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

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Date:   Mon, 28 Jun 2021 13:09:43 -0400
From:   Neal Cardwell <ncardwell@...gle.com>
To:     Nguyen Dinh Phi <phind.uet@...il.com>
Cc:     edumazet@...gle.com, davem@...emloft.net, yoshfuji@...ux-ipv6.org,
        dsahern@...nel.org, kuba@...nel.org, ast@...nel.org,
        daniel@...earbox.net, andrii@...nel.org, kafai@...com,
        songliubraving@...com, john.fastabend@...il.com,
        kpsingh@...nel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, bpf@...r.kernel.org,
        linux-kernel-mentees@...ts.linuxfoundation.org,
        syzbot+f1e24a0594d4e3a895d3@...kaller.appspotmail.com,
        Yuchung Cheng <ycheng@...gle.com>, Kevin Yang <yyd@...gle.com>
Subject: Re: [PATCH] tcp: Do not reset the icsk_ca_initialized in tcp_init_transfer.

On Mon, Jun 28, 2021 at 11:39 AM 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;

If this patch removes that line, then AFAICT the patch should also
insert a corresponding:

  icsk->icsk_ca_initialized = 0;

in tcp_ca_openreq_child(), so that any non-zero icsk_ca_initialized
value in a listener socket (on which setsockopt(TCP_CONGESTION) was
called)  is not erroneously inherited by a child socket due to the
tcp_create_openreq_child() -> inet_csk_clone_lock() -> sock_copy()
call chain. Something like:

diff --git a/net/ipv4/tcp_minisocks.c b/net/ipv4/tcp_minisocks.c
index c48d8336f26d..4d6a76dfa1c4 100644
--- a/net/ipv4/tcp_minisocks.c
+++ b/net/ipv4/tcp_minisocks.c
@@ -446,6 +446,7 @@ void tcp_ca_openreq_child(struct sock *sk, const
struct dst_entry *dst)
        }

        /* If no valid choice made yet, assign current system default ca. */
+       icsk->icsk_ca_initialized = 0;
        if (!ca_got_dst &&
            (!icsk->icsk_ca_setsockopt ||
             !bpf_try_module_get(icsk->icsk_ca_ops, icsk->icsk_ca_ops->owner)))

thanks,
neal