netdev - Re: [bpf PATCH 2/9] bpf: sockmap, ensure sock lock held during tear down

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Date:   Thu, 9 Jan 2020 09:10:25 -0800
From:   Song Liu <song@...nel.org>
To:     John Fastabend <john.fastabend@...il.com>
Cc:     bpf <bpf@...r.kernel.org>, Networking <netdev@...r.kernel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>
Subject: Re: [bpf PATCH 2/9] bpf: sockmap, ensure sock lock held during tear down

On Wed, Jan 8, 2020 at 1:14 PM John Fastabend <john.fastabend@...il.com> wrote:
>
> The sock_map_free() and sock_hash_free() paths used to delete sockmap
> and sockhash maps walk the maps and destroy psock and bpf state associated
> with the socks in the map. When done the socks no longer have BPF programs
> attached and will function normally. This can happen while the socks in
> the map are still "live" meaning data may be sent/received during the walk.
>
> Currently, though we don't take the sock_lock when the psock and bpf state
> is removed through this path. Specifically, this means we can be writing
> into the ops structure pointers such as sendmsg, sendpage, recvmsg, etc.
> while they are also being called from the networking side. This is not
> safe, we never used proper READ_ONCE/WRITE_ONCE semantics here if we
> believed it was safe. Further its not clear to me its even a good idea
> to try and do this on "live" sockets while networking side might also
> be using the socket. Instead of trying to reason about using the socks
> from both sides lets realize that every use case I'm aware of rarely
> deletes maps, in fact kubernetes/Cilium case builds map at init and
> never tears it down except on errors. So lets do the simple fix and
> grab sock lock.
>
> This patch wraps sock deletes from maps in sock lock and adds some
> annotations so we catch any other cases easier.
>
> Fixes: 604326b41a6fb ("bpf, sockmap: convert to generic sk_msg interface")
> Signed-off-by: John Fastabend <john.fastabend@...il.com>

Acked-by: Song Liu <songliubraving@...com>