Re: [PATCH mptcp-net v2 1/3] mptcp: pm: only set fullmesh for subflow endp

[Matthieu Baerts <matttbe@kernel.org>]

Hi Mat,

On 21/01/2025 23:59, Mat Martineau wrote:
> On Fri, 17 Jan 2025, Matthieu Baerts (NGI0) wrote:
> 
>> With the in-kernel path-manager, it is possible to change the 'fullmesh'
>> flag. The code in mptcp_pm_nl_fullmesh() expects to change it only on
>> 'subflow' endpoints, to recreate more or less subflows using the linked
>> address.
>>
>> Unfortunately, the set_flags() hook was a bit more permissive, and
>> allowed 'implicit' endpoints to get the 'fullmesh' flag while it is not
>> allowed before.
>>
>> That's what syzbot found, triggering the following warning:
>>
>>  WARNING: CPU: 0 PID: 6499 at net/mptcp/pm_netlink.c:1496
>> __mark_subflow_endp_available net/mptcp/pm_netlink.c:1496 [inline]
>>  WARNING: CPU: 0 PID: 6499 at net/mptcp/pm_netlink.c:1496
>> mptcp_pm_nl_fullmesh net/mptcp/pm_netlink.c:1980 [inline]
>>  WARNING: CPU: 0 PID: 6499 at net/mptcp/pm_netlink.c:1496
>> mptcp_nl_set_flags net/mptcp/pm_netlink.c:2003 [inline]
>>  WARNING: CPU: 0 PID: 6499 at net/mptcp/pm_netlink.c:1496
>> mptcp_pm_nl_set_flags+0x974/0xdc0 net/mptcp/pm_netlink.c:2064
>>  Modules linked in:
>>  CPU: 0 UID: 0 PID: 6499 Comm: syz.1.413 Not tainted 6.13.0-rc5-
>> syzkaller-00172-gd1bf27c4e176 #0
>>  Hardware name: Google Compute Engine/Google Compute Engine, BIOS
>> Google 09/13/2024
>>  RIP: 0010:__mark_subflow_endp_available net/mptcp/pm_netlink.c:1496
>> [inline]
>>  RIP: 0010:mptcp_pm_nl_fullmesh net/mptcp/pm_netlink.c:1980 [inline]
>>  RIP: 0010:mptcp_nl_set_flags net/mptcp/pm_netlink.c:2003 [inline]
>>  RIP: 0010:mptcp_pm_nl_set_flags+0x974/0xdc0 net/mptcp/pm_netlink.c:2064
>>  Code: 01 00 00 49 89 c5 e8 fb 45 e8 f5 e9 b8 fc ff ff e8 f1 45 e8 f5
>> 4c 89 f7 be 03 00 00 00 e8 44 1d 0b f9 eb a0 e8 dd 45 e8 f5 90 <0f> 0b
>> 90 e9 17 ff ff ff 89 d9 80 e1 07 38 c1 0f 8c c9 fc ff ff 48
>>  RSP: 0018:ffffc9000d307240 EFLAGS: 00010293
>>  RAX: ffffffff8bb72e03 RBX: 0000000000000000 RCX: ffff88807da88000
>>  RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
>>  RBP: ffffc9000d307430 R08: ffffffff8bb72cf0 R09: 1ffff1100b842a5e
>>  R10: dffffc0000000000 R11: ffffed100b842a5f R12: ffff88801e2e5ac0
>>  R13: ffff88805c214800 R14: ffff88805c2152e8 R15: 1ffff1100b842a5d
>>  FS:  00005555619f6500(0000) GS:ffff8880b8600000(0000)
>> knlGS:0000000000000000
>>  CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>>  CR2: 0000000020002840 CR3: 00000000247e6000 CR4: 00000000003526f0
>>  DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
>>  DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
>>  Call Trace:
>>   <TASK>
>>   genl_family_rcv_msg_doit net/netlink/genetlink.c:1115 [inline]
>>   genl_family_rcv_msg net/netlink/genetlink.c:1195 [inline]
>>   genl_rcv_msg+0xb14/0xec0 net/netlink/genetlink.c:1210
>>   netlink_rcv_skb+0x1e3/0x430 net/netlink/af_netlink.c:2542
