linux-kernel - Re: [PATCH 1/1] tty: n_gsm: Avoid sleeping during .write() whilst atomic

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Message-ID: <20231005114632.GA681678@google.com>
Date:   Thu, 5 Oct 2023 12:46:32 +0100
From:   Lee Jones <lee@...nel.org>
To:     "Starke, Daniel" <daniel.starke@...mens.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Fedor Pchelkin <pchelkin@...ras.ru>,
        Jiri Slaby <jirislaby@...nel.org>,
        "linux-serial@...r.kernel.org" <linux-serial@...r.kernel.org>,
        "syzbot+5f47a8cea6a12b77a876@...kaller.appspotmail.com" 
        <syzbot+5f47a8cea6a12b77a876@...kaller.appspotmail.com>
Subject: Re: [PATCH 1/1] tty: n_gsm: Avoid sleeping during .write() whilst
 atomic

On Thu, 05 Oct 2023, Starke, Daniel wrote:

> > > Would something like this tick that box?
> > > 
> > > diff --git a/drivers/tty/n_gsm.c b/drivers/tty/n_gsm.c index 
> > > 1f3aba607cd51..5c1d2fcd5d9e2 100644
> > > --- a/drivers/tty/n_gsm.c
> > > +++ b/drivers/tty/n_gsm.c
> > > @@ -3716,6 +3716,10 @@ static ssize_t gsmld_write(struct tty_struct *tty, struct file *file,
> > >         if (!gsm)
> > >                 return -ENODEV;
> > >  
> > > +       /* The GSM line discipline does not support binding to console */
> > > +       if (strncmp(tty->name, "tty", 3))
> > > +               return -EINVAL;
> > 
> > No, that's not going to work, some consoles do not start with "tty" :(

Ah, you mean there are others that we need to consider?

I was just covering off con_write() from drivers/tty/vt/vt.c.

Does anyone have a counter proposal?

> Also, I would recommend exiting as early as possible. E.g. in gsmld_open().

Good suggestion.

> And please retain support for real serial devices (e.g. ttyS, ttyUSB,
> ttyACM, ...).

Okay, so it's "tty{0-9}*$" that should be excluded?

Plus others that Greg alluded to?

Is there a definitive accept / reject list?

-- 
Lee Jones [李琼斯]