Message-ID: <CAJnrk1Y1ZEsAyCv_gBCYvSdRqkzOQCC3cf8M7r8uxOHVVup-zw@mail.gmail.com>
Date:   Fri, 10 Jun 2022 11:09:44 -0700
From:   Joanne Koong <joannelkoong@...il.com>
To:     Mat Martineau <mathew.j.martineau@...ux.intel.com>
Cc:     netdev <netdev@...r.kernel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Martin KaFai Lau <kafai@...com>,
        Jakub Kicinski <kuba@...nel.org>,
        David Miller <davem@...emloft.net>,
        Paolo Abeni <pabeni@...hat.com>
Subject: Re: [PATCH net-next v2 0/2] Update bhash2 when socket's rcv saddr changes

On Thu, Jun 9, 2022 at 5:37 PM Mat Martineau
<mathew.j.martineau@...ux.intel.com> wrote:
>
> On Thu, 9 Jun 2022, Joanne Koong wrote:
>
> > On Wed, Jun 8, 2022 at 1:27 PM Joanne Koong <joannelkoong@...il.com> wrote:
> >>
> >> On Tue, Jun 7, 2022 at 10:33 AM Mat Martineau
> >> <mathew.j.martineau@...ux.intel.com> wrote:
> >>>
> >>> On Mon, 6 Jun 2022, Joanne Koong wrote:
> >>>
> >>>> On Fri, Jun 3, 2022 at 5:38 PM Joanne Koong <joannelkoong@...il.com> wrote:
> >>>>>
> >>>>> On Fri, Jun 3, 2022 at 11:55 AM Mat Martineau
> >>>>> <mathew.j.martineau@...ux.intel.com> wrote:
> >>>>>>
> >>>>>> On Thu, 2 Jun 2022, Joanne Koong wrote:
> >>>>>>
> >>>>>>> As syzbot noted [1], there is an inconsistency in the bhash2 table in the
> >>>>>>> case where a socket's rcv saddr changes after it is binded. (For more
> >>>>>>> details, please see the commit message of the first patch)
> >>>>>>>
> >>>>>>> This patchset fixes that and adds a test that triggers the case where the
> >>>>>>> sk's rcv saddr changes. The subsequent listen() call should succeed.
> >>>>>>>
> >>>>>>> [1] https://lore.kernel.org/netdev/0000000000003f33bc05dfaf44fe@google.com/
> >>>>>>>
> >>>>>>> --
> >>>>>>> v1 -> v2:
> >>>>>>> v1: https://lore.kernel.org/netdev/20220601201434.1710931-1-joannekoong@fb.com/
> >>>>>>> * Mark __inet_bhash2_update_saddr as static
> >>>>>>>
> >>>>>>> Joanne Koong (2):
> >>>>>>>  net: Update bhash2 when socket's rcv saddr changes
> >>>>>>>  selftests/net: Add sk_bind_sendto_listen test
> >>>>>>>
> >>>>>>
> >>>>>> Hi Joanne -
> >>>>>>
> >>>>>> I've been running my own syzkaller instance with v1 of this fix for a
> >>>>>> couple of days. Before this patch, syzkaller would trigger the
> >>>>>> inet_csk_get_port warning a couple of times per hour. After this patch it
> >>>>>> took two days to show the warning:
> >>>>>>
> >>>>>> ------------[ cut here ]------------
> >>>>>>
> >>>>>> WARNING: CPU: 0 PID: 9430 at net/ipv4/inet_connection_sock.c:525
> >>>>>> inet_csk_get_port+0x938/0xe80 net/ipv4/inet_connection_sock.c:525
> >>>>>> Modules linked in:
> >>>>>> CPU: 0 PID: 9430 Comm: syz-executor.5 Not tainted 5.18.0-05016-g433fde5b4119 #3
> >>>>>> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1 04/01/2014
> >>>>>> RIP: 0010:inet_csk_get_port+0x938/0xe80 net/ipv4/inet_connection_sock.c:525
> >>>>>> Code: ff 48 89 84 24 b0 00 00 00 48 85 c0 0f 84 6a 01 00 00 e8 2b 0f db fd 48 8b 6c 24 70 c6 04 24 01 e9 fb fb ff ff e8 18 0f db fd <0f> 0b e9 70 f9 ff ff e8 0c 0f db fd 0f 0b e9 28 f9 ff ff e8 00 0f
> >>>>>> RSP: 0018:ffffc90000b5fbc0 EFLAGS: 00010212
> >>>>>> RAX: 00000000000000e7 RBX: ffff88803c410040 RCX: ffffc9000e419000
> >>>>>> RDX: 0000000000040000 RSI: ffffffff836f47e8 RDI: ffff88803c4106e0
> >>>>>> RBP: ffff88810b773840 R08: 0000000000000001 R09: 0000000000000001
> >>>>>> R10: fffffbfff0f64303 R11: 0000000000000001 R12: 0000000000000000
> >>>>>> R13: ffff88810605e2f0 R14: ffffffff88606040 R15: 000000000000c1ff
