From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from www262.sakura.ne.jp (www262.sakura.ne.jp [202.181.97.72]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 507142F2D; Sat, 20 Jan 2024 10:34:31 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=202.181.97.72 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1705746874; cv=none; b=Hqm13JOiPkBTH7IknfihmNOh584GOXNTdy1OvjKWNxU3NTDTwgMvzRUewcE6SCqJ8M38plfg0dDtTv/Ux0D98YqCc/GFXOEizEHr3OusNqQtl0QSZhZjde9DO8nYJZ8+tNOtebPSunJLeZe6nO1vdy6tP4ZQRlmWSrtg3hu/4ZQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1705746874; c=relaxed/simple; bh=MhFgpNUMuNHG64flCLc5tUHSf5b5DIG7JaB6eZIoyk4=; h=Message-ID:Date:MIME-Version:Subject:From:To:Cc:References: In-Reply-To:Content-Type; b=mYZsqC1pZMtN2pKNJAG/MZ1p0/trGYUDW2JuXBxHzfyg/yoeJwefQWuWhWldMncM+uOR7GRRYkCvpT49G+GnEUnDiJSEo6IikoJe4FCqu2UUJXLU0LJSNoOfCI53UvQfixU0LvziKTYkOD6+erbjgU5OR7fVtbw+EThwk6o/+1s= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=I-love.SAKURA.ne.jp; spf=none smtp.mailfrom=I-love.SAKURA.ne.jp; arc=none smtp.client-ip=202.181.97.72 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=I-love.SAKURA.ne.jp Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=I-love.SAKURA.ne.jp Received: from fsav414.sakura.ne.jp (fsav414.sakura.ne.jp [133.242.250.113]) by www262.sakura.ne.jp (8.15.2/8.15.2) with ESMTP id 40KAY1hh090240; Sat, 20 Jan 2024 19:34:01 +0900 (JST) (envelope-from penguin-kernel@I-love.SAKURA.ne.jp) Received: from www262.sakura.ne.jp (202.181.97.72) by fsav414.sakura.ne.jp (F-Secure/fsigk_smtp/550/fsav414.sakura.ne.jp); Sat, 20 Jan 2024 19:34:01 +0900 (JST) X-Virus-Status: clean(F-Secure/fsigk_smtp/550/fsav414.sakura.ne.jp) Received: from [192.168.1.6] (M106072142033.v4.enabler.ne.jp [106.72.142.33]) (authenticated bits=0) by www262.sakura.ne.jp (8.15.2/8.15.2) with ESMTPSA id 40KAY13L090233 (version=TLSv1.2 cipher=AES256-GCM-SHA384 bits=256 verify=NO); Sat, 20 Jan 2024 19:34:01 +0900 (JST) (envelope-from penguin-kernel@I-love.SAKURA.ne.jp) Message-ID: <9cd9d3eb-418f-44cc-afcf-7283d51252d6@I-love.SAKURA.ne.jp> Date: Sat, 20 Jan 2024 19:34:02 +0900 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: [PATCH] tty: vt: check for atomic context in con_write() Content-Language: en-US From: Tetsuo Handa To: syzbot , syzkaller-bugs@googlegroups.com, Greg Kroah-Hartman , Jiri Slaby , Andrew Morton Cc: linux-kernel@vger.kernel.org, linux-serial References: <00000000000039f237060f354ef7@google.com> <83414cb6-df16-4b6d-92e3-d54d22ba26cc@I-love.SAKURA.ne.jp> In-Reply-To: <83414cb6-df16-4b6d-92e3-d54d22ba26cc@I-love.SAKURA.ne.jp> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit syzbot is reporting sleep in atomic context, for gsmld_write() is calling con_write() with spinlock held and IRQs disabled. Since include/linux/tty_ldisc.h says that "struct tty_ldisc_ops"->write (e.g. gsmld_write()) is allowed to sleep and include/linux/tty_driver.h says that "struct tty_operations"->write (e.g. con_write()) is not allowed to sleep, we should handle this problem on the con_write() side. It seems that "Andrew Morton: console locking merge" in 2.4.10-pre11 added in_interrupt() check to do_con_write()/con_put_char()/con_flush_chars() in order to handle exceptional caller. Since include/linux/preempt.h says that in_atomic() cannot know about held spinlocks in non-preemptible kernels, but gsmld_write() is calling con_write() with IRQs disabled, we can add irqs_disabled() check to do_con_write()/con_flush_chars() in order to handle this case. Though, I'm not sure whether returning the bytes to write is appropriate behavior when do_con_write() can't work... Reported-by: syzbot+06fa1063cca8163ea541@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=06fa1063cca8163ea541 Signed-off-by: Tetsuo Handa --- drivers/tty/vt/vt.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/drivers/tty/vt/vt.c b/drivers/tty/vt/vt.c index 156efda7c80d..0d3d602ae147 100644 --- a/drivers/tty/vt/vt.c +++ b/drivers/tty/vt/vt.c @@ -2856,7 +2856,7 @@ static int do_con_write(struct tty_struct *tty, const u8 *buf, int count) struct vt_notifier_param param; bool rescan; - if (in_interrupt()) + if (in_interrupt() || irqs_disabled()) return count; console_lock(); @@ -3314,7 +3314,7 @@ static void con_flush_chars(struct tty_struct *tty) { struct vc_data *vc; - if (in_interrupt()) /* from flush_to_ldisc */ + if (in_interrupt() || irqs_disabled()) /* from flush_to_ldisc */ return; /* if we race with con_close(), vt may be null */ -- 2.18.4