linux-kernel - Re: [PATCH] tty: fix compat TIOCGSERIAL leaking uninitialized memory

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Message-ID: <20200224181532.GA109047@gmail.com>
Date:   Mon, 24 Feb 2020 10:15:32 -0800
From:   Eric Biggers <ebiggers@...nel.org>
To:     Jiri Slaby <jslaby@...e.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org, syzkaller-bugs@...glegroups.com,
        Al Viro <viro@...iv.linux.org.uk>
Subject: Re: [PATCH] tty: fix compat TIOCGSERIAL leaking uninitialized memory

On Mon, Feb 24, 2020 at 09:47:26AM +0100, Jiri Slaby wrote:
> On 24. 02. 20, 9:38, Eric Biggers wrote:
> > From: Eric Biggers <ebiggers@...gle.com>
> > 
> > Commit 77654350306a ("take compat TIOC[SG]SERIAL treatment into
> > tty_compat_ioctl()") changed the compat version of TIOCGSERIAL to start
> > copying a whole struct to userspace rather than individual fields, but
> > failed to initialize all padding and fields -- namely the hole after the
> > 'iomem_reg_shift' field, and the 'reserved' field.
> > 
> > Fix this by initializing the struct to zero.
> > 
> > Reported-by: syzbot+8da9175e28eadcb203ce@...kaller.appspotmail.com
> > Fixes: 77654350306a ("take compat TIOC[SG]SERIAL treatment into tty_compat_ioctl()")
> > Cc: <stable@...r.kernel.org> # v4.20+
> > Signed-off-by: Eric Biggers <ebiggers@...gle.com>
> > ---
> >  drivers/tty/tty_io.c | 1 +
> >  1 file changed, 1 insertion(+)
> > 
> > diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
> > index 1fcf7ad83dfa0..d24c250312edf 100644
> > --- a/drivers/tty/tty_io.c
> > +++ b/drivers/tty/tty_io.c
> > @@ -2731,6 +2731,7 @@ static int compat_tty_tiocgserial(struct tty_struct *tty,
> >  	struct serial_struct v;
> >  	int err;
> >  	memset(&v, 0, sizeof(struct serial_struct));
> > +	memset(&v32, 0, sizeof(struct serial_struct32));
> 
> sizeof(v32) please.
> 

Sure, I was trying to be consistent with the other line, but I'll just change
them both to sizeof.

- Eric