>>   genl_rcv+0x28/0x40 net/netlink/genetlink.c:1219
>>   netlink_unicast_kernel net/netlink/af_netlink.c:1321 [inline]
>>   netlink_unicast+0x7f6/0x990 net/netlink/af_netlink.c:1347
>>   netlink_sendmsg+0x8e4/0xcb0 net/netlink/af_netlink.c:1891
>>   sock_sendmsg_nosec net/socket.c:711 [inline]
>>   __sock_sendmsg+0x221/0x270 net/socket.c:726
>>   ____sys_sendmsg+0x52a/0x7e0 net/socket.c:2583
>>   ___sys_sendmsg net/socket.c:2637 [inline]
>>   __sys_sendmsg+0x269/0x350 net/socket.c:2669
>>   do_syscall_x64 arch/x86/entry/common.c:52 [inline]
>>   do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
>>   entry_SYSCALL_64_after_hwframe+0x77/0x7f
>>  RIP: 0033:0x7f5fe8785d29
>>  Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 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 a8 ff ff ff f7 d8 64 89 01 48
>>  RSP: 002b:00007fff571f5558 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
>>  RAX: ffffffffffffffda RBX: 00007f5fe8975fa0 RCX: 00007f5fe8785d29
>>  RDX: 0000000000000000 RSI: 0000000020000480 RDI: 0000000000000007
>>  RBP: 00007f5fe8801b08 R08: 0000000000000000 R09: 0000000000000000
>>  R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
>>  R13: 00007f5fe8975fa0 R14: 00007f5fe8975fa0 R15: 00000000000011f4
>>   </TASK>
>>
>> Here, syzbot managed to set the 'fullmesh' flag on an 'implicit' and
>> used -- according to 'id_avail_bitmap' -- endpoint, causing the PM to
>> try decrement the local_addr_used counter which is only incremented for
>> the 'subflow' endpoint.
>>
>> Note that 'no type' endpoints -- not 'subflow', 'signal', 'implicit' --
>> are fine, because their ID will not be marked as used in the 'id_avail'
>> bitmap, and setting 'fullmesh' can help forcing the creation of subflow
>> when receiving an ADD_ADDR.
>>
>> Fixes: 73c762c1f07d ("mptcp: set fullmesh flag in pm_netlink")
>> Reported-by: syzbot+cd16e79c1e45f3fe0377@syzkaller.appspotmail.com
>> Closes: https://
>> lore.kernel.org/6786ac51.050a0220.216c54.00a6.GAE@google.com
>> Closes: https://github.com/multipath-tcp/mptcp_net-next/issues/540
>> Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
>> ---
>> Notes:
>> - v2: check the two flags in one instruction. (Paolo)
> 
> v2 LGTM:
> 
> Reviewed-by: Mat Martineau <martineau@kernel.org>

Thank you for the review!

Now in our tree (fixes for -net):

New patches for t/upstream-net and t/upstream:
- c3a63555780b: mptcp: pm: only set fullmesh for subflow endp
- Results: e7c5c5982f54..28c8f5a4574b (export-net)
- 6cce766067be: conflict in t/mptcp-add-local-parameter-for-set_flags
- Results: a9a670c7f9f9..8c4d55afa2c3 (export)

Tests are now in progress:

- export-net:
https://github.com/multipath-tcp/mptcp_net-next/commit/cd6d39abeeb0ad570a1f34adef4731098cec9cb0/checks
- export:
https://github.com/multipath-tcp/mptcp_net-next/commit/3a8173007814d102c6043c8f4830f6621e87d435/checks

Cheers,
Matt
-- 
Sponsored by the NGI0 Core fund.