linux-kernel - Re: [PATCH] Net, USB, Option, hso: Do not dereference NULL pointer

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Message-Id: <20110213.165608.149817059.davem@davemloft.net>
Date:	Sun, 13 Feb 2011 16:56:08 -0800 (PST)
From:	David Miller <davem@...emloft.net>
To:	jj@...osbits.net
Cc:	linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org,
	netdev@...r.kernel.org, gregkh@...e.de, j.dumon@...ion.com,
	f.aben@...ion.com, d.barow@...ion.com, ajb@...eresystems.co.uk
Subject: Re: [PATCH] Net, USB, Option, hso: Do not dereference NULL pointer

From: Jesper Juhl <jj@...osbits.net>
Date: Sun, 13 Feb 2011 22:15:35 +0100 (CET)

> In drivers/net/usb/hso.c::hso_create_bulk_serial_device() we have this 
> code:
> ...
> 	serial = kzalloc(sizeof(*serial), GFP_KERNEL);
> 	if (!serial)
> 		goto exit;
> ...
> exit:
> 	hso_free_tiomget(serial);
> ...
> hso_free_tiomget() directly dereferences its argument, which in the 
> example above is a NULL pointer, ouch.
> I could just add a 'if (serial)' test at the 'exit' label, but since most 
> freeing functions in the kernel accept NULL pointers (and it seems like 
> this was also assumed here) I opted to instead change 'hso_free_tiomget()' 
> so that it is safe to call it with a NULL argument. I also modified the 
> function to get rid of a pointles conditional before the call to 
> 'usb_free_urb()' since that function already tests for NULL itself - 
> besides fixing the NULL deref this change also buys us a few bytes in 
> size.
> Before:
> $ size drivers/net/usb/hso.o
>    text    data     bss     dec     hex filename
>   32200     592    9960   42752    a700 drivers/net/usb/hso.o
> After:
> $ size drivers/net/usb/hso.o
>    text    data     bss     dec     hex filename
>   32196     592    9960   42748    a6fc drivers/net/usb/hso.o
> 
> Signed-off-by: Jesper Juhl <jj@...osbits.net>

Applied.
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