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Date:   Wed, 22 May 2019 06:25:36 +0200
From:   Jiri Slaby <jslaby@...e.cz>
To:     Gen Zhang <blackgod016574@...il.com>
Cc:     linux-kernel@...r.kernel.org
Subject: Re: [PATCH] tty_io: Fix a missing-check bug in drivers/tty/tty_io.c

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.
> Further, if tty_get_device() returns NULL, we should free tty and 
> return NULL.
> 
> Signed-off-by: Gen Zhang <blackgod016574@...il.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.

And can this happen at all?

thanks,
-- 
js
suse labs

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