From bd83f0ac993bc5bee0b0f96c74d24cab142ba385 Mon Sep 17 00:00:00 2001
From: "Jason A. Donenfeld" <Jason@zx2c4.com>
Date: Thu, 20 May 2021 18:09:55 +0200
Subject: [PATCH] conn: linux: protect read fds

The -1 protection was removed and the wrong error was returned, causing
us to read from a bogus fd. As well, remove the useless closures that
aren't doing anything, since this is all synchronized anyway.

Fixes: 10533c3 ("all: make conn.Bind.Open return a slice of receive functions")
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
---
 conn/bind_linux.go | 30 ++++++++++++++++++------------
 1 file changed, 18 insertions(+), 12 deletions(-)

diff --git a/conn/bind_linux.go b/conn/bind_linux.go
index c10d8b6..7b970e6 100644
--- a/conn/bind_linux.go
+++ b/conn/bind_linux.go
@@ -148,12 +148,12 @@ again:
 
 	var fns []ReceiveFunc
 	if sock4 != -1 {
-		fns = append(fns, bind.makeReceiveIPv4(sock4))
 		bind.sock4 = sock4
+		fns = append(fns, bind.receiveIPv4)
 	}
 	if sock6 != -1 {
-		fns = append(fns, bind.makeReceiveIPv6(sock6))
 		bind.sock6 = sock6
+		fns = append(fns, bind.receiveIPv6)
 	}
 	if len(fns) == 0 {
 		return nil, 0, syscall.EAFNOSUPPORT
@@ -224,20 +224,26 @@ func (bind *LinuxSocketBind) Close() error {
 	return err2
 }
 
-func (*LinuxSocketBind) makeReceiveIPv6(sock int) ReceiveFunc {
-	return func(buff []byte) (int, Endpoint, error) {
-		var end LinuxSocketEndpoint
-		n, err := receive6(sock, buff, &end)
-		return n, &end, err
+func (bind *LinuxSocketBind) receiveIPv4(buf []byte) (int, Endpoint, error) {
+	bind.mu.RLock()
+	defer bind.mu.RUnlock()
+	if bind.sock4 == -1 {
+		return 0, nil, net.ErrClosed
 	}
+	var end LinuxSocketEndpoint
+	n, err := receive4(bind.sock4, buf, &end)
+	return n, &end, err
 }
 
-func (*LinuxSocketBind) makeReceiveIPv4(sock int) ReceiveFunc {
-	return func(buff []byte) (int, Endpoint, error) {
-		var end LinuxSocketEndpoint
-		n, err := receive4(sock, buff, &end)
-		return n, &end, err
+func (bind *LinuxSocketBind) receiveIPv6(buf []byte) (int, Endpoint, error) {
+	bind.mu.RLock()
+	defer bind.mu.RUnlock()
+	if bind.sock6 == -1 {
+		return 0, nil, net.ErrClosed
 	}
+	var end LinuxSocketEndpoint
+	n, err := receive6(bind.sock6, buf, &end)
+	return n, &end, err
 }
 
 func (bind *LinuxSocketBind) Send(buff []byte, end Endpoint) error {