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Message-ID: <e245fb6a37d3c99df6efa934c5f05616bc1df7e7.camel@redhat.com>
Subject: Re: [syzbot] [mptcp?] WARNING in subflow_data_ready
From:   Paolo Abeni <pabeni@redhat.com>
To:     syzbot <syzbot+c53d4d3ddb327e80bc51@syzkaller.appspotmail.com>,
        davem@davemloft.net, edumazet@google.com, kuba@kernel.org,
        linux-kernel@vger.kernel.org, martineau@kernel.org,
        matthieu.baerts@tessares.net, matttbe@kernel.org,
        mptcp@lists.linux.dev, netdev@vger.kernel.org,
        syzkaller-bugs@googlegroups.com
Date:   Fri, 27 Oct 2023 19:15:37 +0200
In-Reply-To: <0000000000000fed5606088ee598@google.com>
References: <0000000000000fed5606088ee598@google.com>
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On Wed, 2023-10-25 at 11:48 -0700, syzbot wrote:
> syzbot found the following issue on:
>=20
> HEAD commit:    9c5d00cb7b6b Merge tag 'perf-tools-fixes-for-v6.6-2-2023-=
1..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=3D123fbacd68000=
0
> kernel config:  https://syzkaller.appspot.com/x/.config?x=3D530f7d8ed0a57=
417
> dashboard link: https://syzkaller.appspot.com/bug?extid=3Dc53d4d3ddb327e8=
0bc51
> compiler:       gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for D=
ebian) 2.40

FTR: preemptible kernel, last mptcp program run on the CPU splatting
is:

r0 =3D socket$inet_mptcp(0x2, 0x1, 0x106)
bind$inet(r0, &(0x7f0000000040)=3D{0x2, 0x4e24, @multicast2}, 0x10)
sendmmsg$inet(r0, &(0x7f0000000440)=3D[{{&(0x7f00000000c0)=3D{0x2, 0x4e24, =
@empty}, 0x10, 0x0}}], 0x1, 0x24040890)
r1 =3D socket$nl_generic(0x10, 0x3, 0x10)
r2 =3D syz_genetlink_get_family_id$mptcp(&(0x7f0000000080), 0xfffffffffffff=
fff)
setsockopt$inet_tcp_buf(r0, 0x6, 0xd, &(0x7f0000000140)=3D"a7", 0x1)
sendmsg$MPTCP_PM_CMD_ADD_ADDR(r1, &(0x7f0000000300)=3D{0x0, 0x0, &(0x7f0000=
000100)=3D{&(0x7f0000000000)=3D{0x28, r2, 0x1, 0x0, 0x0, {0x2}, [@MPTCP_PM_=
ATTR_ADDR=3D{0x14, 0x1, 0x0, 0x1, [@MPTCP_PM_ADDR_ATTR_ADDR4=3D{0x8, 0x3, @=
multicast2=3D0x7f000001}, @MPTCP_PM_ADDR_ATTR_FAMILY=3D{0x6, 0x1, 0x2}]}]},=
 0x28}, 0x1, 0xf00000000000000}, 0x0)

self-connecting fast-open with an empty data buffer (on a preemptible
kernel, what could possibly go wrong?!? :-P)

The splat is caused by the following check:

	WARN_ON_ONCE(!__mptcp_check_fallback(msk) && !subflow->mp_capable &&
                     !subflow->mp_join && !(state & TCPF_CLOSE));

Without a repro it's hard to guess what is going on, but looks a valid
mptcp related issue.

/P