Re: [PATCH] vt: Fix a missing-check bug in drivers/tty/vt/vt.c file of Linux 5.0.14

[Greg KH <gregkh@linuxfoundation.org>]

On Sun, May 12, 2019 at 04:49:39PM +0800, Gen Zhang wrote:
> On Sun, May 12, 2019 at 08:20:09AM +0200, Greg KH wrote:
> > Yes, that worked!  Now, can you resend it in a proper format that I can
> > apply it in?  (with changelog text, signed-off-by, etc.) as described in
> > Documentation/SubmittingPatches, I will be glad to review it after the
> > 5.2-rc1 release happens.
> > 
> > thanks,
> > 
> > greg k-h
> From: Gen Zhang <blackgod016574@gmail.com>
> Date: Sun, 11 May 2019 15:31:30 +0000
> Subject: [PATCH] vt: Fix a missing-check bug in drivers/tty/vt/vt.c file of Linux 5.0.14

Better, but no need for this to be in the body, just send it like any
other patch on the mailing list.

> 
> Hi,
> I found this missing-check bug in drivers/tty/vt/vt.c when I was examining the source code. 

That doesn't need to be in the changelog text.

> 
> 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. 

Properly wrap your lines at 72 columns please.

> 
> However, when there is a memory allocation error, kzalloc can  be failed. 
> 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 an error.
> 
> And this patch works in 5.1.1.

No need to say that.

> 
> Thank you!
> 
> Kind regards
> Gen

Or that :)


> 
> Signed-off-by: Gen Zhang <blackgod016574@gmail.com>
> ---
> --- drivers/tty/vt/vt.c
> +++ drivers/tty/vt/vt.c
> @@ -3349,10 +3349,14 @@ 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_cons[currcons].d || !vc)
> +			goto err_vc;

What about the other memory that was allocated?  You never free that.

>  		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 err_vc_screenbuf;

Same here, you are now leaking memory.

Did you test this patch out with a kmalloc function that can fail?  If
not, please try to do so.

thanks,

greg k-h