> >>>>>> FS:  00007fada4d03640(0000) GS:ffff88811ac00000(0000) knlGS:0000000000000000
> >>>>>> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> >>>>>> CR2: 0000001b32e24000 CR3: 00000001016de001 CR4: 0000000000770ef0
> >>>>>> PKRU: 55555554
> >>>>>> Call Trace:
> >>>>>>   <TASK>
> >>>>>>   inet_csk_listen_start+0x143/0x3d0 net/ipv4/inet_connection_sock.c:1178
> >>>>>>   inet_listen+0x22f/0x650 net/ipv4/af_inet.c:228
> >>>>>>   mptcp_listen+0x205/0x440 net/mptcp/protocol.c:3564
> >>>>>>   __sys_listen+0x189/0x260 net/socket.c:1810
> >>>>>>   __do_sys_listen net/socket.c:1819 [inline]
> >>>>>>   __se_sys_listen net/socket.c:1817 [inline]
> >>>>>>   __x64_sys_listen+0x54/0x80 net/socket.c:1817
> >>>>>>   do_syscall_x64 arch/x86/entry/common.c:50 [inline]
> >>>>>>   do_syscall_64+0x38/0x90 arch/x86/entry/common.c:80
> >>>>>>   entry_SYSCALL_64_after_hwframe+0x46/0xb0
> >>>>>> RIP: 0033:0x7fada558f92d
> >>>>>> Code: 02 b8 ff ff ff ff c3 66 0f 1f 44 00 00 f3 0f 1e fa 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 b0 ff ff ff f7 d8 64 89 01 48
> >>>>>> RSP: 002b:00007fada4d03028 EFLAGS: 00000246 ORIG_RAX: 0000000000000032
> >>>>>> RAX: ffffffffffffffda RBX: 00007fada56aff60 RCX: 00007fada558f92d
> >>>>>> RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000004
> >>>>>> RBP: 00007fada56000a0 R08: 0000000000000000 R09: 0000000000000000
> >>>>>> R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
> >>>>>> R13: 000000000000000b R14: 00007fada56aff60 R15: 00007fada4ce3000
> >>>>>>   </TASK>
> >>>>>> irq event stamp: 2078
> >>>>>> hardirqs last  enabled at (2092): [<ffffffff812f1be3>] __up_console_sem+0xb3/0xd0 kernel/printk/printk.c:291
> >>>>>> hardirqs last disabled at (2103): [<ffffffff812f1bc8>] __up_console_sem+0x98/0xd0 kernel/printk/printk.c:289
> >>>>>> softirqs last  enabled at (1498): [<ffffffff83807dd4>] lock_sock include/net/sock.h:1691 [inline]
> >>>>>> softirqs last  enabled at (1498): [<ffffffff83807dd4>] inet_listen+0x94/0x650 net/ipv4/af_inet.c:199
> >>>>>> softirqs last disabled at (1500): [<ffffffff836f425c>] spin_lock_bh include/linux/spinlock.h:354 [inline]
> >>>>>> softirqs last disabled at (1500): [<ffffffff836f425c>] inet_csk_get_port+0x3ac/0xe80 net/ipv4/inet_connection_sock.c:483
> >>>>>> ---[ end trace 0000000000000000 ]---
> >>>>>>
> >>>>>>
> >>>>>> In the full log file it does look like syskaller is doing something
> >>>>>> strange since it's calling bind, connect, and listen on the same socket:
> >>>>>>
> >>>>>> r4 = socket$inet_mptcp(0x2, 0x1, 0x106)
> >>>>>> bind$inet(r4, &(0x7f0000000000)={0x2, 0x4e23, @empty}, 0x10)
> >>>>>> connect$inet(r4, &(0x7f0000000040)={0x2, 0x0, @local}, 0x10)
> >>>>>> listen(r4, 0x0)
> >>>>>>
> >>>>>> ...but it is a fuzz tester after all.
> >>>>>>
> >>>>>> I've uploaded the full syzkaller logs to this GitHub issue:
> >>>>>>
> >>>>>> https://github.com/multipath-tcp/mptcp_net-next/issues/279
> >>>>>>
> >>>>>>
> >>>>>> Not sure yet if this is MPTCP-related. I don't think MPTCP
> >>>>>> changes anything with the subflow TCP socket bind hashes.
> >>>>>>
> >>>>> Hi Mat,
> >>>>>
> >>>>> Thanks for bringing this up and for uploading the logs. I will look into this.
> >>>>>>
> >>>> Hi Mat,
> >>>>
> >>>> I am still trying to configure my local environment for mptcp to repro
> >>>> + test the fix to verify that it is correct. I think the fix is to add
> >>>> "inet_bhash2_update_saddr(msk);" to the end of the
> >>>> "mptcp_copy_inaddrs" function in net/mptcp/protocol.c.  Would you be
> >>>> able to run an instance on your local syzkaller environment with this
