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

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Message-ID: <20190513093730.GA4487@zhanggen-UX430UQ>
Date:   Mon, 13 May 2019 17:37:41 +0800
From:   Gen Zhang <blackgod016574@...il.com>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] vt: Fix a missing-check bug in drivers/tty/vt/vt.c file
 of Linux 5.0.14

On Mon, May 13, 2019 at 09:36:19AM +0200, Greg KH wrote:
> > Signed-off-by: Gen Zhang <blackgod016574@...il.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
Hi, Greg
1. I re-examined the source code.
For vc_cons[currcons].d and vc allocation fail, we may need to free
vc->vc_screenbuf from the previous loop. So kfree(vc->vc_screenbuf) 
need to be added to err_vc;
As for vc->vc_screenbuf allocation fail, I don't think there is other
memory need to be freed. Because in function con_init, there's no other 
allocation operations except this two kzalloc functions. And in
err_vc_screenbuf, vc_cons[currcons].d and vc is freed in the patch.

2. I tried to test this patch with a compiled kernel in QEMU but 
failed. Testing this is out of my skills. So is there any other ways
to test this patch?
Thanks
Gen