linux-kernel - Re: [PATCH v2] vt: Fix a missing-check bug in drivers/tty/vt/vt.c

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Message-ID: <20190521073901.GF5263@zhanggen-UX430UQ>
Date:   Tue, 21 May 2019 15:39:01 +0800
From:   Gen Zhang <blackgod016574@...il.com>
To:     Nicolas Pitre <nico@...xnic.net>
Cc:     linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] vt: Fix a missing-check bug in drivers/tty/vt/vt.c

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.
Thanks
Gen