From: Daniel Borkmann <daniel@iogearbox.net>
To: Lorenz Bauer <lmb@cloudflare.com>,
John Fastabend <john.fastabend@gmail.com>,
"David S. Miller" <davem@davemloft.net>,
Jakub Kicinski <kuba@kernel.org>,
Alexei Starovoitov <ast@kernel.org>,
Martin KaFai Lau <kafai@fb.com>, Song Liu <songliubraving@fb.com>,
Yonghong Song <yhs@fb.com>, Andrii Nakryiko <andriin@fb.com>
Cc: kernel-team@cloudflare.com, netdev@vger.kernel.org,
bpf@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH bpf] bpf: sockmap: check update requirements after locking
Date: Fri, 7 Feb 2020 22:50:06 +0100 [thread overview]
Message-ID: <287e09b1-e510-4891-8d38-3a85e7a2efd4@iogearbox.net> (raw)
In-Reply-To: <20200207103713.28175-1-lmb@cloudflare.com>
On 2/7/20 11:37 AM, Lorenz Bauer wrote:
> It's currently possible to insert sockets in unexpected states into
> a sockmap, due to a TOCTTOU when updating the map from a syscall.
> sock_map_update_elem checks that sk->sk_state == TCP_ESTABLISHED,
> locks the socket and then calls sock_map_update_common. At this
> point, the socket may have transitioned into another state, and
> the earlier assumptions don't hold anymore. Crucially, it's
> conceivable (though very unlikely) that a socket has become unhashed.
> This breaks the sockmap's assumption that it will get a callback
> via sk->sk_prot->unhash.
>
> Fix this by checking the (fixed) sk_type and sk_protocol without the
> lock, followed by a locked check of sk_state.
>
> Unfortunately it's not possible to push the check down into
> sock_(map|hash)_update_common, since BPF_SOCK_OPS_PASSIVE_ESTABLISHED_CB
> run before the socket has transitioned from TCP_SYN_RECV into
> TCP_ESTABLISHED.
>
> Signed-off-by: Lorenz Bauer <lmb@cloudflare.com>
> Fixes: 604326b41a6f ("bpf, sockmap: convert to generic sk_msg interface")
Applied, thanks!
prev parent reply other threads:[~2020-02-07 21:50 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-07 10:37 [PATCH bpf] bpf: sockmap: check update requirements after locking Lorenz Bauer
2020-02-07 10:56 ` Jakub Sitnicki
2020-02-07 21:50 ` Daniel Borkmann [this message]
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