Re: [PATCH net] net/sched: act_bpf: use rcu_dereference_bh() to read the filter
From: Amery Hung <hidden>
Date: 2026-06-29 16:38:17
Also in:
bpf, lkml
On Mon, Jun 29, 2026 at 8:54 AM Sechang Lim [off-list ref] wrote:
tcf_bpf_act() can run from the tc egress path, which holds only
rcu_read_lock_bh(), but reads prog->filter with rcu_dereference() and
trips lockdep:
WARNING: suspicious RCU usage
net/sched/act_bpf.c:47 suspicious rcu_dereference_check() usage!
1 lock held by syz.2.1588/12756:
#0: (rcu_read_lock_bh){....}-{1:3}, at: __dev_queue_xmit net/core/dev.c:4792
tcf_bpf_act+0x6ae/0x940 net/sched/act_bpf.c:47
tcf_classify+0x6e4/0x1080 net/sched/cls_api.c:1860
sch_handle_egress net/core/dev.c:4545 [inline]
__dev_queue_xmit+0x2185/0x2c00 net/core/dev.c:4808
packet_sendmsg+0x3dfa/0x5120 net/packet/af_packet.c:3114
The other tc actions and cls_bpf already use rcu_dereference_bh() here.
Do the same.
Fixes: 1f211a1b929c ("net, sched: add clsact qdisc")
Signed-off-by: Sechang Lim <redacted>Reviewed-by: Amery Hung <redacted>
quoted hunk ↗ jump to hunk
--- net/sched/act_bpf.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)diff --git a/net/sched/act_bpf.c b/net/sched/act_bpf.c index 58a074651176..09d46e195e33 100644 --- a/net/sched/act_bpf.c +++ b/net/sched/act_bpf.c@@ -44,7 +44,7 @@ TC_INDIRECT_SCOPE int tcf_bpf_act(struct sk_buff *skb, tcf_lastuse_update(&prog->tcf_tm); bstats_update(this_cpu_ptr(prog->common.cpu_bstats), skb); - filter = rcu_dereference(prog->filter); + filter = rcu_dereference_bh(prog->filter); if (at_ingress) { __skb_push(skb, skb->mac_len); filter_res = bpf_prog_run_data_pointers(filter, skb); --2.43.0