netdev - Re: [PATCH net] socket, bpf: fix possible use after free

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Message-ID: <20171002193506.lx6sfr3hejdzarsl@ast-mbp.dhcp.thefacebook.com>
Date:   Mon, 2 Oct 2017 12:35:08 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Eric Dumazet <eric.dumazet@...il.com>
Cc:     David Miller <davem@...emloft.net>,
        netdev <netdev@...r.kernel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>
Subject: Re: [PATCH net] socket, bpf: fix possible use after free

On Mon, Oct 02, 2017 at 12:20:51PM -0700, Eric Dumazet wrote:
> From: Eric Dumazet <edumazet@...gle.com>
> 
> Starting from linux-4.4, 3WHS no longer takes the listener lock.
> 
> Since this time, we might hit a use-after-free in sk_filter_charge(),
> if the filter we got in the memcpy() of the listener content
> just happened to be replaced by a thread changing listener BPF filter.
> 
> To fix this, we need to make sure the filter refcount is not already
> zero before incrementing it again.
> 
> Fixes: e994b2f0fb92 ("tcp: do not lock listener to process SYN packets")
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>

Thanks for the fix!
Acked-by: Alexei Starovoitov <ast@...nel.org>