> >>>> line added to see if that fixes the warning?
> >>>
> >>> Hi Joanne -
> >>>
> >>> I also investigated that function when trying to figure out why this
> >>> warning might be happening in MPTCP.
> >>>
> >>> In MPTCP, the userspace-facing MPTCP socket (msk) doesn't directly bind or
> >>> connect. The msk creates and manages TCP subflow sockets (ssk in
> >>> mptcp_copy_inaddrs()), and passes through bind and connect calls to the
> >>> subflows. The msk depends on the subflow to do the hash updates, since
> >>> those subflow sockets are the ones interacting with the inet layer.
> >>>
> >>> mptcp_copy_inaddrs() copies the already-hashed addresses and ports from
> >>> the ssk to the msk, and we only want the ssk in the hash table.
> >>>
> >> I see, thanks for the explanation, Mat! I will keep investigating.\
> >
> > Are you able to repro this warning locally, Mat?
> >
>
> This message made it to my inbox after hitting 'send' on my last reply to
> this thread!
>
> As I said there, I haven't seen syzkaller trigger this again. It only
> happened one time after applying the fix, and not at all in the last week
> running syzkaller (nearly) continuously.
>
> > I have a test program that calls:
> > struct addrinfo hints = {
> >          .ai_protocol = IPPROTO_TCP,
> >          .ai_socktype = SOCK_STREAM,
> >         .ai_family = AF_INET,
> > };
> > getaddrinfo("127.0.0.1", "15432", &hints, &addr);
> > socket(AF_INET, SOCK_STREAM, IPPROTO_MPTCP);
> > bind(sock_fd, addr->ai_addr, addr->ai_addrlen)
> > connect(sock_fd, &zeroed_sockaddr, sizeof(zeroed_sockaddr));
> > listen(sock_fd, 0);
> >
> > but I'm unable to trigger this warning in my local environment.
> >
> > I'm not understanding how this warning can get triggered
> > non-deterministically when the socket resides only within the program.
> > The only theory that makes sense to me is that the subflow sockets'
> > saddr changes somewhere after it has been binded, but then wouldn't
> > that trigger this warning deterministically?
>
> I agree, if the MPTCP code was modifying the subflow saddr this would
> trigger more consistently. But as far as I can tell, MPTCP isn't
> changing those values.
>
> >
> > How often are you seeing this warning show up in the mptcp syzkaller?
> > Is there a way to run a local patch on the mptcp syzkaller (eg like a
> > patch that prints out extraneous debugging information about
> > icsk_bind2_hash address, tb2 address, and the socket's saddr changes)
> > - if so, how can I do this?
> >
>
> Since the warning has not repeated in the last week, I'm wondering if
> maybe the fuzz tester happened across the locking issue that Paolo noted?
> The lack of determinism makes me suspect some kind of concurrency issue.
>
> I'm running syzkaller on a large-ish datacenter VM with a kernel I
> compiled, so I can add any patches myself and run with those. Setup for
> syzkaller as I've been using it with MPTCP is documented here:
> https://github.com/multipath-tcp/mptcp_net-next/wiki/Testing#syzkaller
>
> If you have a patch with some extra debug output that you can point me to,
> I can apply that to the kernel I'm running.
>

Awesome, I'm glad to hear that the warning is not constantly
happening. I am tidying up the bhash2 locks patch and will submit that
soon. If this warning still shows up after that patch, then I will
send you a local patch with extra debug output to run on top of the
mptcp syzkaller.

Thanks!

> --
> Mat Martineau
> Intel

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