netdev - Re: [PATCH net,stable 1/2] l2tp: Fix PPP header erasure and memory leak

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Message-ID: <1371048080.3252.61.camel@edumazet-glaptop>
Date:	Wed, 12 Jun 2013 07:41:20 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Guillaume Nault <g.nault@...halink.fr>
Cc:	netdev@...r.kernel.org, James Chapman <jchapman@...alix.com>,
	David Miller <davem@...emloft.net>
Subject: Re: [PATCH net,stable 1/2] l2tp: Fix PPP header erasure and memory
 leak

On Wed, 2013-06-12 at 16:07 +0200, Guillaume Nault wrote:
> Copy user data after PPP framing header. This prevents erasure of the
> added PPP header and avoids leaking two bytes of uninitialised memory
> at the end of skb's data buffer.
> 
> Signed-off-by: Guillaume Nault <g.nault@...halink.fr>
> ---
>  net/l2tp/l2tp_ppp.c |    4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/net/l2tp/l2tp_ppp.c b/net/l2tp/l2tp_ppp.c
> index 637a341..681c626 100644
> --- a/net/l2tp/l2tp_ppp.c
> +++ b/net/l2tp/l2tp_ppp.c
> @@ -346,12 +346,12 @@ static int pppol2tp_sendmsg(struct kiocb *iocb, struct socket *sock, struct msgh
>  	skb_put(skb, 2);
>  
>  	/* Copy user data into skb */
> -	error = memcpy_fromiovec(skb->data, m->msg_iov, total_len);
> +	error = memcpy_fromiovec(skb_put(skb, total_len), m->msg_iov,
> +				 total_len);
>  	if (error < 0) {
>  		kfree_skb(skb);
>  		goto error_put_sess_tun;
>  	}
> -	skb_put(skb, total_len);
>  
>  	l2tp_xmit_skb(session, skb, session->hdr_len);
>  

I see no real change in your patch.

skb_put(skb, X) returns skb->data before the put operation.

Could you elaborate ?



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