netdev - Re: [PATCH net] net: esp{4,6}: fix potential MTU calculation overflows

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Message-Id: <20130805.122723.934034495074719594.davem@davemloft.net>
Date:	Mon, 05 Aug 2013 12:27:23 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	dborkman@...hat.com
Cc:	netdev@...r.kernel.org, bpoirier@...e.de,
	steffen.klassert@...unet.com
Subject: Re: [PATCH net] net: esp{4,6}: fix potential MTU calculation
 overflows

From: Daniel Borkmann <dborkman@...hat.com>
Date: Mon,  5 Aug 2013 12:49:35 +0200

> Commit 91657eafb ("xfrm: take net hdr len into account for esp payload
> size calculation") introduced a possible interger overflow in
> esp{4,6}_get_mtu() handlers in case of x->props.mode equals
> XFRM_MODE_TUNNEL. Thus, the following expression will overflow
> 
>   unsigned int net_adj;
>   ...
>   <case ipv{4,6} XFRM_MODE_TUNNEL>
>          net_adj = 0;
>   ...
>   return ((mtu - x->props.header_len - crypto_aead_authsize(esp->aead) -
>            net_adj) & ~(align - 1)) + (net_adj - 2);
> 
> where (net_adj - 2) would be evaluated as <foo> + (0 - 2) in an unsigned
> context. Fix it by simply removing brackets as those operations here
> do not need to have special precedence.
> 
> Signed-off-by: Daniel Borkmann <dborkman@...hat.com>

Applied.
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