linux-kernel - Re: [PATCH -next 04/10] uml: Fix unsafe pid reference to foreground process group

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Date:	Fri, 17 Oct 2014 09:57:59 +0200
From:	Richard Weinberger <richard@....at>
To:	Peter Hurley <peter@...leysoftware.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
CC:	linux-serial@...r.kernel.org, linux-kernel@...r.kernel.org,
	Jiri Slaby <jslaby@...e.cz>,
	One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>,
	Jeff Dike <jdike@...toit.com>,
	user-mode-linux-devel@...ts.sourceforge.net
Subject: Re: [PATCH -next 04/10] uml: Fix unsafe pid reference to foreground
 process group

Am 16.10.2014 um 20:59 schrieb Peter Hurley:
> Although the tty core maintains a pid reference for the foreground
> process group, if the foreground process group is changed that
> pid reference is dropped. Thus, the pid reference used for signalling
> could become stale.
> 
> Safely obtain a pid reference to the foreground process group and
> release the reference after signalling is complete.
> 
> cc: Jeff Dike <jdike@...toit.com>
> cc: Richard Weinberger <richard@....at>
> cc: user-mode-linux-devel@...ts.sourceforge.net
> Signed-off-by: Peter Hurley <peter@...leysoftware.com>

Acked-by: Richard Weinberger <richard@....at>

> ---
>  arch/um/drivers/line.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/um/drivers/line.c b/arch/um/drivers/line.c
> index 8035145..6208702 100644
> --- a/arch/um/drivers/line.c
> +++ b/arch/um/drivers/line.c
> @@ -632,6 +632,7 @@ static irqreturn_t winch_interrupt(int irq, void *data)
>  	int fd = winch->fd;
>  	int err;
>  	char c;
> +	struct pid *pgrp;
>  
>  	if (fd != -1) {
>  		err = generic_read(fd, &c, NULL);
> @@ -657,7 +658,10 @@ static irqreturn_t winch_interrupt(int irq, void *data)
>  		if (line != NULL) {
>  			chan_window_size(line, &tty->winsize.ws_row,
>  					 &tty->winsize.ws_col);
> -			kill_pgrp(tty->pgrp, SIGWINCH, 1);
> +			pgrp = tty_get_pgrp(tty);
> +			if (pgrp)
> +				kill_pgrp(pgrp, SIGWINCH, 1);
> +			put_pid(pgrp);
>  		}
>  		tty_kref_put(tty);
>  	}
> 
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