linux-kernel - Re: [PATCH] serial: sh-sci: Fix use-after-free on subsequent port startup

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Date:   Tue, 17 Jul 2018 14:17:53 +0200
From:   Simon Horman <horms@...ge.net.au>
To:     Geert Uytterhoeven <geert+renesas@...der.be>
Cc:     Chris Brandt <chris.brandt@...esas.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jslaby@...e.com>, linux-serial@...r.kernel.org,
        linux-renesas-soc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] serial: sh-sci: Fix use-after-free on subsequent port
 startup

On Tue, Jul 17, 2018 at 10:58:10AM +0200, Geert Uytterhoeven wrote:
> sci_request_irq() checks port->irqstr[j] for a NULL pointer, to decide
> if a fallback interrupt name string should be allocated or not.
> 
> While this string is freed during port shutdown, the pointer is not
> zeroed.  Hence on a subsequent startup of the port, it will still be
> pointing to the freed memory, leading to e.g.
> 
>     WARNING: CPU: 0 PID: 404 at fs/proc/generic.c:388 __proc_create+0xbc/0x260
>     name len 0
> 
> or to a crash (the latter is more likely with CONFIG_DEBUG_SLAB=y, due
> to the poisoning of freed memory).
> 
> Instead of zeroeing the pointer at multiple places, preinitialize
> port->irqstr[j] to zero to fix this.
> 
> Fixes: 8b0bbd956228ae87 ("serial: sh-sci: Add support for R7S9210")
> Signed-off-by: Geert Uytterhoeven <geert+renesas@...der.be>

Reviewed-by: Simon Horman <horms+renesas@...ge.net.au>