From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 640BDC433F5 for ; Mon, 20 Dec 2021 15:14:03 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S238948AbhLTPOC (ORCPT ); Mon, 20 Dec 2021 10:14:02 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:39630 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S239934AbhLTPMS (ORCPT ); Mon, 20 Dec 2021 10:12:18 -0500 Received: from ams.source.kernel.org (ams.source.kernel.org [IPv6:2604:1380:4601:e00::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id B96B4C08EB3F; Mon, 20 Dec 2021 06:56:40 -0800 (PST) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id 795F5B80EEB; Mon, 20 Dec 2021 14:56:39 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id C3C3AC36AE7; Mon, 20 Dec 2021 14:56:37 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1640012198; bh=QS3/dkB+tB/5IAh2e9vOTrOIW7Lz2+qYnejvi53vs0Q=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=MIj8rg51WlHEufs+OCihy9aHjv++Q7wjlmCdYA5yFmbBSIAPKAVYlo2prsFnlI6dl Aob+r71GknmCZP7aalap63Fq8WV1Jy9tF++FcwJincqlw9vOvOc/GQ2MW/MkRIPByp OqdKIdkO2AgdcTb2JYVJdVdAILwn4RX3cSiy3ipI= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, syzbot , Linus Torvalds , "Fabio M. De Francesco" , Tetsuo Handa , Jiri Slaby Subject: [PATCH 5.15 116/177] tty: n_hdlc: make n_hdlc_tty_wakeup() asynchronous Date: Mon, 20 Dec 2021 15:34:26 +0100 Message-Id: <20211220143043.982140657@linuxfoundation.org> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20211220143040.058287525@linuxfoundation.org> References: <20211220143040.058287525@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Tetsuo Handa commit 1ee33b1ca2b8dabfcc17198ffd049a6b55674a86 upstream. syzbot is reporting that an unprivileged user who logged in from tty console can crash the system using a reproducer shown below [1], for n_hdlc_tty_wakeup() is synchronously calling n_hdlc_send_frames(). ---------- #include #include int main(int argc, char *argv[]) { const int disc = 0xd; ioctl(1, TIOCSETD, &disc); while (1) { ioctl(1, TCXONC, 0); write(1, "", 1); ioctl(1, TCXONC, 1); /* Kernel panic - not syncing: scheduling while atomic */ } } ---------- Linus suspected that "struct tty_ldisc"->ops->write_wakeup() must not sleep, and Jiri confirmed it from include/linux/tty_ldisc.h. Thus, defer n_hdlc_send_frames() from n_hdlc_tty_wakeup() to a WQ context like net/nfc/nci/uart.c does. Link: https://syzkaller.appspot.com/bug?extid=5f47a8cea6a12b77a876 [1] Reported-by: syzbot Cc: stable Analyzed-by: Fabio M. De Francesco Suggested-by: Linus Torvalds Confirmed-by: Jiri Slaby Reviewed-by: Fabio M. De Francesco Signed-off-by: Tetsuo Handa Link: https://lore.kernel.org/r/40de8b7e-a3be-4486-4e33-1b1d1da452f8@i-love.sakura.ne.jp Signed-off-by: Greg Kroah-Hartman --- drivers/tty/n_hdlc.c | 23 ++++++++++++++++++++++- 1 file changed, 22 insertions(+), 1 deletion(-) --- a/drivers/tty/n_hdlc.c +++ b/drivers/tty/n_hdlc.c @@ -140,6 +140,8 @@ struct n_hdlc { struct n_hdlc_buf_list rx_buf_list; struct n_hdlc_buf_list tx_free_buf_list; struct n_hdlc_buf_list rx_free_buf_list; + struct work_struct write_work; + struct tty_struct *tty_for_write_work; }; /* @@ -154,6 +156,7 @@ static struct n_hdlc_buf *n_hdlc_buf_get /* Local functions */ static struct n_hdlc *n_hdlc_alloc(void); +static void n_hdlc_tty_write_work(struct work_struct *work); /* max frame size for memory allocations */ static int maxframe = 4096; @@ -210,6 +213,8 @@ static void n_hdlc_tty_close(struct tty_ wake_up_interruptible(&tty->read_wait); wake_up_interruptible(&tty->write_wait); + cancel_work_sync(&n_hdlc->write_work); + n_hdlc_free_buf_list(&n_hdlc->rx_free_buf_list); n_hdlc_free_buf_list(&n_hdlc->tx_free_buf_list); n_hdlc_free_buf_list(&n_hdlc->rx_buf_list); @@ -241,6 +246,8 @@ static int n_hdlc_tty_open(struct tty_st return -ENFILE; } + INIT_WORK(&n_hdlc->write_work, n_hdlc_tty_write_work); + n_hdlc->tty_for_write_work = tty; tty->disc_data = n_hdlc; tty->receive_room = 65536; @@ -335,6 +342,20 @@ check_again: } /* end of n_hdlc_send_frames() */ /** + * n_hdlc_tty_write_work - Asynchronous callback for transmit wakeup + * @work: pointer to work_struct + * + * Called when low level device driver can accept more send data. + */ +static void n_hdlc_tty_write_work(struct work_struct *work) +{ + struct n_hdlc *n_hdlc = container_of(work, struct n_hdlc, write_work); + struct tty_struct *tty = n_hdlc->tty_for_write_work; + + n_hdlc_send_frames(n_hdlc, tty); +} /* end of n_hdlc_tty_write_work() */ + +/** * n_hdlc_tty_wakeup - Callback for transmit wakeup * @tty: pointer to associated tty instance data * @@ -344,7 +365,7 @@ static void n_hdlc_tty_wakeup(struct tty { struct n_hdlc *n_hdlc = tty->disc_data; - n_hdlc_send_frames(n_hdlc, tty); + schedule_work(&n_hdlc->write_work); } /* end of n_hdlc_tty_wakeup() */ /**