linux-kernel - Re: [PATCH v3] vt: Fix a missing-check bug in drivers/tty/vt/vt.c

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Date:   Wed, 22 May 2019 10:18:54 -0400 (EDT)
From:   Nicolas Pitre <nico@...xnic.net>
To:     Gen Zhang <blackgod016574@...il.com>
cc:     linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] vt: Fix a missing-check bug in drivers/tty/vt/vt.c

On Wed, 22 May 2019, Gen Zhang wrote:

> In function con_init(), the pointer variable vc_cons[currcons].d, vc and
> vc->vc_screenbuf is allocated a memory space via kzalloc(). And they are
> used in the following codes.
> However, when there is a memory allocation error, kzalloc() can fail.
> Thus null pointer (vc_cons[currcons].d, vc and vc->vc_screenbuf)
> dereference may happen. And it will cause the kernel to crash. Therefore,
> we should check return value and handle the error.
> Further, since the allcoation is in a loop, we should free all the 
> allocated memory in a loop.
> 
> Signed-off-by: Gen Zhang <blackgod016574@...il.com>

Reviewed-by: Nicolas Pitre <nico@...xnic.net>


> 
> ---
> diff --git a/drivers/tty/vt/vt.c b/drivers/tty/vt/vt.c
> index fdd12f8..d50f68f 100644
> --- a/drivers/tty/vt/vt.c
> +++ b/drivers/tty/vt/vt.c
> @@ -3350,10 +3350,14 @@ static int __init con_init(void)
>  
>  	for (currcons = 0; currcons < MIN_NR_CONSOLES; currcons++) {
>  		vc_cons[currcons].d = vc = kzalloc(sizeof(struct vc_data), GFP_NOWAIT);
> +		if (!vc)
> +			goto fail1;
>  		INIT_WORK(&vc_cons[currcons].SAK_work, vc_SAK);
>  		tty_port_init(&vc->port);
>  		visual_init(vc, currcons, 1);
>  		vc->vc_screenbuf = kzalloc(vc->vc_screenbuf_size, GFP_NOWAIT);
> +		if (!vc->vc_screenbuf)
> +			goto fail2;
>  		vc_init(vc, vc->vc_rows, vc->vc_cols,
>  			currcons || !vc->vc_sw->con_save_screen);
>  	}
> @@ -3375,6 +3379,16 @@ static int __init con_init(void)
>  	register_console(&vt_console_driver);
>  #endif
>  	return 0;
> +fail1:
> +	while (currcons > 0) {
> +		currcons--;
> +		kfree(vc_cons[currcons].d->vc_screenbuf);
> +fail2:
> +		kfree(vc_cons[currcons].d);
> +		vc_cons[currcons].d = NULL;
> +	}
> +	console_unlock();
> +	return -ENOMEM;
>  }
>  console_initcall(con_init);
>  
> ---
>