netdev - Re: [PATCH net] tcp: ensure skb->dev is NULL before leaving TCP stack

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Date:   Thu, 19 Mar 2020 21:36:57 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     edumazet@...gle.com
Cc:     netdev@...r.kernel.org, eric.dumazet@...il.com, micron10@...il.com,
        fw@...len.de, pablo@...filter.org
Subject: Re: [PATCH net] tcp: ensure skb->dev is NULL before leaving TCP
 stack

From: Eric Dumazet <edumazet@...gle.com>
Date: Thu, 19 Mar 2020 12:49:55 -0700

> skb->rbnode is sharing three skb fields : next, prev, dev
> 
> When a packet is sent, TCP keeps the original skb (master)
> in a rtx queue, which was converted to rbtree a while back.
> 
> __tcp_transmit_skb() is responsible to clone the master skb,
> and add the TCP header to the clone before sending it
> to network layer.
> 
> skb_clone() already clears skb->next and skb->prev, but copies
> the master oskb->dev into the clone.
> 
> We need to clear skb->dev, otherwise lower layers could interpret
> the value as a pointer to a netdev.
> 
> This old bug surfaced recently when commit 28f8bfd1ac94
> ("netfilter: Support iif matches in POSTROUTING") was merged.
> 
> Before this netfilter commit, skb->dev value was ignored and
> changed before reaching dev_queue_xmit()
> 
> Fixes: 75c119afe14f ("tcp: implement rb-tree based retransmit queue")
> Fixes: 28f8bfd1ac94 ("netfilter: Support iif matches in POSTROUTING")
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Reported-by: Martin Zaharinov <micron10@...il.com>

Applied and queued up for -stable, thanks Eric.