ipv4: ip_tunnel: Fix suspicious RCU usage warning in ip_tunnel_find()

In the Linux kernel, the following vulnerability has been resolved:

ipv4: ip_tunnel: Fix suspicious RCU usage warning in ip_tunnel_find()

The per-netns IP tunnel hash table is protected by the RTNL mutex and

ip_tunnel_find() is only called from the control path where the mutex is

taken.

Add a lockdep expression to hlist_for_each_entry_rcu() in

ip_tunnel_find() in order to validate that the mutex is held and to

silence the suspicious RCU usage warning [1].

[1]

WARNING: suspicious RCU usage

6.12.0-rc3-custom-gd95d9a31aceb #139 Not tainted

-----------------------------

net/ipv4/ip_tunnel.c:221 RCU-list traversed in non-reader section!!

other info that might help us debug this:

rcu_scheduler_active = 2, debug_locks = 1

1 lock held by ip/362:

#0: ffffffff86fc7cb0 (rtnl_mutex){+.+.}-{3:3}, at: rtnetlink_rcv_msg+0x377/0xf60

stack backtrace:

CPU: 12 UID: 0 PID: 362 Comm: ip Not tainted 6.12.0-rc3-custom-gd95d9a31aceb #139

Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011

Call Trace:

<TASK>

dump_stack_lvl+0xba/0x110

lockdep_rcu_suspicious.cold+0x4f/0xd6

ip_tunnel_find+0x435/0x4d0

ip_tunnel_newlink+0x517/0x7a0

ipgre_newlink+0x14c/0x170

__rtnl_newlink+0x1173/0x19c0

rtnl_newlink+0x6c/0xa0

rtnetlink_rcv_msg+0x3cc/0xf60

netlink_rcv_skb+0x171/0x450

netlink_unicast+0x539/0x7f0

netlink_sendmsg+0x8c1/0xd80

____sys_sendmsg+0x8f9/0xc20

___sys_sendmsg+0x197/0x1e0

__sys_sendmsg+0x122/0x1f0

do_syscall_64+0xbb/0x1d0

entry_SYSCALL_64_after_hwframe+0x77/0x7f