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unix: in Linux sendmsgN actually send one normal byte
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A bug in CL 412497 caused us to set up an iovec for a dummy byte
but fail to use it

Fixes golang/go#56384

Change-Id: If56fea5c47e5c6fac92f9707d4c3dd78f7999a65
Reviewed-on: https://go-review.googlesource.com/c/sys/+/445255
TryBot-Result: Gopher Robot <[email protected]>
Reviewed-by: Ian Lance Taylor <[email protected]>
Reviewed-by: Tobias Klauser <[email protected]>
Auto-Submit: Ian Lance Taylor <[email protected]>
Run-TryBot: Ian Lance Taylor <[email protected]>
Run-TryBot: Ian Lance Taylor <[email protected]>
Reviewed-by: Heschi Kreinick <[email protected]>
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ianlancetaylor authored and gopherbot committed Oct 25, 2022
1 parent 95e765b commit 5726498
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1 change: 1 addition & 0 deletions unix/syscall_linux.go
Original file line number Diff line number Diff line change
Expand Up @@ -1554,6 +1554,7 @@ func sendmsgN(fd int, iov []Iovec, oob []byte, ptr unsafe.Pointer, salen _Sockle
var iova [1]Iovec
iova[0].Base = &dummy
iova[0].SetLen(1)
iov = iova[:]
}
}
msg.Control = &oob[0]
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96 changes: 96 additions & 0 deletions unix/syscall_unix_test.go
Original file line number Diff line number Diff line change
Expand Up @@ -1015,6 +1015,102 @@ func TestSendmsgBuffers(t *testing.T) {
}
}

// Issue 56384.
func TestRecvmsgControl(t *testing.T) {
switch runtime.GOOS {
case "solaris", "illumos":
// Test fails on Solaris, saying
// "got 0 control messages, want 1".
// Not sure why; Solaris recvmsg man page says
// "For processes on the same host, recvmsg() can be
// used to receive a file descriptor from another
// process, but it cannot receive ancillary data."
t.Skipf("skipping on %s", runtime.GOOS)
}

fds, err := unix.Socketpair(unix.AF_UNIX, unix.SOCK_STREAM, 0)
if err != nil {
t.Fatal(err)
}
defer unix.Close(fds[0])
defer unix.Close(fds[1])

const payload = "hello"

// Start a goroutine that sends a control message followed by
// a payload on fds[1].
go func() {
f, err := os.Create(filepath.Join(t.TempDir(), "file"))
if err != nil {
t.Error(err)
return
}
defer f.Close()

rc, err := f.SyscallConn()
if err != nil {
t.Error(err)
return
}
var rights []byte
err = rc.Control(func(fd uintptr) {
rights = unix.UnixRights(int(fd))
})
if err != nil {
t.Error(err)
return
}

_, err = unix.SendmsgN(fds[1], nil, rights, nil, 0)
if err != nil {
t.Error(err)
}
if _, err := unix.Write(fds[1], []byte(payload)); err != nil {
t.Error(err)
}
}()

// Read the control message sent by the goroutine. The
// goroutine writes to fds[1], we read from fds[0].

cbuf := make([]byte, unix.CmsgSpace(4))
_, cn, _, _, err := unix.Recvmsg(fds[0], nil, cbuf, 0)
if err != nil {
t.Fatal(err)
}
cbuf = cbuf[:cn]

// Read the payload sent by the goroutine.

buf := make([]byte, len(payload))
n, err := unix.Read(fds[0], buf)
if err != nil {
t.Fatal(err)
}
buf = buf[:n]
if payload != string(buf) {
t.Errorf("read payload %q, want %q", buf, payload)
}

// Check the control message.

cmsgs, err := unix.ParseSocketControlMessage(cbuf)
if err != nil {
t.Fatal(err)
}
if len(cmsgs) != 1 {
t.Fatalf("got %d control messages, want 1", len(cmsgs))
}
cfds, err := unix.ParseUnixRights(&cmsgs[0])
if err != nil {
t.Fatal(err)
}
if len(cfds) != 1 {
t.Fatalf("got %d fds, want 1", len(cfds))
}
defer unix.Close(cfds[0])
}

// mktmpfifo creates a temporary FIFO and provides a cleanup function.
func mktmpfifo(t *testing.T) (*os.File, func()) {
err := unix.Mkfifo("fifo", 0666)
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