linux-kernel - Re: [PATCH] tty/n_hdlc: fix __might

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Date:   Thu, 10 Jan 2019 20:38:33 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>, jslaby@...e.com
Cc:     Paul Fulghum <paulkf@...rogate.com>,
        "linux-kernel@...r.kernel.org Mailing List" 
        <linux-kernel@...r.kernel.org>, Arnd Bergmann <arnd@...db.de>,
        Alan Cox <alan@...rguk.ukuu.org.uk>,
        syzbot <syzbot+c244af085a0159d22879@...kaller.appspotmail.com>,
        syzkaller-bugs@...glegroups.com
Subject: Re: [PATCH] tty/n_hdlc: fix __might_sleep warning

Hello, Greg.

We attempted a cleanup but we failed. Thus, will you apply this patch for now?

On 2019/01/02 5:28, Paul Fulghum wrote:
> Fix __might_sleep warning in tty/n_hdlc.c read due to copy_to_user call while current is TASK_INTERRUPTIBLE.
> This is a false positive since the code path does not depend on current state remaining TASK_INTERRUPTIBLE.
> The loop breaks out and sets TASK_RUNNING after calling copy_to_user. 
> This patch supresses the warning by setting TASK_RUNNING before calling copy_to_user.
> 
> [1] https://syzkaller.appspot.com/bug?id=17d5de7f1fcab794cb8c40032f893f52de899324
> 
> Signed-off-by: Paul Fulghum <paulkf@...rogate.com>
> Reported-by: syzbot <syzbot+c244af085a0159d22879@...kaller.appspotmail.com>
> Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> Cc: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
> Cc: Arnd Bergmann <arnd@...db.de>
> Cc: Alan Cox <alan@...rguk.ukuu.org.uk>
> —
> --- a/drivers/tty/n_hdlc.c	2018-12-23 15:55:59.000000000 -0800
> +++ b/drivers/tty/n_hdlc.c	2019-01-01 11:44:47.148153954 -0800
> @@ -597,6 +597,7 @@ static ssize_t n_hdlc_tty_read(struct tt
>  				/* too large for caller's buffer */
>  				ret = -EOVERFLOW;
>  			} else {
> +				__set_current_state(TASK_RUNNING);
>  				if (copy_to_user(buf, rbuf->buf, rbuf->count))
>  					ret = -EFAULT;
>  				else