From: Osama Abdelkader <osama.abdelkader@gmail.com>
To: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Jiri Slaby <jirislaby@kernel.org>,
linux-kernel@vger.kernel.org, linux-serial@vger.kernel.org
Subject: Re: [PATCH] n_tty: add null check for tty->link in packet mode
Date: Mon, 23 Mar 2026 21:39:15 +0100 [thread overview]
Message-ID: <acGk84sMw-PwanbP@osama> (raw)
In-Reply-To: <2026031501-recolor-runaround-0ed5@gregkh>
On Sun, Mar 15, 2026 at 07:57:53AM +0100, Greg Kroah-Hartman wrote:
> On Sat, Mar 14, 2026 at 11:10:44PM +0100, Osama Abdelkader wrote:
> > Add null check for tty->link before dereferencing in n_tty_read and
> > n_tty_poll. When the pty master closes, tty->link can be NULL while
> > the slave is still reading, causing a null pointer dereference.
>
> How can that happen?
>
> > Signed-off-by: Osama Abdelkader <osama.abdelkader@gmail.com>
> > ---
> > drivers/tty/n_tty.c | 4 ++--
> > 1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/tty/n_tty.c b/drivers/tty/n_tty.c
> > index e6a0f5b40d0a..dc04b87364f6 100644
> > --- a/drivers/tty/n_tty.c
> > +++ b/drivers/tty/n_tty.c
> > @@ -2232,7 +2232,7 @@ static ssize_t n_tty_read(struct tty_struct *tty, struct file *file, u8 *kbuf,
> > add_wait_queue(&tty->read_wait, &wait);
> > while (nr) {
> > /* First test for status change. */
> > - if (packet && tty->link->ctrl.pktstatus) {
> > + if (packet && tty->link && tty->link->ctrl.pktstatus) {
> > u8 cs;
> > if (kb != kbuf)
> > break;
> > @@ -2444,7 +2444,7 @@ static __poll_t n_tty_poll(struct tty_struct *tty, struct file *file,
> > if (input_available_p(tty, 1))
> > mask |= EPOLLIN | EPOLLRDNORM;
> > }
> > - if (tty->ctrl.packet && tty->link->ctrl.pktstatus)
> > + if (tty->ctrl.packet && tty->link && tty->link->ctrl.pktstatus)
>
> What happens if link changes right after you test it? Where is the
> lock?
>
> And what changed to cause this to show up now?
>
> thanks,
>
> greg k-h
Hi Greg,
I was just thinking about null dereferencing possiblity in tty->link->ctrl.pktstatus. But, you are right
It’s reasonable to drop this patch and reopen it only if I get a solid reproducer or bug report.
BR,
Osama
prev parent reply other threads:[~2026-03-23 20:39 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-03-14 22:10 [PATCH] n_tty: add null check for tty->link in packet mode Osama Abdelkader
2026-03-15 6:57 ` Greg Kroah-Hartman
2026-03-23 20:39 ` Osama Abdelkader [this message]
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