[syzbot ci] Re: tipc: Fix use-after-free in tipc_mon_reinit_self().

[syzbot ci]

syzbot ci has tested the following series

[v1] tipc: Fix use-after-free in tipc_mon_reinit_self().
https://lore.kernel.org/all/20251106053309....@google.com
* [PATCH v1 net] tipc: Fix use-after-free in tipc_mon_reinit_self().

and found the following issue:
possible deadlock in tipc_mon_reinit_self

Full report is available here:
https://ci.syzbot.org/series/bfabf013-65e3-4ca9-8f54-0c7eef8be01a

***

possible deadlock in tipc_mon_reinit_self

tree: net
URL: https://kernel.googlesource.com/pub/scm/linux/kernel/git/netdev/net.git
base: 3d18a84eddde169d6dbf3c72cc5358b988c347d0
arch: amd64
compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
config: https://ci.syzbot.org/builds/b2774856-e331-420e-a340-5107ec4b06f9/config
C repro: https://ci.syzbot.org/findings/1f0a4298-b797-4217-8d6d-15f98c0ffd38/c_repro
syz repro: https://ci.syzbot.org/findings/1f0a4298-b797-4217-8d6d-15f98c0ffd38/syz_repro

tipc: Started in network mode
tipc: Node identity 4, cluster identity 4711
tipc: Node number set to 4
============================================
WARNING: possible recursive locking detected
syzkaller #0 Not tainted
--------------------------------------------
syz.0.17/5963 is trying to acquire lock:
ffffffff8f2cb1c8 (rtnl_mutex){+.+.}-{4:4}, at: tipc_mon_reinit_self+0x25/0x360 net/tipc/monitor.c:714

but task is already holding lock:
ffffffff8f2cb1c8 (rtnl_mutex){+.+.}-{4:4}, at: __tipc_nl_compat_doit net/tipc/netlink_compat.c:358 [inline]
ffffffff8f2cb1c8 (rtnl_mutex){+.+.}-{4:4}, at: tipc_nl_compat_doit+0x1fd/0x5f0 net/tipc/netlink_compat.c:393

other info that might help us debug this:
Possible unsafe locking scenario:

CPU0
----
lock(rtnl_mutex);
lock(rtnl_mutex);

*** DEADLOCK ***

May be due to missing lock nesting notation

3 locks held by syz.0.17/5963:
#0: ffffffff8f331050 (cb_lock){++++}-{4:4}, at: genl_rcv+0x19/0x40 net/netlink/genetlink.c:1218
#1: ffffffff8f330e68 (genl_mutex){+.+.}-{4:4}, at: genl_lock net/netlink/genetlink.c:35 [inline]
#1: ffffffff8f330e68 (genl_mutex){+.+.}-{4:4}, at: genl_op_lock net/netlink/genetlink.c:60 [inline]
#1: ffffffff8f330e68 (genl_mutex){+.+.}-{4:4}, at: genl_rcv_msg+0x10d/0x790 net/netlink/genetlink.c:1209
#2: ffffffff8f2cb1c8 (rtnl_mutex){+.+.}-{4:4}, at: __tipc_nl_compat_doit net/tipc/netlink_compat.c:358 [inline]
#2: ffffffff8f2cb1c8 (rtnl_mutex){+.+.}-{4:4}, at: tipc_nl_compat_doit+0x1fd/0x5f0 net/tipc/netlink_compat.c:393

stack backtrace:
CPU: 1 UID: 0 PID: 5963 Comm: syz.0.17 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.2-debian-1.16.2-1 04/01/2014
Call Trace:
<TASK>
dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120
print_deadlock_bug+0x28b/0x2a0 kernel/locking/lockdep.c:3041
check_deadlock kernel/locking/lockdep.c:3093 [inline]
validate_chain+0x1a3f/0x2140 kernel/locking/lockdep.c:3895
__lock_acquire+0xab9/0xd20 kernel/locking/lockdep.c:5237
lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5868
__mutex_lock_common kernel/locking/mutex.c:598 [inline]
__mutex_lock+0x187/0x1350 kernel/locking/mutex.c:760
tipc_mon_reinit_self+0x25/0x360 net/tipc/monitor.c:714
tipc_net_finalize+0x115/0x190 net/tipc/net.c:140
tipc_net_init+0x104/0x190 net/tipc/net.c:122
__tipc_nl_net_set+0x3b9/0x5a0 net/tipc/net.c:263
__tipc_nl_compat_doit net/tipc/netlink_compat.c:371 [inline]
tipc_nl_compat_doit+0x3bc/0x5f0 net/tipc/netlink_compat.c:393
tipc_nl_compat_handle net/tipc/netlink_compat.c:-1 [inline]
tipc_nl_compat_recv+0x83c/0xbe0 net/tipc/netlink_compat.c:1321
genl_family_rcv_msg_doit+0x215/0x300 net/netlink/genetlink.c:1115
genl_family_rcv_msg net/netlink/genetlink.c:1195 [inline]
genl_rcv_msg+0x60e/0x790 net/netlink/genetlink.c:1210
netlink_rcv_skb+0x208/0x470 net/netlink/af_netlink.c:2552
genl_rcv+0x28/0x40 net/netlink/genetlink.c:1219
netlink_unicast_kernel net/netlink/af_netlink.c:1320 [inline]
netlink_unicast+0x82f/0x9e0 net/netlink/af_netlink.c:1346
netlink_sendmsg+0x805/0xb30 net/netlink/af_netlink.c:1896
sock_sendmsg_nosec net/socket.c:727 [inline]
__sock_sendmsg+0x21c/0x270 net/socket.c:742
____sys_sendmsg+0x505/0x830 net/socket.c:2630
___sys_sendmsg+0x21f/0x2a0 net/socket.c:2684
__sys_sendmsg net/socket.c:2716 [inline]
__do_sys_sendmsg net/socket.c:2721 [inline]
__se_sys_sendmsg net/socket.c:2719 [inline]
__x64_sys_sendmsg+0x19b/0x260 net/socket.c:2719
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xfa/0xfa0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f13d8b8efc9
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:00007fff77cccbf8 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 00007f13d8de5fa0 RCX: 00007f13d8b8efc9
RDX: 0000000000000000 RSI: 00002000000001c0 RDI: 0000000000000003
RBP: 00007f13d8c11f91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f13d8de5fa0 R14: 00007f13d8de5fa0 R15: 0000000000000003
</TASK>


***

If these findings have caused you to resend the series or submit a
separate fix, please add the following tag to your commit message:
Tested-by: syz...@syzkaller.appspotmail.com

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