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Date: Thu, 7 Jan 2016 07:33:10 -0800 From: Greg Kroah-Hartman <gregkh@...uxfoundation.org> To: Mateusz Guzik <mguzik@...hat.com> Cc: Jiri Slaby <jslaby@...e.com>, stable@...r.kernel.org, linux-kernel@...r.kernel.org, security@...nel.org, milos@...hat.com Subject: Re: [PATCH] tty: plug a use-after-free in TIOCGETD ioctl On Thu, Jan 07, 2016 at 03:58:00PM +0100, Mateusz Guzik wrote: > When the line discipline is being changed, the old one is freed. > However, the handler for TIOCGETD would dereference it without taking > any locks, in effect possibly reading freed memory. > > Line discipline changes are protected with tty lock. Use it on reader > side as well. > > CVE: CVE-2016-0723 Why a cve tag? > Found-by: Milos Vyletel <milos@...hat.com> > Signed-off-by: Mateusz Guzik <mguzik@...hat.com> > --- > drivers/tty/tty_io.c | 23 ++++++++++++++++++++++- > 1 file changed, 22 insertions(+), 1 deletion(-) > > diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c > index 892c923..1b10469 100644 > --- a/drivers/tty/tty_io.c > +++ b/drivers/tty/tty_io.c > @@ -2626,6 +2626,27 @@ static int tiocgsid(struct tty_struct *tty, struct tty_struct *real_tty, pid_t _ > } > > /** > + * tiocgetd - get line discipline > + * @tty: tty device > + * @p: pointer to returned line discipline > + * > + * Get the line discipline associated with the tty. > + * > + * Locking: none > + */ > + > +static int tiocgetd(struct tty_struct *tty, int __user *p) > +{ > + int ldisc; > + > + tty_lock(tty); > + ldisc = tty->ldisc->ops->num; > + tty_unlock(tty); > + > + return put_user(ldisc, p); Does this really protect anything? What is preventing ldisc from going away right after the tty_unlock call? And how are you able to trigger the tty to go away while the file is still held open and this ioctl is being called? thanks, greg k-h -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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