From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Cc: Jiri Slaby <jirislaby@kernel.org>,
syzbot <syzbot+06fa1063cca8163ea541@syzkaller.appspotmail.com>,
syzkaller-bugs@googlegroups.com,
Andrew Morton <akpm@linux-foundation.org>,
"Starke, Daniel" <daniel.starke@siemens.com>,
Lee Jones <lee@kernel.org>, Fedor Pchelkin <pchelkin@ispras.ru>,
linux-kernel@vger.kernel.org,
linux-serial <linux-serial@vger.kernel.org>
Subject: Re: [PATCH] tty: n_gsm: restrict tty devices to attach
Date: Wed, 24 Jan 2024 05:14:33 -0800 [thread overview]
Message-ID: <2024012418-passover-habitual-5a92@gregkh> (raw)
In-Reply-To: <42d17017-1d30-4c54-9c28-9d9ba2494e07@I-love.SAKURA.ne.jp>
On Wed, Jan 24, 2024 at 07:06:04PM +0900, Tetsuo Handa wrote:
> syzbot is reporting sleep in atomic context, for gsmld_write() is calling
> con_write() with spinlock held and IRQs disabled.
>
> Since n_gsm is designed to be used for serial port, reject attaching to
> virtual consoles and PTY devices, by checking tty's device major/minor
> numbers at gsmld_open().
>
> Link: https://www.kernel.org/doc/html/v6.7/driver-api/tty/n_gsm.html
> Reported-by: syzbot+06fa1063cca8163ea541@syzkaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=06fa1063cca8163ea541
> Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
> ---
> drivers/tty/n_gsm.c | 12 ++++++++++++
> 1 file changed, 12 insertions(+)
>
> diff --git a/drivers/tty/n_gsm.c b/drivers/tty/n_gsm.c
> index 4036566febcb..14581483af78 100644
> --- a/drivers/tty/n_gsm.c
> +++ b/drivers/tty/n_gsm.c
> @@ -3623,6 +3623,7 @@ static void gsmld_close(struct tty_struct *tty)
> static int gsmld_open(struct tty_struct *tty)
> {
> struct gsm_mux *gsm;
> + int major;
>
> if (!capable(CAP_NET_ADMIN))
> return -EPERM;
> @@ -3630,6 +3631,17 @@ static int gsmld_open(struct tty_struct *tty)
> if (tty->ops->write == NULL)
> return -EINVAL;
>
> + major = tty->driver->major;
> + /* Reject Virtual consoles */
> + if (major == 4 && tty->driver->minor_start == 1)
> + return -EINVAL;
> + /* Reject Unix98 PTY masters/slaves */
> + if (major >= 128 && major <= 143)
> + return -EINVAL;
> + /* Reject BSD PTY masters/slaves */
> + if (major >= 2 && major <= 3)
> + return -EINVAL;
That is a lot of hard-coded magic numbers, why aren't these defined
anywhere?
But really, this is only for fuzz testers, why can't they just not ever
bind this to a console? Why do we have to have these checks in the
kernel to prevent userspace from doing dumb things that no real
userspace will ever do?
thanks,
greg k-h
next prev parent reply other threads:[~2024-01-24 13:14 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-01-18 9:51 [syzbot] [dri?] BUG: scheduling while atomic in drm_atomic_helper_wait_for_flip_done syzbot
2024-01-18 14:18 ` Tetsuo Handa
2024-01-20 10:34 ` [PATCH] tty: vt: check for atomic context in con_write() Tetsuo Handa
2024-01-21 3:48 ` Hillf Danton
2024-01-21 11:34 ` Tetsuo Handa
2024-01-22 6:48 ` Jiri Slaby
2024-01-22 14:08 ` Tetsuo Handa
2024-01-24 10:06 ` [PATCH] tty: n_gsm: restrict tty devices to attach Tetsuo Handa
2024-01-24 13:14 ` Greg Kroah-Hartman [this message]
2024-02-03 13:45 ` Tetsuo Handa
2024-02-06 14:28 ` Greg Kroah-Hartman
2024-04-20 11:17 ` [syzbot] [dri?] BUG: scheduling while atomic in drm_atomic_helper_wait_for_flip_done Tetsuo Handa
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