netdev - Re: [PATCH] tcp: Do not reset the icsk_ca_initialized in tcp_init

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Date:   Mon, 28 Jun 2021 16:52:41 +0200
From:   Eric Dumazet <edumazet@...gle.com>
To:     Nguyen Dinh Phi <phind.uet@...il.com>
Cc:     David Miller <davem@...emloft.net>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        David Ahern <dsahern@...nel.org>,
        Jakub Kicinski <kuba@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>,
        John Fastabend <john.fastabend@...il.com>, kpsingh@...nel.org,
        netdev <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        linux-kernel-mentees@...ts.linuxfoundation.org,
        syzbot+f1e24a0594d4e3a895d3@...kaller.appspotmail.com,
        Yuchung Cheng <ycheng@...gle.com>,
        Neal Cardwell <ncardwell@...gle.com>
Subject: Re: [PATCH] tcp: Do not reset the icsk_ca_initialized in tcp_init_transfer.

On Mon, Jun 28, 2021 at 4:49 PM Nguyen Dinh Phi <phind.uet@...il.com> wrote:
>
> icsk_ca_initialized be always set to zero before we examine it in if
> block, this makes the congestion control module's initialization be
> called even if the CC module was initialized already.
> In case the CC module allocates and setups its dynamically allocated
> private data in its init() function, e.g, CDG, the memory leak may occur.
>
> Reported-by: syzbot+f1e24a0594d4e3a895d3@...kaller.appspotmail.com
>
> Signed-off-by: Nguyen Dinh Phi <phind.uet@...il.com>
> ---
>  net/ipv4/tcp_input.c | 1 -
>  1 file changed, 1 deletion(-)
>
> diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
> index 7d5e59f688de..855ada2be25e 100644
> --- a/net/ipv4/tcp_input.c
> +++ b/net/ipv4/tcp_input.c
> @@ -5922,7 +5922,6 @@ void tcp_init_transfer(struct sock *sk, int bpf_op, struct sk_buff *skb)
>                 tp->snd_cwnd = tcp_init_cwnd(tp, __sk_dst_get(sk));
>         tp->snd_cwnd_stamp = tcp_jiffies32;
>
> -       icsk->icsk_ca_initialized = 0;

Unfortunately this patch might break things.

We keep changing this CC switching, with eBPF being mixed in the equation.

I would suggest you find a Fixes: tag first, so that we can continue
the discussion.

Thank you.

>         bpf_skops_established(sk, bpf_op, skb);
>         if (!icsk->icsk_ca_initialized)
>                 tcp_init_congestion_control(sk);
> --
> 2.25.1
>