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From:   Martin Lau <kafai@fb.com>
To:     Lorenz Bauer <lmb@cloudflare.com>
CC:     Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        "David S. Miller" <davem@davemloft.net>,
        Joe Stringer <joe@isovalent.com>,
        "netdev@vger.kernel.org" <netdev@vger.kernel.org>,
        "bpf@vger.kernel.org" <bpf@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "kernel-team@cloudflare.com" <kernel-team@cloudflare.com>
Subject: Re: [PATCH bpf v2] net: bpf: don't leak time wait and request sockets
Thread-Topic: [PATCH bpf v2] net: bpf: don't leak time wait and request
 sockets
Thread-Index: AQHVx7l9Y1n5XH7dBkG8DtIR/ncd4KfkGrgA
Date:   Fri, 10 Jan 2020 16:43:32 +0000
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 <20200110132336.26099-1-lmb@cloudflare.com>
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On Fri, Jan 10, 2020 at 01:23:36PM +0000, Lorenz Bauer wrote:
> It's possible to leak time wait and request sockets via the following
> BPF pseudo code:
> =A0
>   sk =3D bpf_skc_lookup_tcp(...)
>   if (sk)
>     bpf_sk_release(sk)
>=20
> If sk->sk_state is TCP_NEW_SYN_RECV or TCP_TIME_WAIT the refcount taken
> by bpf_skc_lookup_tcp is not undone by bpf_sk_release. This is because
> sk_flags is re-used for other data in both kinds of sockets. The check
>=20
>   !sock_flag(sk, SOCK_RCU_FREE)
>=20
> therefore returns a bogus result. Check that sk_flags is valid by calling
> sk_fullsock. Skip checking SOCK_RCU_FREE if we already know that sk is
> not a full socket.
Acked-by: Martin KaFai Lau <kafai@fb.com>