Re: [PATCH] tcp: Do not reset the icsk_ca_initialized in tcp_init_transfer.

From: Martin KaFai Lau <kafai@fb.com>
To: Phi Nguyen <phind.uet@gmail.com>
Cc: Neal Cardwell <ncardwell@google.com>,
	Eric Dumazet <edumazet@google.com>,
	David Miller <davem@davemloft.net>,
	Hideaki YOSHIFUJI <yoshfuji@linux-ipv6.org>,
	David Ahern <dsahern@kernel.org>,
	Jakub Kicinski <kuba@kernel.org>,
	Alexei Starovoitov <ast@kernel.org>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Andrii Nakryiko <andrii@kernel.org>,
	Song Liu <songliubraving@fb.com>,
	John Fastabend <john.fastabend@gmail.com>, <kpsingh@kernel.org>,
	netdev <netdev@vger.kernel.org>,
	LKML <linux-kernel@vger.kernel.org>, bpf <bpf@vger.kernel.org>,
	<linux-kernel-mentees@lists.linuxfoundation.org>,
	<syzbot+f1e24a0594d4e3a895d3@syzkaller.appspotmail.com>,
	Yuchung Cheng <ycheng@google.com>
Subject: Re: [PATCH] tcp: Do not reset the icsk_ca_initialized in tcp_init_transfer.
Date: Mon, 28 Jun 2021 16:41:26 -0700	[thread overview]
Message-ID: <20210628234126.ijdbstfmlsycbqbp@kafai-mbp.dhcp.thefacebook.com> (raw)
In-Reply-To: <CADVnQynqMQhO4cBON=xUCkne9-E1hze3naMZZ8tQ-a0k71kh8g@mail.gmail.com>

On Mon, Jun 28, 2021 at 01:20:19PM -0400, Neal Cardwell wrote:
> )
> 
> On Mon, Jun 28, 2021 at 1:15 PM Phi Nguyen <phind.uet@gmail.com> wrote:
> >
> > On 6/29/2021 12:24 AM, Neal Cardwell wrote:
> >
> > > Thanks.
> > >
> > > Can you also please provide a summary of the event sequence that
> > > triggers the bug? Based on your Reported-by tag, I guess this is based
> > > on the syzbot reproducer:
> > >
> > >   https://groups.google.com/g/syzkaller-bugs/c/VbHoSsBz0hk/m/cOxOoTgPCAAJ 
> > >
> > > but perhaps you can give a summary of the event sequence that causes
> > > the bug? Is it that the call:
> > >
> > > setsockopt$inet_tcp_TCP_CONGESTION(r0, 0x6, 0xd,
> > > &(0x7f0000000000)='cdg\x00', 0x4)
> > >
> > > initializes the CC and happens before the connection is established,
> > > and then when the connection is established, the line that sets:
> > >    icsk->icsk_ca_initialized = 0;
> > > is incorrect, causing the CC to be initialized again without first
> > > calling the cleanup code that deallocates the CDG-allocated memory?
> > >
> > > thanks,
> > > neal
> > >
> >
> > Hi Neal,
> >
> > The gdb stack trace that lead to init_transfer_input() is as bellow, the
> > current sock state is TCP_SYN_RECV.
> 
> Thanks. That makes sense as a snapshot of time for
> tcp_init_transfer(), but I think what would be more useful would be a
> description of the sequence of events, including when the CC was
> initialized previous to that point (as noted above, was it that the
> setsockopt(TCP_CONGESTION) completed before that point?).
+1.  It needs to first explain when was the very first CC initialized.