diff mbox series

[bpf,v5,04/12] bpf: sockmap, handle fin correctly

Message ID 20230406010031.3354-5-john.fastabend@gmail.com (mailing list archive)
State Superseded
Delegated to: BPF
Headers show
Series bpf sockmap fixes | expand

Checks

Context Check Description
netdev/series_format success Posting correctly formatted
netdev/tree_selection success Clearly marked for bpf, async
netdev/fixes_present success Fixes tag present in non-next series
netdev/header_inline success No static functions without inline keyword in header files
netdev/build_32bit success Errors and warnings before: 20 this patch: 20
netdev/cc_maintainers fail 1 blamed authors not CCed: cong.wang@bytedance.com; 5 maintainers not CCed: pabeni@redhat.com dsahern@kernel.org cong.wang@bytedance.com kuba@kernel.org davem@davemloft.net
netdev/build_clang success Errors and warnings before: 18 this patch: 18
netdev/verify_signedoff success Signed-off-by tag matches author and committer
netdev/deprecated_api success None detected
netdev/check_selftest success No net selftest shell script
netdev/verify_fixes success Fixes tag looks correct
netdev/build_allmodconfig_warn success Errors and warnings before: 20 this patch: 20
netdev/checkpatch warning WARNING: Please use correct Fixes: style 'Fixes: <12 chars of sha1> ("<title line>")' - ie: 'Fixes: 04919bed948d ("tcp: Introduce tcp_read_skb()")'
netdev/kdoc success Errors and warnings before: 0 this patch: 0
netdev/source_inline success Was 0 now: 0
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bpf/vmtest-bpf-PR success PR summary
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Commit Message

John Fastabend April 6, 2023, 1 a.m. UTC 
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()")
Tested-by: William Findlay <will@isovalent.com>
Signed-off-by: John Fastabend <john.fastabend@gmail.com>
---
 net/ipv4/tcp_bpf.c | 31 +++++++++++++++++++++++++++++++
 1 file changed, 31 insertions(+)
diff mbox series

Patch

diff --git a/net/ipv4/tcp_bpf.c b/net/ipv4/tcp_bpf.c
index ebf917511937..804bd0c247d0 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;