netdev - Re: [PATCH v2 bpf 2/2] bpf: net: Avoid incorrect bpf_sk_reuseport

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Message-ID: <20200709105833.GA1761@katalix.com>
Date:   Thu, 9 Jul 2020 11:58:33 +0100
From:   James Chapman <jchapman@...alix.com>
To:     Martin KaFai Lau <kafai@...com>
Cc:     bpf@...r.kernel.org, Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>, kernel-team@...com,
        netdev@...r.kernel.org
Subject: Re: [PATCH v2 bpf 2/2] bpf: net: Avoid incorrect
 bpf_sk_reuseport_detach call

On  Wed, Jul 08, 2020 at 23:11:10 -0700, Martin KaFai Lau wrote:
> bpf_sk_reuseport_detach is currently called when sk->sk_user_data
> is not NULL.  It is incorrect because sk->sk_user_data may not be
> managed by the bpf's reuseport_array.  It has been reported in [1] that,
> the bpf_sk_reuseport_detach() which is called from udp_lib_unhash() has
> corrupted the sk_user_data managed by l2tp.
> 
> This patch solves it by using another bit (defined as SK_USER_DATA_BPF)
> of the sk_user_data pointer value.  It marks that a sk_user_data is
> managed/owned by BPF.

I have reservations about using a bit in sk_user_data to indicate
ownership of that pointer. But putting that aside, I confirm that the
patch fixes the problem.

Acked-by: James Chapman <jchapman@...alix.com>
Tested-by: James Chapman <jchapman@...alix.com>
Reported-by: syzbot+9f092552ba9a5efca5df@...kaller.appspotmail.com