Re: [PATCH net-next v2 0/2] Update bhash2 when socket's rcv saddr changes

[Mat Martineau <mathew.j.martineau@linux.intel.com>]

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.


--
Mat Martineau
Intel