5.4-stable review patch. If anyone has any objections, please let me know.
------------------
From: Stanislav Fomichev <sdf@xxxxxxxxxx>
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@xxxxxxxxxx>
Signed-off-by: Stanislav Fomichev <sdf@xxxxxxxxxx>
Reviewed-by: Kuniyuki Iwashima <kuniyu@xxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
[Resolved conflict for 5.10 and below.]
Signed-off-by: Siddh Raman Pant <siddh.raman.pant@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
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);
