net: avoid TCP self-connect
Fixes #2690.
R=golang-dev, bradfitz
CC=golang-dev
https://golang.org/cl/5650071
diff --git a/src/pkg/net/dial_test.go b/src/pkg/net/dial_test.go
index f130a11..9196450 100644
--- a/src/pkg/net/dial_test.go
+++ b/src/pkg/net/dial_test.go
@@ -84,3 +84,34 @@
}
}
}
+
+func TestSelfConnect(t *testing.T) {
+ // Test that Dial does not honor self-connects.
+ // See the comment in DialTCP.
+
+ // Find a port that would be used as a local address.
+ l, err := Listen("tcp", "127.0.0.1:0")
+ if err != nil {
+ t.Fatal(err)
+ }
+ c, err := Dial("tcp", l.Addr().String())
+ if err != nil {
+ t.Fatal(err)
+ }
+ addr := c.LocalAddr().String()
+ c.Close()
+ l.Close()
+
+ // Try to connect to that address repeatedly.
+ n := 100000
+ if testing.Short() {
+ n = 1000
+ }
+ for i := 0; i < n; i++ {
+ c, err := Dial("tcp", addr)
+ if err == nil {
+ c.Close()
+ t.Errorf("#%d: Dial %q succeeded", i, addr)
+ }
+ }
+}
diff --git a/src/pkg/net/tcpsock_posix.go b/src/pkg/net/tcpsock_posix.go
index 51a5d6f..200ce91 100644
--- a/src/pkg/net/tcpsock_posix.go
+++ b/src/pkg/net/tcpsock_posix.go
@@ -227,13 +227,43 @@
if raddr == nil {
return nil, &OpError{"dial", net, nil, errMissingAddress}
}
+
fd, err := internetSocket(net, laddr.toAddr(), raddr.toAddr(), syscall.SOCK_STREAM, 0, "dial", sockaddrToTCP)
+
+ // TCP has a rarely used mechanism called a 'simultaneous connection' in
+ // which Dial("tcp", addr1, addr2) run on the machine at addr1 can
+ // connect to a simultaneous Dial("tcp", addr2, addr1) run on the machine
+ // at addr2, without either machine executing Listen. If laddr == nil,
+ // it means we want the kernel to pick an appropriate originating local
+ // address. Some Linux kernels cycle blindly through a fixed range of
+ // local ports, regardless of destination port. If a kernel happens to
+ // pick local port 50001 as the source for a Dial("tcp", "", "localhost:50001"),
+ // then the Dial will succeed, having simultaneously connected to itself.
+ // This can only happen when we are letting the kernel pick a port (laddr == nil)
+ // and when there is no listener for the destination address.
+ // It's hard to argue this is anything other than a kernel bug. If we
+ // see this happen, rather than expose the buggy effect to users, we
+ // close the fd and try again. If it happens twice more, we relent and
+ // use the result. See also:
+ // http://golang.org/issue/2690
+ // http://stackoverflow.com/questions/4949858/
+ for i := 0; i < 2 && err == nil && laddr == nil && selfConnect(fd); i++ {
+ fd.Close()
+ fd, err = internetSocket(net, laddr.toAddr(), raddr.toAddr(), syscall.SOCK_STREAM, 0, "dial", sockaddrToTCP)
+ }
+
if err != nil {
return nil, err
}
return newTCPConn(fd), nil
}
+func selfConnect(fd *netFD) bool {
+ l := fd.laddr.(*TCPAddr)
+ r := fd.raddr.(*TCPAddr)
+ return l.Port == r.Port && l.IP.Equal(r.IP)
+}
+
// TCPListener is a TCP network listener.
// Clients should typically use variables of type Listener
// instead of assuming TCP.
