From: Johan Hovold <johan@kernel.org>
To: Jiri Slaby <jslaby@suse.cz>
Cc: Gen Zhang <blackgod016574@gmail.com>, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] tty_io: Fix a missing-check bug in drivers/tty/tty_io.c
Date: Wed, 22 May 2019 12:29:00 +0200 [thread overview]
Message-ID: <20190522102900.GC2200@localhost> (raw)
In-Reply-To: <3a3db304-9725-6a90-65ac-dff09ef31aae@suse.cz>
On Wed, May 22, 2019 at 10:15:56AM +0200, Jiri Slaby wrote:
> On 22. 05. 19, 10:06, Gen Zhang wrote:
> > On Wed, May 22, 2019 at 06:25:36AM +0200, Jiri Slaby wrote:
> >> On 22. 05. 19, 3:40, Gen Zhang wrote:
> >>> In alloc_tty_struct(), tty->dev is assigned by tty_get_device(). And it
> >>> calls class_find_device(). And class_find_device() may return NULL.
> >>> And tty->dev is dereferenced in the following codes. When
> >>> tty_get_device() returns NULL, dereferencing this tty->dev null pointer
> >>> may cause the kernel go wrong. Thus we should check tty->dev.
Where do you see that the kernel is dereferencing tty->dev without
checking for NULL first? If you can find that, then that would indeed be
a bug that needs fixing.
> >>> Further, if tty_get_device() returns NULL, we should free tty and
> >>> return NULL.
> >>>
> >>> Signed-off-by: Gen Zhang <blackgod016574@gmail.com>
> >>>
> >>> ---
> >>> diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
> >>> index 033ac7e..1444b59 100644
> >>> --- a/drivers/tty/tty_io.c
> >>> +++ b/drivers/tty/tty_io.c
> >>> @@ -3008,6 +3008,10 @@ struct tty_struct *alloc_tty_struct(struct tty_driver *driver, int idx)
> >>> tty->index = idx;
> >>> tty_line_name(driver, idx, tty->name);
> >>> tty->dev = tty_get_device(tty);
> >>> + if (!tty->dev) {
> >>> + kfree(tty);
> >>> + return NULL;
> >>> + }
> >>
> >> This is incorrect, you introduced an ldisc reference leak.
> > Thanks for your reply, Jiri!
> > And what do you mean by an ldisc reference leak? I did't get the reason
> > of introducing it.
>
> Look at the top of alloc_tty_struct: there is tty_ldisc_init. If
> tty_get_device fails here, you have to call tty_ldisc_deinit. Better,
> you should add a failure-handling tail to this function and "goto" there.
>
> >> And can this happen at all?
> > I think tty_get_device() may happen to return NULL. Because it calls
> > class_find_device() and there's a chance class_find_device() returns
> > NULL.
>
> Sure, but can class_find_device return NULL in this tty case here?
Yes, it can and will and that's fine, not all ttys have a struct device
(e.g. ptys).
This patch is broken and should be dropped.
Johan
next prev parent reply other threads:[~2019-05-22 10:29 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-05-22 1:40 [PATCH] tty_io: Fix a missing-check bug in drivers/tty/tty_io.c Gen Zhang
2019-05-22 4:25 ` Jiri Slaby
2019-05-22 8:06 ` Gen Zhang
2019-05-22 8:15 ` Jiri Slaby
2019-05-22 10:29 ` Johan Hovold [this message]
2019-05-22 10:32 ` Jiri Slaby
2019-05-22 11:13 ` Gen Zhang
2019-05-22 11:19 ` Johan Hovold
2019-05-22 11:24 ` Gen Zhang
2019-05-22 11:18 ` Gen Zhang
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