linux-kernel - Re: tty: tty_open can return to userspace holding tty

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Message-ID: <497E28EA.8060504@msgid.tls.msk.ru>
Date:	Tue, 27 Jan 2009 00:19:38 +0300
From:	Michael Tokarev <mjt@....msk.ru>
To:	Eric Paris <eparis@...hat.com>
CC:	linux-kernel@...r.kernel.org, sgrubb@...hat.com,
	esandeen@...hat.com, sukadev@...ibm.com, alan@...rguk.ukuu.org.uk
Subject: Re: tty: tty_open can return to userspace holding tty_mutex

Eric Paris wrote:
> __tty_open could return (to userspace) holding the tty_mutex thanks to a
> regression introduced by 4a2b5fddd53b80efcb3266ee36e23b8de28e761a.  This was
> found by bisecting an fsfuzzer problem.  Admittedly I have no idea how it
> managed to tickle this 100% reliably, but it is clearly a regression and
> when hit leaves the box in a completely unusable state.  This patch lets
> the fsfuzzer test complete every time.

This should go to -stable too, right?
It's present in 2.6.28 (but not 2.6.27).

/mjt

> Signed-off-by: Eric Paris <eparis@...hat.com>
> 
> ---
>  drivers/char/tty_io.c |    4 +++-
>  1 files changed, 3 insertions(+), 1 deletions(-)
> 
> diff --git a/drivers/char/tty_io.c b/drivers/char/tty_io.c
> index d33e5ab..bc84e12 100644
> --- a/drivers/char/tty_io.c
> +++ b/drivers/char/tty_io.c
> @@ -1817,8 +1817,10 @@ got_driver:
>  		/* check whether we're reopening an existing tty */
>  		tty = tty_driver_lookup_tty(driver, inode, index);
>  
> -		if (IS_ERR(tty))
> +		if (IS_ERR(tty)) {
> +			mutex_unlock(&tty_mutex);
>  			return PTR_ERR(tty);
> +		}
>  	}
>  
>  	if (tty) {

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