5.4-stable review patch. If anyone has any objections, please let me know.
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From: Stanislav Fomichev sdf@google.com
commit 871019b22d1bcc9fab2d1feba1b9a564acbb6e99 upstream.
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: <IRQ> __bpf_skc_lookup+0x10d/0x120 bpf_sk_lookup+0x48/0xd0 bpf_sk_lookup_tcp+0x19/0x20 bpf_prog_<redacted>+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 <redacted>_poll+0x94/0xb0 net_rx_action+0x163/0x1d70 __do_softirq+0xdc/0x32e asm_call_irq_on_stack+0x12/0x20 </IRQ> 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 edumazet@google.com Signed-off-by: Stanislav Fomichev sdf@google.com Reviewed-by: Kuniyuki Iwashima kuniyu@amazon.com Signed-off-by: David S. Miller davem@davemloft.net [Resolved conflict for 5.10 and below.] Signed-off-by: Siddh Raman Pant siddh.raman.pant@oracle.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- net/ipv4/inet_hashtables.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
--- a/net/ipv4/inet_hashtables.c +++ b/net/ipv4/inet_hashtables.c @@ -609,6 +609,7 @@ int __inet_hash(struct sock *sk, struct 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, &ilb->nulls_head); @@ -616,7 +617,6 @@ int __inet_hash(struct sock *sk, struct __sk_nulls_add_node_rcu(sk, &ilb->nulls_head); inet_hash2(hashinfo, sk); ilb->count++; - sock_set_flag(sk, SOCK_RCU_FREE); sock_prot_inuse_add(sock_net(sk), sk->sk_prot, 1); unlock: spin_unlock(&ilb->lock);