct *tsk, sigset_t *mask, siginfo_t *info);

kernel/exit.c

+1 −1
Original line number Diff line number Diff line
@@ -347,7 +347,7 @@ int disallow_signal(int sig) 
		return -EINVAL;



	spin_lock_irq(&current->sighand->siglock);

	sigaddset(&current->blocked, sig);

	current->sighand->action[(sig)-1].sa.sa_handler = SIG_IGN;

	recalc_sigpending();

	spin_unlock_irq(&current->sighand->siglock);

	return 0;

kernel/kthread.c

+3 −14
Original line number Diff line number Diff line
@@ -215,24 +215,13 @@ EXPORT_SYMBOL(kthread_stop); 
static __init void kthreadd_setup(void)

{

	struct task_struct *tsk = current;

	struct k_sigaction sa;

	sigset_t blocked;



	set_task_comm(tsk, "kthreadd");



	/* Block and flush all signals */

	sigfillset(&blocked);

	sigprocmask(SIG_BLOCK, &blocked, NULL);

	flush_signals(tsk);

	ignore_signals(tsk);



	/* SIG_IGN makes children autoreap: see do_notify_parent(). */

	sa.sa.sa_handler = SIG_IGN;

	sa.sa.sa_flags = 0;

	siginitset(&sa.sa.sa_mask, sigmask(SIGCHLD));

	do_sigaction(SIGCHLD, &sa, (struct k_sigaction *)0);



	set_user_nice(current, -5);

	set_cpus_allowed(current, CPU_MASK_ALL);

	set_user_nice(tsk, -5);

	set_cpus_allowed(tsk, CPU_MASK_ALL);

}



int kthreadd(void *unused)

kernel/signal.c

+10 −0
Original line number Diff line number Diff line
@@ -209,6 +209,16 @@ void flush_signals(struct task_struct *t) 
	spin_unlock_irqrestore(&t->sighand->siglock, flags);

}



void ignore_signals(struct task_struct *t)

{

	int i;



	for (i = 0; i < _NSIG; ++i)

		t->sighand->action[i].sa.sa_handler = SIG_IGN;



	flush_signals(t);

}



/*

 * Flush all handlers for a task.

 */