xt_CHECKSUM: CHECKSUM should be avoided. If really needed, restrict with "-p udp" and only use in OUTPUT ============================= WARNING: suspicious RCU usage 5.15.185-syzkaller #0 Not tainted ----------------------------- net/sched/sch_api.c:304 suspicious rcu_dereference_protected() usage! other info that might help us debug this: rcu_scheduler_active = 2, debug_locks = 1 6 locks held by syz.8.662/7648: #0: ffff0000d53bed20 (sk_lock-AF_INET){+.+.}-{0:0}, at: lock_sock include/net/sock.h:1694 [inline] #0: ffff0000d53bed20 (sk_lock-AF_INET){+.+.}-{0:0}, at: tcp_sendmsg+0x30/0x64 net/ipv4/tcp.c:1456 #1: ffff8000143311e0 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire+0x18/0x54 include/linux/rcupdate.h:311 #2: ffff800014331240 (rcu_read_lock_bh){....}-{1:2}, at: rcu_lock_acquire+0x18/0x54 include/linux/rcupdate.h:311 #3: ffff800014331240 (rcu_read_lock_bh){....}-{1:2}, at: rcu_lock_acquire+0x18/0x54 include/linux/rcupdate.h:311 #4: ffff0000d2db8108 (&sch->q.lock){+.-.}-{2:2}, at: spin_lock include/linux/spinlock.h:363 [inline] #4: ffff0000d2db8108 (&sch->q.lock){+.-.}-{2:2}, at: __dev_xmit_skb net/core/dev.c:3911 [inline] #4: ffff0000d2db8108 (&sch->q.lock){+.-.}-{2:2}, at: __dev_queue_xmit+0x840/0x2800 net/core/dev.c:4253 #5: ffff8000143311e0 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire+0x10/0x4c include/linux/rcupdate.h:311 stack backtrace: CPU: 1 PID: 7648 Comm: syz.8.662 Not tainted 5.15.185-syzkaller #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025 Call trace: dump_backtrace+0x0/0x43c arch/arm64/kernel/stacktrace.c:152 show_stack+0x2c/0x3c arch/arm64/kernel/stacktrace.c:216 __dump_stack+0x30/0x40 lib/dump_stack.c:88 dump_stack_lvl+0xf8/0x160 lib/dump_stack.c:106 dump_stack+0x1c/0x5c lib/dump_stack.c:113 lockdep_rcu_suspicious+0x140/0x198 kernel/locking/lockdep.c:6574 qdisc_lookup+0xc8/0x64c net/sched/sch_api.c:304 qdisc_tree_reduce_backlog+0x204/0x4a0 net/sched/sch_api.c:800 cake_enqueue+0x1a3c/0x681c net/sched/sch_cake.c:1832 cbs_child_enqueue net/sched/sch_cbs.c:95 [inline] cbs_enqueue_soft+0x14c/0x230 net/sched/sch_cbs.c:128 cbs_enqueue+0x54/0x68 net/sched/sch_cbs.c:136 dev_qdisc_enqueue+0x5c/0x2fc net/core/dev.c:3852 __dev_xmit_skb net/core/dev.c:3936 [inline] __dev_queue_xmit+0xfc0/0x2800 net/core/dev.c:4253 dev_queue_xmit+0x24/0x34 net/core/dev.c:4321 neigh_hh_output include/net/neighbour.h:493 [inline] neigh_output include/net/neighbour.h:507 [inline] ip_finish_output2+0xdac/0x1228 net/ipv4/ip_output.c:228 __ip_finish_output+0x1b0/0x448 net/ipv4/ip_output.c:-1 ip_finish_output+0x40/0x218 net/ipv4/ip_output.c:316 NF_HOOK_COND include/linux/netfilter.h:291 [inline] ip_output+0x314/0x414 net/ipv4/ip_output.c:430 dst_output include/net/dst.h:452 [inline] ip_local_out net/ipv4/ip_output.c:126 [inline] __ip_queue_xmit+0xe00/0x18f0 net/ipv4/ip_output.c:532 ip_queue_xmit+0x5c/0x7c net/ipv4/ip_output.c:546 __tcp_transmit_skb+0x17ec/0x2db8 net/ipv4/tcp_output.c:1404 tcp_transmit_skb net/ipv4/tcp_output.c:1422 [inline] tcp_write_xmit+0x12e0/0x4d60 net/ipv4/tcp_output.c:2707 __tcp_push_pending_frames+0x98/0x228 net/ipv4/tcp_output.c:2892 tcp_push+0x410/0x604 net/ipv4/tcp.c:738 tcp_sendmsg_locked+0x25d0/0x2ce8 net/ipv4/tcp.c:1429 tcp_sendmsg+0x40/0x64 net/ipv4/tcp.c:1457 inet_sendmsg+0x154/0x284 net/ipv4/af_inet.c:834 sock_sendmsg_nosec net/socket.c:704 [inline] __sock_sendmsg net/socket.c:716 [inline] ____sys_sendmsg+0x61c/0x920 net/socket.c:2436 ___sys_sendmsg+0x1d0/0x240 net/socket.c:2490 __sys_sendmmsg+0x218/0x5f0 net/socket.c:2576 __do_sys_sendmmsg net/socket.c:2605 [inline] __se_sys_sendmmsg net/socket.c:2602 [inline] __arm64_sys_sendmmsg+0xa0/0xbc net/socket.c:2602 __invoke_syscall arch/arm64/kernel/syscall.c:38 [inline] invoke_syscall+0x98/0x2b8 arch/arm64/kernel/syscall.c:52 el0_svc_common+0x138/0x258 arch/arm64/kernel/syscall.c:142 do_el0_svc+0x58/0x14c arch/arm64/kernel/syscall.c:181 el0_svc+0x78/0x1e0 arch/arm64/kernel/entry-common.c:608 el0t_64_sync_handler+0xcc/0xe4 arch/arm64/kernel/entry-common.c:626 el0t_64_sync+0x1a0/0x1a4 arch/arm64/kernel/entry.S:584