[PATCH net-next v1] flow_offload: fix suspicious RCU usage when offloading tc action

[Baowen Zheng <baowen.zheng@corigine.com>]

Fix suspicious rcu_dereference_protected() usage when offloading tc action.

We should hold tcfa_lock to offload tc action in action initiation.

Without these changes, the following warning will be observed:

WARNING: suspicious RCU usage
5.16.0-rc5-net-next-01504-g7d1f236dcffa-dirty #50 Tainted: G          I
-----------------------------
include/net/tc_act/tc_tunnel_key.h:33 suspicious rcu_dereference_protected() usage!
1 lock held by tc/12108:
CPU: 4 PID: 12108 Comm: tc Tainted: G
Hardware name: Dell Inc. PowerEdge R740/07WCGN, BIOS 1.6.11 11/20/2018
Call Trace:
<TASK>
dump_stack_lvl+0x49/0x5e
dump_stack+0x10/0x12
lockdep_rcu_suspicious+0xed/0xf8
tcf_tunnel_key_offload_act_setup+0x1de/0x300 [act_tunnel_key]
tcf_action_offload_add_ex+0xc0/0x1f0
tcf_action_init+0x26a/0x2f0
tcf_action_add+0xa9/0x1f0
tc_ctl_action+0xfb/0x170
rtnetlink_rcv_msg+0x169/0x510
? sched_clock+0x9/0x10
? rtnl_newlink+0x70/0x70
netlink_rcv_skb+0x55/0x100
rtnetlink_rcv+0x15/0x20
netlink_unicast+0x1a8/0x270
netlink_sendmsg+0x245/0x490
sock_sendmsg+0x65/0x70
____sys_sendmsg+0x219/0x260
? __import_iovec+0x2c/0x150
___sys_sendmsg+0xb7/0x100
? __lock_acquire+0x3d5/0x1f40
? __this_cpu_preempt_check+0x13/0x20
? lock_is_held_type+0xe4/0x140
? sched_clock+0x9/0x10
? ktime_get_coarse_real_ts64+0xbe/0xd0
? __this_cpu_preempt_check+0x13/0x20
? lockdep_hardirqs_on+0x7e/0x100
? ktime_get_coarse_real_ts64+0xbe/0xd0
? trace_hardirqs_on+0x2a/0xf0
__sys_sendmsg+0x5a/0xa0
? syscall_trace_enter.constprop.0+0x1dd/0x220
__x64_sys_sendmsg+0x1f/0x30
do_syscall_64+0x3b/0x90
entry_SYSCALL_64_after_hwframe+0x44/0xae
RIP: 0033:0x7f4db7bb7a60

Fixes: 8cbfe939abe9 ("flow_offload: allow user to offload tc action to net device")
Reported-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: Baowen Zheng <baowen.zheng@corigine.com>
Signed-off-by: Louis Peens <louis.peens@corigine.com>
---
 net/sched/act_api.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/net/sched/act_api.c b/net/sched/act_api.c
index b2f8a39..32563ce 100644
--- a/net/sched/act_api.c
+++ b/net/sched/act_api.c
@@ -186,12 +186,19 @@ static int offload_action_init(struct flow_offload_action *fl_action,
 			       enum offload_act_command  cmd,
 			       struct netlink_ext_ack *extack)
 {
+	int err;
+
 	fl_action->extack = extack;
 	fl_action->command = cmd;
 	fl_action->index = act->tcfa_index;
 
-	if (act->ops->offload_act_setup)
-		return act->ops->offload_act_setup(act, fl_action, NULL, false);
+	if (act->ops->offload_act_setup) {
+		spin_lock_bh(&act->tcfa_lock);
+		err = act->ops->offload_act_setup(act, fl_action, NULL,
+						  false);
+		spin_unlock_bh(&act->tcfa_lock);
+		return err;
+	}
 
 	return -EOPNOTSUPP;
 }
-- 
1.8.3.1