From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Cc: Samo Pogacnik <samo_pogacnik@t-2.net>,
Petr Mladek <pmladek@suse.com>, Jiri Slaby <jirislaby@kernel.org>,
Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
Steven Rostedt <rostedt@goodmis.org>,
John Ogness <john.ogness@linutronix.de>,
linux-kernel@vger.kernel.org
Subject: Re: How to handle concurrent access to /dev/ttyprintk ?
Date: Mon, 12 Apr 2021 12:44:09 +0200 [thread overview]
Message-ID: <YHQkeZVs3pmyie9e@kroah.com> (raw)
In-Reply-To: <cd213843-45fe-2eac-4943-0906ab8d272b@i-love.sakura.ne.jp>
On Mon, Apr 12, 2021 at 07:39:04PM +0900, Tetsuo Handa wrote:
> What is the intended usage of /dev/ttyprintk ?
>
> It seems that drivers/char/ttyprintk.c was not designed to be opened by
> multiple processes. As a result, syzbot can trigger tty_warn() flooding
> enough to fire khungtaskd warning due to tty_port_close().
>
> Do we need to allow concurrent access to /dev/ttyprintk ?
> If we can't change /dev/ttyprintk exclusively open()able by only
> one thread, how to handle concurrent access to /dev/ttyprintk ?
Like any tty port, if you have multiple accesses, all bets are off and
hilarity ensues. Just don't do that and expect things to be working
well.
And trying to "open exclusive only" just does not work, the kernel can
not enforce that at all, sorry. Any driver that you see trying to do
that is trivial to work around in userspace, making the kernel code
pointless.
That being said, triggering warning messages is not good, we should fix
that where possible as what's preventing any other tty device from doing
the same?
thanks,
greg k-h
next prev parent reply other threads:[~2021-04-12 10:44 UTC|newest]
Thread overview: 43+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-03 4:14 [PATCH] tty: use printk_safe context at tty_msg() Tetsuo Handa
2021-04-03 6:52 ` kernel test robot
2021-04-03 10:11 ` [PATCH] printk: Make multiple inclusion of kernel/printk/internal.h safe Tetsuo Handa
2021-04-06 4:51 ` [PATCH] tty: use printk_safe context at tty_msg() Jiri Slaby
2021-04-06 5:31 ` Tetsuo Handa
2021-04-06 7:10 ` Greg Kroah-Hartman
2021-04-06 11:16 ` Tetsuo Handa
2021-04-06 13:42 ` Greg Kroah-Hartman
2021-04-06 15:10 ` Petr Mladek
2021-04-06 16:22 ` Tetsuo Handa
2021-04-06 19:10 ` Greg Kroah-Hartman
2021-04-07 9:20 ` Petr Mladek
2021-04-07 13:26 ` [PATCH v2] tty: use printk_deferred() " Tetsuo Handa
2021-04-07 13:48 ` Greg Kroah-Hartman
2021-04-07 14:24 ` Tetsuo Handa
2021-04-12 10:39 ` How to handle concurrent access to /dev/ttyprintk ? Tetsuo Handa
2021-04-12 10:44 ` Greg Kroah-Hartman [this message]
2021-04-12 11:25 ` Tetsuo Handa
2021-04-12 12:04 ` Greg Kroah-Hartman
2021-04-14 0:45 ` Tetsuo Handa
2021-04-14 11:11 ` Tetsuo Handa
2021-04-14 16:15 ` Samo Pogačnik
2021-04-15 0:22 ` [PATCH] ttyprintk: Add TTY hangup callback Tetsuo Handa
2021-04-18 11:16 ` Samo Pogačnik
2021-04-22 10:02 ` Greg Kroah-Hartman
2021-04-23 4:22 ` Jiri Slaby
2021-04-23 9:55 ` Samo Pogačnik
2021-04-23 10:12 ` Tetsuo Handa
2021-04-23 19:47 ` Samo Pogačnik
2021-04-24 1:16 ` Tetsuo Handa
2021-04-24 9:57 ` Samo Pogačnik
2021-04-26 10:00 ` Petr Mladek
2021-04-26 16:42 ` Samo Pogačnik
2021-04-27 10:08 ` Petr Mladek
2021-04-27 11:31 ` Samo Pogačnik
2021-04-23 10:28 ` Jiri Slaby
2021-04-23 12:23 ` [PATCH] ttyprintk: Add TTY port shutdown callback Samo Pogačnik
2021-04-12 12:41 ` How to handle concurrent access to /dev/ttyprintk ? Samo Pogačnik
2021-04-13 9:41 ` Petr Mladek
2021-04-13 11:10 ` Samo Pogačnik
2021-04-13 14:32 ` Petr Mladek
2021-04-13 15:22 ` Samo Pogačnik
2021-04-14 17:36 ` Petr Mladek
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=YHQkeZVs3pmyie9e@kroah.com \
--to=gregkh@linuxfoundation.org \
--cc=jirislaby@kernel.org \
--cc=john.ogness@linutronix.de \
--cc=linux-kernel@vger.kernel.org \
--cc=penguin-kernel@i-love.sakura.ne.jp \
--cc=pmladek@suse.com \
--cc=rostedt@goodmis.org \
--cc=samo_pogacnik@t-2.net \
--cc=sergey.senozhatsky@gmail.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox