netdev - Re: [PATCH 2/2] ppp_generic: linearise skbs before passing them to pppd

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Date:	Sun, 02 May 2010 23:27:11 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	simon@...e.lp0.eu
Cc:	netdev@...r.kernel.org, paulus@...ba.org, linux-ppp@...r.kernel.org
Subject: Re: [PATCH 2/2] ppp_generic: linearise skbs before passing them to
 pppd

From: Simon Arlott <simon@...e.lp0.eu>
Date: Fri, 30 Apr 2010 19:41:45 +0100

> Frequently when using PPPoE with an interface MTU greater than 1500,
> the skb is likely to be non-linear. If the skb needs to be passed to
> pppd then the skb must be linearised first.
> 
> The previous commit fixes an issue with accidentally sending skbs
> to pppd based on an invalid read of the protocol type. When that
> error occurred pppd was reading invalid skb data too.
> 
> Signed-off-by: Simon Arlott <simon@...e.lp0.eu>

Don't propagate stupidity.

The real problem is that ppp_read() can't handle non-linear SKBs, so
fix that instead.  The easiest way to do that is to put a "struct
iovec iov;" on ppp_read()'s stack, fill it in with ther user buffer
pointer and length, then use that to call
skb_copy_datagram_const_iovec().
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