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From: Greg KH <gregkh@linuxfoundation.org>
To: Gen Zhang <blackgod016574@gmail.com>
Cc: linux-kernel <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] vt: Fix a missing-check bug in drivers/tty/vt/vt.c file of Linux 5.0.14
Date: Mon, 13 May 2019 11:58:09 +0200	[thread overview]
Message-ID: <20190513095809.GA4588@kroah.com> (raw)
In-Reply-To: <20190513093730.GA4487@zhanggen-UX430UQ>

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@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
> 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

  reply	other threads:[~2019-05-13  9:58 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <CAAie0ar11_mPipN=d=mrgnVdEMO1Np0cCYdqcRfZrij_d-5zaQ@mail.gmail.com>
     [not found] ` <20190510051415.GA6073@kroah.com>
     [not found]   ` <CAAie0ao_O0hcUOuUf67oog+dSswdQRpAtX8NyQvDAr_XQr=xQg@mail.gmail.com>
2019-05-10 15:12     ` Greg KH
     [not found]       ` <CAAie0arnSxFvkNE1KSxD1a19_PQy03Q4RSiLZo9t7C9LeKkA9w@mail.gmail.com>
2019-05-11  6:07         ` Greg KH
2019-05-12  3:27           ` Gen Zhang
2019-05-12  6:20             ` Greg KH
2019-05-12  8:49               ` Gen Zhang
2019-05-13  7:36                 ` Greg KH
2019-05-13  9:37                   ` Gen Zhang
2019-05-13  9:58                     ` Greg KH [this message]
2019-05-13 11:33                       ` Gen Zhang
2019-05-16  9:07                       ` Gen Zhang

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