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 9FD1FC7EE23 for ; Mon, 15 May 2023 16:48:01 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S242973AbjEOQsA (ORCPT ); Mon, 15 May 2023 12:48:00 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:52780 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S243013AbjEOQr6 (ORCPT ); Mon, 15 May 2023 12:47:58 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 123FB59EA for ; Mon, 15 May 2023 09:47:38 -0700 (PDT) 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 dfw.source.kernel.org (Postfix) with ESMTPS id 6784262912 for ; Mon, 15 May 2023 16:47:37 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 25828C433EF; Mon, 15 May 2023 16:47:35 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1684169256; bh=QyduOsEwRvEmvpGJPIOv46s04vhblpwmm6AXtDn+8MA=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=2kMaxjAJJkY3EwIqPoVf2Z81laRk9FNnquotr4++oRoihZ2D4ZTUsQp9MnLSlCFgB qFb6rp4SsxHjlb7yxUaqGz1US63i26ZXmek27Iqup2e2JbAhLIAm2KVsKEv0+K2gYL PC+tIRBeiRNgpB/duB4lLptmX6KbWTS/8pW7w2pg= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, =?UTF-8?q?Ilpo=20J=C3=A4rvinen?= Subject: [PATCH 4.19 185/191] tty: Prevent writing chars during tcsetattr TCSADRAIN/FLUSH Date: Mon, 15 May 2023 18:27:02 +0200 Message-Id: <20230515161714.211195755@linuxfoundation.org> X-Mailer: git-send-email 2.40.1 In-Reply-To: <20230515161707.203549282@linuxfoundation.org> References: <20230515161707.203549282@linuxfoundation.org> User-Agent: quilt/0.67 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org From: "Ilpo Järvinen" If userspace races tcsetattr() with a write, the drained condition might not be guaranteed by the kernel. There is a race window after checking Tx is empty before tty_set_termios() takes termios_rwsem for write. During that race window, more characters can be queued by a racing writer. Any ongoing transmission might produce garbage during HW's ->set_termios() call. The intent of TCSADRAIN/FLUSH seems to be preventing such a character corruption. If those flags are set, take tty's write lock to stop any writer before performing the lower layer Tx empty check and wait for the pending characters to be sent (if any). The initial wait for all-writers-done must be placed outside of tty's write lock to avoid deadlock which makes it impossible to use tty_wait_until_sent(). The write lock is retried if a racing write is detected. Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") Cc: stable@vger.kernel.org Signed-off-by: Ilpo Järvinen Link: https://lore.kernel.org/r/20230317113318.31327-2-ilpo.jarvinen@linux.intel.com Signed-off-by: Greg Kroah-Hartman (cherry picked from commit 094fb49a2d0d6827c86d2e0840873e6db0c491d2) Signed-off-by: Ilpo Järvinen Signed-off-by: Greg Kroah-Hartman --- drivers/tty/tty_io.c | 4 ++-- drivers/tty/tty_ioctl.c | 45 +++++++++++++++++++++++++++++++++------------ include/linux/tty.h | 2 ++ 3 files changed, 37 insertions(+), 14 deletions(-) --- a/drivers/tty/tty_io.c +++ b/drivers/tty/tty_io.c @@ -875,13 +875,13 @@ static ssize_t tty_read(struct file *fil return i; } -static void tty_write_unlock(struct tty_struct *tty) +void tty_write_unlock(struct tty_struct *tty) { mutex_unlock(&tty->atomic_write_lock); wake_up_interruptible_poll(&tty->write_wait, EPOLLOUT); } -static int tty_write_lock(struct tty_struct *tty, int ndelay) +int tty_write_lock(struct tty_struct *tty, int ndelay) { if (!mutex_trylock(&tty->atomic_write_lock)) { if (ndelay) --- a/drivers/tty/tty_ioctl.c +++ b/drivers/tty/tty_ioctl.c @@ -397,21 +397,42 @@ static int set_termios(struct tty_struct tmp_termios.c_ispeed = tty_termios_input_baud_rate(&tmp_termios); tmp_termios.c_ospeed = tty_termios_baud_rate(&tmp_termios); - ld = tty_ldisc_ref(tty); + if (opt & (TERMIOS_FLUSH|TERMIOS_WAIT)) { +retry_write_wait: + retval = wait_event_interruptible(tty->write_wait, !tty_chars_in_buffer(tty)); + if (retval < 0) + return retval; - if (ld != NULL) { - if ((opt & TERMIOS_FLUSH) && ld->ops->flush_buffer) - ld->ops->flush_buffer(tty); - tty_ldisc_deref(ld); - } + if (tty_write_lock(tty, 0) < 0) + goto retry_write_wait; - if (opt & TERMIOS_WAIT) { - tty_wait_until_sent(tty, 0); - if (signal_pending(current)) - return -ERESTARTSYS; - } + /* Racing writer? */ + if (tty_chars_in_buffer(tty)) { + tty_write_unlock(tty); + goto retry_write_wait; + } + + ld = tty_ldisc_ref(tty); + if (ld != NULL) { + if ((opt & TERMIOS_FLUSH) && ld->ops->flush_buffer) + ld->ops->flush_buffer(tty); + tty_ldisc_deref(ld); + } - tty_set_termios(tty, &tmp_termios); + if ((opt & TERMIOS_WAIT) && tty->ops->wait_until_sent) { + tty->ops->wait_until_sent(tty, 0); + if (signal_pending(current)) { + tty_write_unlock(tty); + return -ERESTARTSYS; + } + } + + tty_set_termios(tty, &tmp_termios); + + tty_write_unlock(tty); + } else { + tty_set_termios(tty, &tmp_termios); + } /* FIXME: Arguably if tmp_termios == tty->termios AND the actual requested termios was not tmp_termios then we may --- a/include/linux/tty.h +++ b/include/linux/tty.h @@ -480,6 +480,8 @@ extern void __stop_tty(struct tty_struct extern void stop_tty(struct tty_struct *tty); extern void __start_tty(struct tty_struct *tty); extern void start_tty(struct tty_struct *tty); +void tty_write_unlock(struct tty_struct *tty); +int tty_write_lock(struct tty_struct *tty, int ndelay); extern int tty_register_driver(struct tty_driver *driver); extern int tty_unregister_driver(struct tty_driver *driver); extern struct device *tty_register_device(struct tty_driver *driver,