netdev - Re: [PATCH net] net: correct udp zerocopy refcnt also when zerocopy only on append

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Message-Id: <20190611.114408.1066206492769692313.davem@davemloft.net>
Date:   Tue, 11 Jun 2019 11:44:08 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     willemdebruijn.kernel@...il.com
Cc:     netdev@...r.kernel.org, willemb@...gle.com,
        syzkaller@...glegroups.com
Subject: Re: [PATCH net] net: correct udp zerocopy refcnt also when
 zerocopy only on append

From: Willem de Bruijn <willemdebruijn.kernel@...il.com>
Date: Fri,  7 Jun 2019 17:57:48 -0400

> From: Willem de Bruijn <willemb@...gle.com>
> 
> The below patch fixes an incorrect zerocopy refcnt increment when
> appending with MSG_MORE to an existing zerocopy udp skb.
> 
>   send(.., MSG_ZEROCOPY | MSG_MORE);	// refcnt 1
>   send(.., MSG_ZEROCOPY | MSG_MORE);	// refcnt still 1 (bar frags)
> 
> But it missed that zerocopy need not be passed at the first send. The
> right test whether the uarg is newly allocated and thus has extra
> refcnt 1 is not !skb, but !skb_zcopy.
> 
>   send(.., MSG_MORE);			// <no uarg>
>   send(.., MSG_ZEROCOPY);		// refcnt 1
> 
> Fixes: 100f6d8e09905 ("net: correct zerocopy refcnt with udp MSG_MORE")
> Reported-by: syzbot <syzkaller@...glegroups.com>
> Signed-off-by: Willem de Bruijn <willemb@...gle.com>

Applied, thanks Willem.