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: <20190513095809.GA4588@kroah.com>
Date:   Mon, 13 May 2019 11:58:09 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Gen Zhang <blackgod016574@...il.com>
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 05:37:41PM +0800, Gen Zhang wrote:
> 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.

You have to unwind the loop and free and uninitialize all of the other
things you just created as well.

> 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?

qemu should work just fine, I don't know what else to suggest.  Run it
on "real hardware" with a kmalloc function modified to fail this
allocation?

good luck!

greg k-h