From 38207a5e81230d6ffbdd51e5fa5681be5116dcae Mon Sep 17 00:00:00 2001 From: John Fastabend Date: Fri, 19 Nov 2021 10:14:17 -0800 Subject: bpf, sockmap: Attach map progs to psock early for feature probes When a TCP socket is added to a sock map we look at the programs attached to the map to determine what proto op hooks need to be changed. Before the patch in the 'fixes' tag there were only two categories -- the empty set of programs or a TX policy. In any case the base set handled the receive case. After the fix we have an optimized program for receive that closes a small, but possible, race on receive. This program is loaded only when the map the psock is being added to includes a RX policy. Otherwise, the race is not possible so we don't need to handle the race condition. In order for the call to sk_psock_init() to correctly evaluate the above conditions all progs need to be set in the psock before the call. However, in the current code this is not the case. We end up evaluating the requirements on the old prog state. If your psock is attached to multiple maps -- for example a tx map and rx map -- then the second update would pull in the correct maps. But, the other pattern with a single rx enabled map the correct receive hooks are not used. The result is the race fixed by the patch in the fixes tag below may still be seen in this case. To fix we simply set all psock->progs before doing the call into sock_map_init(). With this the init() call gets the full list of programs and chooses the correct proto ops on the first iteration instead of requiring the second update to pull them in. This fixes the race case when only a single map is used. Fixes: c5d2177a72a16 ("bpf, sockmap: Fix race in ingress receive verdict with redirect to self") Signed-off-by: John Fastabend Signed-off-by: Daniel Borkmann Link: https://lore.kernel.org/bpf/20211119181418.353932-2-john.fastabend@gmail.com --- net/core/sock_map.c | 10 ++++++---- 1 file changed, 6 insertions(+), 4 deletions(-) (limited to 'net') diff --git a/net/core/sock_map.c b/net/core/sock_map.c index f39ef79ced67..9b528c644fb7 100644 --- a/net/core/sock_map.c +++ b/net/core/sock_map.c @@ -282,6 +282,12 @@ static int sock_map_link(struct bpf_map *map, struct sock *sk) if (msg_parser) psock_set_prog(&psock->progs.msg_parser, msg_parser); + if (stream_parser) + psock_set_prog(&psock->progs.stream_parser, stream_parser); + if (stream_verdict) + psock_set_prog(&psock->progs.stream_verdict, stream_verdict); + if (skb_verdict) + psock_set_prog(&psock->progs.skb_verdict, skb_verdict); ret = sock_map_init_proto(sk, psock); if (ret < 0) @@ -292,14 +298,10 @@ static int sock_map_link(struct bpf_map *map, struct sock *sk) ret = sk_psock_init_strp(sk, psock); if (ret) goto out_unlock_drop; - psock_set_prog(&psock->progs.stream_verdict, stream_verdict); - psock_set_prog(&psock->progs.stream_parser, stream_parser); sk_psock_start_strp(sk, psock); } else if (!stream_parser && stream_verdict && !psock->saved_data_ready) { - psock_set_prog(&psock->progs.stream_verdict, stream_verdict); sk_psock_start_verdict(sk,psock); } else if (!stream_verdict && skb_verdict && !psock->saved_data_ready) { - psock_set_prog(&psock->progs.skb_verdict, skb_verdict); sk_psock_start_verdict(sk, psock); } write_unlock_bh(&sk->sk_callback_lock); -- cgit v1.2.3 From c0d95d3380ee099d735e08618c0d599e72f6c8b0 Mon Sep 17 00:00:00 2001 From: John Fastabend Date: Fri, 19 Nov 2021 10:14:18 -0800 Subject: bpf, sockmap: Re-evaluate proto ops when psock is removed from sockmap When a sock is added to a sock map we evaluate what proto op hooks need to be used. However, when the program is removed from the sock map we have not been evaluating if that changes the required program layout. Before the patch listed in the 'fixes' tag this was not causing failures because the base program set handles all cases. Specifically, the case with a stream parser and the case with out a stream parser are both handled. With the fix below we identified a race when running with a proto op that attempts to read skbs off both the stream parser and the skb->receive_queue. Namely, that a race existed where when the stream parser is empty checking the skb->receive_queue from recvmsg at the precies moment when the parser is paused and the receive_queue is not empty could result in skipping the stream parser. This may break a RX policy depending on the parser to run. The fix tag then loads a specific proto ops that resolved this race. But, we missed removing that proto ops recv hook when the sock is removed from the sockmap. The result is the stream parser is stopped so no more skbs will be aggregated there, but the hook and BPF program continues to be attached on the psock. User space will then get an EBUSY when trying to read the socket because the recvmsg() handler is now waiting on a stopped stream parser. To fix we rerun the proto ops init() function which will look at the new set of progs attached to the psock and rest the proto ops hook to the correct handlers. And in the above case where we remove the sock from the sock map the RX prog will no longer be listed so the proto ops is removed. Fixes: c5d2177a72a16 ("bpf, sockmap: Fix race in ingress receive verdict with redirect to self") Signed-off-by: John Fastabend Signed-off-by: Daniel Borkmann Link: https://lore.kernel.org/bpf/20211119181418.353932-3-john.fastabend@gmail.com --- net/core/skmsg.c | 5 +++++ net/core/sock_map.c | 5 ++++- 2 files changed, 9 insertions(+), 1 deletion(-) (limited to 'net') diff --git a/net/core/skmsg.c b/net/core/skmsg.c index 1ae52ac943f6..8eb671c827f9 100644 --- a/net/core/skmsg.c +++ b/net/core/skmsg.c @@ -1124,6 +1124,8 @@ void sk_psock_start_strp(struct sock *sk, struct sk_psock *psock) void sk_psock_stop_strp(struct sock *sk, struct sk_psock *psock) { + psock_set_prog(&psock->progs.stream_parser, NULL); + if (!psock->saved_data_ready) return; @@ -1212,6 +1214,9 @@ void sk_psock_start_verdict(struct sock *sk, struct sk_psock *psock) void sk_psock_stop_verdict(struct sock *sk, struct sk_psock *psock) { + psock_set_prog(&psock->progs.stream_verdict, NULL); + psock_set_prog(&psock->progs.skb_verdict, NULL); + if (!psock->saved_data_ready) return; diff --git a/net/core/sock_map.c b/net/core/sock_map.c index 9b528c644fb7..4ca4b11f4e5f 100644 --- a/net/core/sock_map.c +++ b/net/core/sock_map.c @@ -167,8 +167,11 @@ static void sock_map_del_link(struct sock *sk, write_lock_bh(&sk->sk_callback_lock); if (strp_stop) sk_psock_stop_strp(sk, psock); - else + if (verdict_stop) sk_psock_stop_verdict(sk, psock); + + if (psock->psock_update_sk_prot) + psock->psock_update_sk_prot(sk, psock, false); write_unlock_bh(&sk->sk_callback_lock); } } -- cgit v1.2.3