netdev - Re: [PATCH net] geneve: avoid use-after-free of skb->data

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Date:   Fri, 02 Dec 2016 14:09:25 -0500 (EST)
From:   David Miller <davem@...emloft.net>
To:     sd@...asysnail.net
Cc:     netdev@...r.kernel.org, linville@...driver.com
Subject: Re: [PATCH net] geneve: avoid use-after-free of skb->data

From: Sabrina Dubroca <sd@...asysnail.net>
Date: Fri,  2 Dec 2016 16:49:29 +0100

> geneve{,6}_build_skb can end up doing a pskb_expand_head(), which
> makes the ip_hdr(skb) reference we stashed earlier stale. Since it's
> only needed as an argument to ip_tunnel_ecn_encap(), move this
> directly in the function call.
> 
> Fixes: 08399efc6319 ("geneve: ensure ECN info is handled properly in all tx/rx paths")
> Signed-off-by: Sabrina Dubroca <sd@...asysnail.net>

Applied and queued up for -stable, thanks.

This bug happens so many times that I think it might be time for
a debugging mode for pskb_expand_head() that unconditionally
reallocates the skb->data buffer regardless of whether it's
necessary or not and somehow unmaps the previous buffer to
force a trap on stale pointers.

Better ideas welcome, of course :)