From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 7383914A0A4; Tue, 25 Jun 2024 09:38:56 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1719308336; cv=none; b=eaNO+uFNZRUdtJTsMN1Gx2EYD4uWfkscB04DeJO9SLHGng2EMkWr6autPsv1EzhxiZAsn8h+ow8bj5axMex2EIBI/ASF5T2Dy6vkZUrfIUr/qfp6VHN/PPFALarX8eh5zAsw31muAJeYPjRHIOAO8QGbJcCNqtrga9lvNhKyiuA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1719308336; c=relaxed/simple; bh=fad+DEvk7M/iy4V61KoHFKQWK+V77ZivJCVJXgLFzjY=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=crItNmbTIPU1cGQ7fxYc8zEhLGeufL/dzbzDFCcvB/Er9XWcl4MCTQEiaszNjUpqZa2i75WCIGDRi2Wy1RK513KSeUtEbNQo3zyCkhN2aSLPEaY0pZS1JS9jQVXikQgA2kizn7/yxrNQnznfD43zuWkjdRrDXAPESWnvE0pYzF4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=KqfIoSAD; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="KqfIoSAD" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 88286C32781; Tue, 25 Jun 2024 09:38:55 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1719308335; bh=fad+DEvk7M/iy4V61KoHFKQWK+V77ZivJCVJXgLFzjY=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=KqfIoSADaPSp1qotO4I32DWNfr0vf7bDkwNOb90dFEorc2Ox5ymZwfEK94CJFynw/ +KEIBDHa5ABUV1bQ3ivyHbs9yY18+Eq4WL85YSiPcnIiYA+ohJidIVbV9rmQKzkfbm DUQI1f6sAF6UrYAnjnCfnGihOUJlJ9djeQP4qcyQ= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Tetsuo Handa , Jiri Slaby , Andrew Morton , Daniel Starke , syzbot , Linus Torvalds , Sasha Levin Subject: [PATCH 6.9 086/250] tty: add the option to have a tty reject a new ldisc Date: Tue, 25 Jun 2024 11:30:44 +0200 Message-ID: <20240625085551.368621044@linuxfoundation.org> X-Mailer: git-send-email 2.45.2 In-Reply-To: <20240625085548.033507125@linuxfoundation.org> References: <20240625085548.033507125@linuxfoundation.org> User-Agent: quilt/0.67 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.9-stable review patch. If anyone has any objections, please let me know. ------------------ From: Linus Torvalds [ Upstream commit 6bd23e0c2bb6c65d4f5754d1456bc9a4427fc59b ] ... and use it to limit the virtual terminals to just N_TTY. They are kind of special, and in particular, the "con_write()" routine violates the "writes cannot sleep" rule that some ldiscs rely on. This avoids the BUG: sleeping function called from invalid context at kernel/printk/printk.c:2659 when N_GSM has been attached to a virtual console, and gsmld_write() calls con_write() while holding a spinlock, and con_write() then tries to get the console lock. Tested-by: Tetsuo Handa Cc: Jiri Slaby Cc: Andrew Morton Cc: Daniel Starke Reported-by: syzbot Closes: https://syzkaller.appspot.com/bug?extid=dbac96d8e73b61aa559c Signed-off-by: Linus Torvalds Link: https://lore.kernel.org/r/20240423163339.59780-1-torvalds@linux-foundation.org Signed-off-by: Greg Kroah-Hartman Signed-off-by: Sasha Levin --- drivers/tty/tty_ldisc.c | 6 ++++++ drivers/tty/vt/vt.c | 10 ++++++++++ include/linux/tty_driver.h | 8 ++++++++ 3 files changed, 24 insertions(+) diff --git a/drivers/tty/tty_ldisc.c b/drivers/tty/tty_ldisc.c index 3f68e213df1f7..d80e9d4c974b4 100644 --- a/drivers/tty/tty_ldisc.c +++ b/drivers/tty/tty_ldisc.c @@ -545,6 +545,12 @@ int tty_set_ldisc(struct tty_struct *tty, int disc) goto out; } + if (tty->ops->ldisc_ok) { + retval = tty->ops->ldisc_ok(tty, disc); + if (retval) + goto out; + } + old_ldisc = tty->ldisc; /* Shutdown the old discipline. */ diff --git a/drivers/tty/vt/vt.c b/drivers/tty/vt/vt.c index 9b5b98dfc8b40..cd87e3d1291ed 100644 --- a/drivers/tty/vt/vt.c +++ b/drivers/tty/vt/vt.c @@ -3576,6 +3576,15 @@ static void con_cleanup(struct tty_struct *tty) tty_port_put(&vc->port); } +/* + * We can't deal with anything but the N_TTY ldisc, + * because we can sleep in our write() routine. + */ +static int con_ldisc_ok(struct tty_struct *tty, int ldisc) +{ + return ldisc == N_TTY ? 0 : -EINVAL; +} + static int default_color = 7; /* white */ static int default_italic_color = 2; // green (ASCII) static int default_underline_color = 3; // cyan (ASCII) @@ -3695,6 +3704,7 @@ static const struct tty_operations con_ops = { .resize = vt_resize, .shutdown = con_shutdown, .cleanup = con_cleanup, + .ldisc_ok = con_ldisc_ok, }; static struct cdev vc0_cdev; diff --git a/include/linux/tty_driver.h b/include/linux/tty_driver.h index 7372124fbf90b..dd4b31ce6d5d4 100644 --- a/include/linux/tty_driver.h +++ b/include/linux/tty_driver.h @@ -154,6 +154,13 @@ struct serial_struct; * * Optional. Called under the @tty->termios_rwsem. May sleep. * + * @ldisc_ok: ``int ()(struct tty_struct *tty, int ldisc)`` + * + * This routine allows the @tty driver to decide if it can deal + * with a particular @ldisc. + * + * Optional. Called under the @tty->ldisc_sem and @tty->termios_rwsem. + * * @set_ldisc: ``void ()(struct tty_struct *tty)`` * * This routine allows the @tty driver to be notified when the device's @@ -372,6 +379,7 @@ struct tty_operations { void (*hangup)(struct tty_struct *tty); int (*break_ctl)(struct tty_struct *tty, int state); void (*flush_buffer)(struct tty_struct *tty); + int (*ldisc_ok)(struct tty_struct *tty, int ldisc); void (*set_ldisc)(struct tty_struct *tty); void (*wait_until_sent)(struct tty_struct *tty, int timeout); void (*send_xchar)(struct tty_struct *tty, u8 ch); -- 2.43.0