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skmsg: Improve udp_bpf_recvmsg() accuracy

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I tried to reuse sk_msg_wait_data() for different protocols,
but it turns out it can not be simply reused. For example,
UDP actually uses two queues to receive skb:
udp_sk(sk)->reader_queue and sk->sk_receive_queue. So we have
to check both of them to know whether we have received any
packet.

Also, UDP does not lock the sock during BH Rx path, it makes
no sense for its ->recvmsg() to lock the sock. It is always
possible for ->recvmsg() to be called before packets actually
arrive in the receive queue, we just use best effort to make
it accurate here.

Fixes: 1f5be6b3b0 ("udp: Implement udp_bpf_recvmsg() for sockmap")
Signed-off-by: Cong Wang <cong.wang@bytedance.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: John Fastabend <john.fastabend@gmail.com>
Acked-by: Jakub Sitnicki <jakub@cloudflare.com>
Link: https://lore.kernel.org/bpf/20210615021342.7416-2-xiyou.wangcong@gmail.com
This commit is contained in:
Cong Wang
2021-06-14 19:13:35 -07:00
committed by Daniel Borkmann
parent 61e8aeda93
commit 9f2470fbc4
4 changed files with 65 additions and 31 deletions
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2
include/linux/skmsg.h
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@@ -126,8 +126,6 @@ int sk_msg_zerocopy_from_iter(struct sock *sk, struct iov_iter *from,
struct sk_msg *msg, u32 bytes);
int sk_msg_memcopy_from_iter(struct sock *sk, struct iov_iter *from,
struct sk_msg *msg, u32 bytes);
int sk_msg_wait_data(struct sock *sk, struct sk_psock *psock, int flags,
long timeo, int *err);
int sk_msg_recvmsg(struct sock *sk, struct sk_psock *psock, struct msghdr *msg,
int len, int flags);