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From: Gen Zhang <blackgod016574@gmail.com>
To: Nicolas Pitre <nico@fluxnic.net>
Cc: linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2] vt: Fix a missing-check bug in drivers/tty/vt/vt.c
Date: Wed, 22 May 2019 16:10:29 +0800	[thread overview]
Message-ID: <20190522081029.GB5109@zhanggen-UX430UQ> (raw)
In-Reply-To: <nycvar.YSQ.7.76.1905212218090.1558@knanqh.ubzr>

On Tue, May 21, 2019 at 10:43:11PM -0400, Nicolas Pitre wrote:
> On Tue, 21 May 2019, Gen Zhang wrote:
> 
> > On Tue, May 21, 2019 at 12:30:38AM -0400, Nicolas Pitre wrote:
> > > Now imagine that MIN_NR_CONSOLES is defined to 10 instead of 1.
> > > 
> > > What happens with allocated memory if the err_vc condition is met on the 
> > > 5th loop?
> > Yes, vc->vc_screenbuf from the last loop is still not freed, right? I
> > don't have idea to solve this one. Could please give some advice? Since
> > we have to consider the err_vc condition.
> > 
> > > If err_vc_screenbuf condition is encountered on the 5th loop (curcons = 
> > > 4), what is the value of vc_cons[4].d? Isn't it the same as vc that you 
> > > just freed?
> > > 
> > > 
> > > Nicolas
> > Thanks for your explaination! You mean a double free situation may 
> > happen, right? But in vc_allocate() there is also such a kfree(vc) and 
> > vc_cons[currcons].d = NULL operation. This situation is really confusing
> > me.
> 
> What you could do is something that looks like:
> 
> 	for (currcons = 0; currcons < MIN_NR_CONSOLES; currcons++) {
> 		vc_cons[currcons].d = vc = kzalloc(...);
> 		if (!vc)
> 			goto fail1;
> 		...
> 		vc->vc_screenbuf = kzalloc(...);
> 		if (!vc->vc_screenbuf)
> 			goto fail2;
> 		...
> 
> 	return 0;
> 
> 	/* free already allocated memory on error */
> fail1:
> 	while (curcons > 0) {
> 		curcons--;
> 		kfree(vc_cons[currcons].d->vc_screenbuf);
> fail2:
> 		kfree(vc_cons[currcons].d);
> 		vc_cons[currcons].d = NULL;
> 	}
> 	console_unlock();
> 	return -ENOMEM;
> 
> 
> Nicolas
Thanks for your patient explaination, Nicolas!
I will work on it and resubmit it.
Thanks
Gen

  reply	other threads:[~2019-05-22  8:10 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-05-21  2:29 Gen Zhang
2019-05-21  2:55 ` Nicolas Pitre
2019-05-21  3:09   ` Gen Zhang
2019-05-21  3:26     ` Nicolas Pitre
2019-05-21  4:00       ` Gen Zhang
2019-05-21  4:30         ` Nicolas Pitre
2019-05-21  7:39           ` Gen Zhang
2019-05-22  2:43             ` Nicolas Pitre
2019-05-22  8:10               ` Gen Zhang [this message]
2019-05-22 12:19               ` [PATCH v3] " Gen Zhang
2019-05-22 14:18                 ` Nicolas Pitre
2019-05-24  2:27                   ` [PATCH v3] vt: Fix a missing-check bug in con_init() Gen Zhang
2019-05-21  3:21   ` [PATCH v3] vt: Fix a missing-check bug in drivers/tty/vt/vt.c Gen Zhang
2019-05-21  6:46     ` Oleksandr Natalenko

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