linux-kernel - Re: [PATCH v2] bpf: Fix sk_psock refcnt leak when receiving message

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Date:   Mon, 27 Apr 2020 23:21:30 +0200
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Xiyu Yang <xiyuyang19@...an.edu.cn>,
        John Fastabend <john.fastabend@...il.com>,
        Jakub Sitnicki <jakub@...udflare.com>,
        Lorenz Bauer <lmb@...udflare.com>,
        Eric Dumazet <edumazet@...gle.com>,
        "David S. Miller" <davem@...emloft.net>,
        Alexey Kuznetsov <kuznet@....inr.ac.ru>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        Jakub Kicinski <kuba@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        Andrii Nakryiko <andriin@...com>,
        KP Singh <kpsingh@...omium.org>,
        Lingpeng Chen <forrest0579@...il.com>, netdev@...r.kernel.org,
        bpf@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     yuanxzhang@...an.edu.cn, kjlu@....edu,
        Xin Tan <tanxin.ctf@...il.com>
Subject: Re: [PATCH v2] bpf: Fix sk_psock refcnt leak when receiving message

On 4/26/20 5:35 AM, Xiyu Yang wrote:
> tcp_bpf_recvmsg() invokes sk_psock_get(), which returns a reference of
> the specified sk_psock object to "psock" with increased refcnt.
> 
> When tcp_bpf_recvmsg() returns, local variable "psock" becomes invalid,
> so the refcount should be decreased to keep refcount balanced.
> 
> The reference counting issue happens in several exception handling paths
> of tcp_bpf_recvmsg(). When those error scenarios occur such as "flags"
> includes MSG_ERRQUEUE, the function forgets to decrease the refcnt
> increased by sk_psock_get(), causing a refcnt leak.
> 
> Fix this issue by calling sk_psock_put() or pulling up the error queue
> read handling when those error scenarios occur.
> 
> Fixes: e7a5f1f1cd000 ("bpf/sockmap: Read psock ingress_msg before sk_receive_queue")
> Signed-off-by: Xiyu Yang <xiyuyang19@...an.edu.cn>
> Signed-off-by: Xin Tan <tanxin.ctf@...il.com>

Applied, thanks!