From 871019b22d1bcc9fab2d1feba1b9a564acbb6e99 Mon Sep 17 00:00:00 2001 From: Stanislav Fomichev Date: Wed, 8 Nov 2023 13:13:25 -0800 Subject: net: set SOCK_RCU_FREE before inserting socket into hashtable We've started to see the following kernel traces: WARNING: CPU: 83 PID: 0 at net/core/filter.c:6641 sk_lookup+0x1bd/0x1d0 Call Trace: __bpf_skc_lookup+0x10d/0x120 bpf_sk_lookup+0x48/0xd0 bpf_sk_lookup_tcp+0x19/0x20 bpf_prog_+0x37c/0x16a3 cls_bpf_classify+0x205/0x2e0 tcf_classify+0x92/0x160 __netif_receive_skb_core+0xe52/0xf10 __netif_receive_skb_list_core+0x96/0x2b0 napi_complete_done+0x7b5/0xb70 _poll+0x94/0xb0 net_rx_action+0x163/0x1d70 __do_softirq+0xdc/0x32e asm_call_irq_on_stack+0x12/0x20 do_softirq_own_stack+0x36/0x50 do_softirq+0x44/0x70 __inet_hash can race with lockless (rcu) readers on the other cpus: __inet_hash __sk_nulls_add_node_rcu <- (bpf triggers here) sock_set_flag(SOCK_RCU_FREE) Let's move the SOCK_RCU_FREE part up a bit, before we are inserting the socket into hashtables. Note, that the race is really harmless; the bpf callers are handling this situation (where listener socket doesn't have SOCK_RCU_FREE set) correctly, so the only annoyance is a WARN_ONCE. More details from Eric regarding SOCK_RCU_FREE timeline: Commit 3b24d854cb35 ("tcp/dccp: do not touch listener sk_refcnt under synflood") added SOCK_RCU_FREE. At that time, the precise location of sock_set_flag(sk, SOCK_RCU_FREE) did not matter, because the thread calling __inet_hash() owns a reference on sk. SOCK_RCU_FREE was only tested at dismantle time. Commit 6acc9b432e67 ("bpf: Add helper to retrieve socket in BPF") started checking SOCK_RCU_FREE _after_ the lookup to infer whether the refcount has been taken care of. Fixes: 6acc9b432e67 ("bpf: Add helper to retrieve socket in BPF") Reviewed-by: Eric Dumazet Signed-off-by: Stanislav Fomichev Reviewed-by: Kuniyuki Iwashima Signed-off-by: David S. Miller --- net/ipv4/inet_hashtables.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'net/ipv4') diff --git a/net/ipv4/inet_hashtables.c b/net/ipv4/inet_hashtables.c index 598c1b114d2c..a532f749e477 100644 --- a/net/ipv4/inet_hashtables.c +++ b/net/ipv4/inet_hashtables.c @@ -751,12 +751,12 @@ int __inet_hash(struct sock *sk, struct sock *osk) if (err) goto unlock; } + sock_set_flag(sk, SOCK_RCU_FREE); if (IS_ENABLED(CONFIG_IPV6) && sk->sk_reuseport && sk->sk_family == AF_INET6) __sk_nulls_add_node_tail_rcu(sk, &ilb2->nulls_head); else __sk_nulls_add_node_rcu(sk, &ilb2->nulls_head); - sock_set_flag(sk, SOCK_RCU_FREE); sock_prot_inuse_add(sock_net(sk), sk->sk_prot, 1); unlock: spin_unlock(&ilb2->lock); -- cgit