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:

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

References

• https://nvd.nist.gov/vuln/detail/CVE-2024-53042
• https://git.kernel.org/stable/c/5edcb3fdb12c3d46a6e79eeeec27d925b80fc168
• https://git.kernel.org/stable/c/699b48fc31727792edf2cab3829586ae6ba649e2
• https://git.kernel.org/stable/c/6dfaa458fe923211c766238a224e0a3c0522935c
• https://git.kernel.org/stable/c/72c0f482e39c87317ebf67661e28c8d86c93e870
• https://git.kernel.org/stable/c/ad4a3ca6a8e886f6491910a3ae5d53595e40597d
• https://git.kernel.org/stable/c/e2742758c9c85c84e077ede5f916479f724e11c2