From: John Fastabend john.fastabend@gmail.com
[ Upstream commit 901546fd8f9ca4b5c481ce00928ab425ce9aacc0 ]
The sockmap code is returning EAGAIN after a FIN packet is received and no more data is on the receive queue. Correct behavior is to return 0 to the user and the user can then close the socket. The EAGAIN causes many apps to retry which masks the problem. Eventually the socket is evicted from the sockmap because its released from sockmap sock free handling. The issue creates a delay and can cause some errors on application side.
To fix this check on sk_msg_recvmsg side if length is zero and FIN flag is set then set return to zero. A selftest will be added to check this condition.
Fixes: 04919bed948dc ("tcp: Introduce tcp_read_skb()") Signed-off-by: John Fastabend john.fastabend@gmail.com Signed-off-by: Daniel Borkmann daniel@iogearbox.net Tested-by: William Findlay will@isovalent.com Reviewed-by: Jakub Sitnicki jakub@cloudflare.com Link: https://lore.kernel.org/bpf/20230523025618.113937-6-john.fastabend@gmail.com Signed-off-by: Sasha Levin sashal@kernel.org --- net/ipv4/tcp_bpf.c | 31 +++++++++++++++++++++++++++++++ 1 file changed, 31 insertions(+)
diff --git a/net/ipv4/tcp_bpf.c b/net/ipv4/tcp_bpf.c index 2e9547467edbe..73c13642d47f6 100644 --- a/net/ipv4/tcp_bpf.c +++ b/net/ipv4/tcp_bpf.c @@ -174,6 +174,24 @@ static int tcp_msg_wait_data(struct sock *sk, struct sk_psock *psock, return ret; }
+static bool is_next_msg_fin(struct sk_psock *psock) +{ + struct scatterlist *sge; + struct sk_msg *msg_rx; + int i; + + msg_rx = sk_psock_peek_msg(psock); + i = msg_rx->sg.start; + sge = sk_msg_elem(msg_rx, i); + if (!sge->length) { + struct sk_buff *skb = msg_rx->skb; + + if (skb && TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN) + return true; + } + return false; +} + static int tcp_bpf_recvmsg_parser(struct sock *sk, struct msghdr *msg, size_t len, @@ -196,6 +214,19 @@ static int tcp_bpf_recvmsg_parser(struct sock *sk, lock_sock(sk); msg_bytes_ready: copied = sk_msg_recvmsg(sk, psock, msg, len, flags); + /* The typical case for EFAULT is the socket was gracefully + * shutdown with a FIN pkt. So check here the other case is + * some error on copy_page_to_iter which would be unexpected. + * On fin return correct return code to zero. + */ + if (copied == -EFAULT) { + bool is_fin = is_next_msg_fin(psock); + + if (is_fin) { + copied = 0; + goto out; + } + } if (!copied) { long timeo; int data;