net: in (*netFD).dial, use the passed in local address if getsockname fails

'man getsockname' lists a number of possible failure modes, including
ENOBUFS (for resource exhaustion) and EBADF (which we could possibly
see in the event of a bug or race condition elsewhere in the program).

If getsockname fails for an explicit user-provided local address, the
user is probably not expecting LocalAddr on the returned net.Conn to
return nil. This may or may not fix #34611, but should at least help
us diagnose it more clearly.

While we're add it, also add more nil-checking logic in the test based
on the stack traces posted to
https://golang.org/issue/34611#issuecomment-975923748.

For #34611

Change-Id: Iba870b96787811e4b9959b74ef648afce9316602
Reviewed-on: https://go-review.googlesource.com/c/go/+/366536
Trust: Bryan Mills <bcmills@google.com>
Run-TryBot: Bryan Mills <bcmills@google.com>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>

diff --git a/src/net/server_test.go b/src/net/server_test.go
index 33d33b0337aeb4c2422366b4eaa014c418e9ddf1..b69cd292895f0ba25503d4f2fd000e6124b34f57 100644 (file)
--- a/src/net/server_test.go
+++ b/src/net/server_test.go
@@ -200,9 +200,17 @@ func TestUnixAndUnixpacketServer(t *testing.T) {
                                if c == nil {
                                        panic("Dial returned a nil Conn")
                                }
-                               if rc := reflect.ValueOf(c); rc.Kind() == reflect.Pointer && rc.IsNil() {
+                               rc := reflect.ValueOf(c)
+                               if rc.IsNil() {
                                        panic(fmt.Sprintf("Dial returned a nil %T", c))
                                }
+                               fd := rc.Elem().FieldByName("fd")
+                               if fd.IsNil() {
+                                       panic(fmt.Sprintf("Dial returned a %T with a nil fd", c))
+                               }
+                               if addr := fd.Elem().FieldByName("laddr"); addr.IsNil() {
+                                       panic(fmt.Sprintf("Dial returned a %T whose fd has a nil laddr", c))
+                               }
                                addr := c.LocalAddr()
                                if addr == nil {
                                        panic(fmt.Sprintf("(%T).LocalAddr returned a nil Addr", c))

diff --git a/src/net/sock_posix.go b/src/net/sock_posix.go
index 98a48229c755517e9eff597cae1dfa944feaf5c4..603fb2bb64bbf4b2c65e5f822dd8c028f4c23756 100644 (file)
--- a/src/net/sock_posix.go
+++ b/src/net/sock_posix.go
@@ -156,18 +156,24 @@ func (fd *netFD) dial(ctx context.Context, laddr, raddr sockaddr, ctrlFn func(st
                }
        }
        // Record the local and remote addresses from the actual socket.
-       // Get the local address by calling Getsockname.
+       // For the local address, use
+       // 1) the one returned by Getsockname, if that succeeds; or
+       // 2) the one passed to us as the laddr parameter; or
+       // 3) nil.
        // For the remote address, use
        // 1) the one returned by the connect method, if any; or
        // 2) the one from Getpeername, if it succeeds; or
        // 3) the one passed to us as the raddr parameter.
-       lsa, _ = syscall.Getsockname(fd.pfd.Sysfd)
+       var laddrName Addr = laddr
+       if lsa, err := syscall.Getsockname(fd.pfd.Sysfd); err == nil {
+               laddrName = fd.addrFunc()(lsa)
+       }
        if crsa != nil {
-               fd.setAddr(fd.addrFunc()(lsa), fd.addrFunc()(crsa))
+               fd.setAddr(laddrName, fd.addrFunc()(crsa))
        } else if rsa, _ = syscall.Getpeername(fd.pfd.Sysfd); rsa != nil {
-               fd.setAddr(fd.addrFunc()(lsa), fd.addrFunc()(rsa))
+               fd.setAddr(laddrName, fd.addrFunc()(rsa))
        } else {
-               fd.setAddr(fd.addrFunc()(lsa), raddr)
+               fd.setAddr(laddrName, raddr)
        }
        return nil
 }