linux-kernel - Re: [PATCH] tty:vt: Add check the return value of kzalloc to avoid oops

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Message-ID: <20190919092933.GA2684163@kroah.com>
Date:   Thu, 19 Sep 2019 11:29:33 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Xiaoming Ni <nixiaoming@...wei.com>
Cc:     penberg@...helsinki.fi, jslaby@...e.com, nico@...xnic.net,
        textshell@...uujin.de, sam@...nborg.org, daniel.vetter@...ll.ch,
        mpatocka@...hat.com, ghalat@...hat.com,
        linux-kernel@...r.kernel.org, yangyingliang@...wei.com,
        yuehaibing@...wei.com, zengweilin@...wei.com
Subject: Re: [PATCH] tty:vt: Add check the return value of kzalloc to avoid
 oops

On Thu, Sep 19, 2019 at 05:18:15PM +0800, Xiaoming Ni wrote:
> Using kzalloc() to allocate memory in function con_init(), but not
> checking the return value, there is a risk of null pointer references
> oops.
> 
> Signed-off-by: Xiaoming Ni <nixiaoming@...wei.com>

We keep having this be "reported" :(

> ---
>  drivers/tty/vt/vt.c | 18 ++++++++++++++++++
>  1 file changed, 18 insertions(+)
> 
> diff --git a/drivers/tty/vt/vt.c b/drivers/tty/vt/vt.c
> index 34aa39d..db83e52 100644
> --- a/drivers/tty/vt/vt.c
> +++ b/drivers/tty/vt/vt.c
> @@ -3357,15 +3357,33 @@ 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 (unlikely(!vc)) {
> +			pr_warn("%s:failed to allocate memory for the %u vc\n",
> +					__func__, currcons);
> +			break;
> +		}

At init, this really can not happen.  Have you see it ever happen?

>  		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 (unlikely(!vc->vc_screenbuf)) {

Never use likely/unlikely unless you can actually measure the speed
difference.  For something like this, the compiler will always get it
right without you having to do anything.

And again, how can this fail?  Have you seen it fail?

> +			pr_warn("%s:failed to allocate memory for the %u vc_screenbuf\n",
> +					__func__, currcons);
> +			visual_deinit(vc);
> +			tty_port_destroy(&vc->port);
> +			kfree(vc);
> +			vc_cons[currcons].d = NULL;
> +			break;
> +		}
>  		vc_init(vc, vc->vc_rows, vc->vc_cols,
>  			currcons || !vc->vc_sw->con_save_screen);
>  	}
>  	currcons = fg_console = 0;
>  	master_display_fg = vc = vc_cons[currcons].d;
> +	if (unlikely(!vc)) {

Again, never use likely/unlikely unless you can measure it.

thanks,

greg k-h