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

In the Linux kernel, the following vulnerability has been resolved: ipv4: ip_tunnel: Fix suspicious RCU usage warning in ip_tunnel_init_flow() There are code paths from which the function is called without holding the RCU read lock, resulting in a suspicious RCU usage warning [1]. Fix by using l3mdev_master_upper_ifindex_by_index() which will acquire the RCU read lock before calling l3mdev_master_upper_ifindex_by_index_rcu(). [1] WARNING: suspicious RCU usage 6.12.0-rc3-custom-gac8f72681cf2 #141 Not tainted ----------------------------- net/core/dev.c:876 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/361: #0: ffffffff86fc7cb0 (rtnl_mutex){+.+.}-{3:3}, at: rtnetlink_rcv_msg+0x377/0xf60 stack backtrace: CPU: 3 UID: 0 PID: 361 Comm: ip Not tainted 6.12.0-rc3-custom-gac8f72681cf2 #141 Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011 Call Trace: <TASK> dump_stack_lvl+0xba/0x110 lockdep_rcu_suspicious.cold+0x4f/0xd6 dev_get_by_index_rcu+0x1d3/0x210 l3mdev_master_upper_ifindex_by_index_rcu+0x2b/0xf0 ip_tunnel_bind_dev+0x72f/0xa00 ip_tunnel_newlink+0x368/0x7a0 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