Jakub Sitnicki wrote: > On Sun, Jan 12, 2020 at 12:14 AM CET, John Fastabend wrote: > > Jakub Sitnicki wrote: > >> sk_msg and ULP frameworks override protocol callbacks pointer in > >> sk->sk_prot, while TCP accesses it locklessly when cloning the listening > >> socket. > >> > >> Once we enable use of listening sockets with sockmap (and hence sk_msg), > >> there can be shared access to sk->sk_prot if socket is getting cloned while > >> being inserted/deleted to/from the sockmap from another CPU. Mark the > >> shared access with READ_ONCE/WRITE_ONCE annotations. > >> > >> Signed-off-by: Jakub Sitnicki <jakub@xxxxxxxxxxxxxx> > > > > In sockmap side I fixed this by wrapping the access in a lock_sock[0]. So > > Do you think this is still needed with that in mind? The bpf_clone call > > is using sk_prot_creater and also setting the newsk's proto field. Even > > if the listening parent sock was being deleted in parallel would that be > > a problem? We don't touch sk_prot_creator from the tear down path. I've > > only scanned the 3..11 patches so maybe the answer is below. If that is > > the case probably an improved commit message would be helpful. > > I think it is needed. Not because of tcp_bpf_clone or that we access > listener's sk_prot_creator from there, if I'm grasping your question. > > Either way I'm glad this came up. Let's go though my reasoning and > verify it. tcp stack accesses the listener sk_prot while cloning it: > > tcp_v4_rcv > sk = __inet_lookup_skb(...) > tcp_check_req(sk) > inet_csk(sk)->icsk_af_ops->syn_recv_sock > tcp_v4_syn_recv_sock > tcp_create_openreq_child > inet_csk_clone_lock > sk_clone_lock > READ_ONCE(sk->sk_prot) > > It grabs a reference to the listener, but doesn't grab the sk_lock. > > On another CPU we can be inserting/removing the listener socket from the > sockmap and writing to its sk_prot. We have the update and the remove > path: > > sock_map_ops->map_update_elem > sock_map_update_elem > sock_map_update_common > sock_map_link_no_progs > tcp_bpf_init > tcp_bpf_update_sk_prot > sk_psock_update_proto > WRITE_ONCE(sk->sk_prot, ops) > > sock_map_ops->map_delete_elem > sock_map_delete_elem > __sock_map_delete > sock_map_unref > sk_psock_put > sk_psock_drop > sk_psock_restore_proto > tcp_update_ulp > WRITE_ONCE(sk->sk_prot, proto) > > Following the guidelines from KTSAN project [0], sk_prot looks like a > candidate for annotating it. At least on these 3 call paths. > > If that sounds correct, I can add it to the patch description. > > Thanks, > -jkbs > > [0] https://github.com/google/ktsan/wiki/READ_ONCE-and-WRITE_ONCE Hi Jakub, can push this to bpf tree as well? There is another case already in-kernel where this is needed. If the map is removed while a recvmsg is in flight. tcp_bpf_recvmsg() psock = sk_psock_get(sk) <- refcnt 2 lock_sock(sk); ... sock_map_free() <- refcnt 1 release_sock(sk) sk_psock_put() <- refcnt 0 Then can you add this diff as well I got a bit too carried away with that. If your busy I can do it as well if you want. Thanks! diff --git a/net/core/skmsg.c b/net/core/skmsg.c index 3866d7e20c07..ded2d5227678 100644 --- a/net/core/skmsg.c +++ b/net/core/skmsg.c @@ -594,8 +594,6 @@ EXPORT_SYMBOL_GPL(sk_psock_destroy); void sk_psock_drop(struct sock *sk, struct sk_psock *psock) { - sock_owned_by_me(sk); - sk_psock_cork_free(psock); sk_psock_zap_ingress(psock);
