From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: Osama Abdelkader <osama.abdelkader@gmail.com>
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: Sun, 15 Mar 2026 07:57:53 +0100 [thread overview]
Message-ID: <2026031501-recolor-runaround-0ed5@gregkh> (raw)
In-Reply-To: <20260314221044.148442-1-osama.abdelkader@gmail.com>
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
next prev parent reply other threads:[~2026-03-15 6:58 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 [this message]
2026-03-23 20:39 ` Osama Abdelkader
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