internal/fuzz: pass handle to temporary file instead of the path

This CL partially reverts CL 297034. Inheritable handles are not
inherited by all workers thanks to using AdditionalInheritedHandles,
which explicitly specifies which handles to inherit by each worker.

This CL doesn't fix any bug, it's more of a cleanup, but also makes
the code more robust and more similar to its Unix counterpart.

Change-Id: I24c2d7f69dfb839a1aeb5858088d8f38b022f702
Reviewed-on: https://go-review.googlesource.com/c/go/+/506535
Reviewed-by: Heschi Kreinick <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>
Run-TryBot: Quim Muntal <[email protected]>
Reviewed-by: Alex Brainman <[email protected]>
Reviewed-by: Bryan Mills <[email protected]>

Author: qmuntal

src/internal/fuzz/sys_windows.go

@@ -85,12 +85,13 @@ func (m *sharedMem) Close() error {
 // run a worker process.
 func setWorkerComm(cmd *exec.Cmd, comm workerComm) {
 	mem := <-comm.memMu
-	memName := mem.f.Name()
+	memFD := mem.f.Fd()
 	comm.memMu <- mem
 	syscall.SetHandleInformation(syscall.Handle(comm.fuzzIn.Fd()), syscall.HANDLE_FLAG_INHERIT, 1)
 	syscall.SetHandleInformation(syscall.Handle(comm.fuzzOut.Fd()), syscall.HANDLE_FLAG_INHERIT, 1)
-	cmd.Env = append(cmd.Env, fmt.Sprintf("GO_TEST_FUZZ_WORKER_HANDLES=%x,%x,%q", comm.fuzzIn.Fd(), comm.fuzzOut.Fd(), memName))
-	cmd.SysProcAttr = &syscall.SysProcAttr{AdditionalInheritedHandles: []syscall.Handle{syscall.Handle(comm.fuzzIn.Fd()), syscall.Handle(comm.fuzzOut.Fd())}}
+	syscall.SetHandleInformation(syscall.Handle(memFD), syscall.HANDLE_FLAG_INHERIT, 1)
+	cmd.Env = append(cmd.Env, fmt.Sprintf("GO_TEST_FUZZ_WORKER_HANDLES=%x,%x,%x", comm.fuzzIn.Fd(), comm.fuzzOut.Fd(), memFD))
+	cmd.SysProcAttr = &syscall.SysProcAttr{AdditionalInheritedHandles: []syscall.Handle{syscall.Handle(comm.fuzzIn.Fd()), syscall.Handle(comm.fuzzOut.Fd()), syscall.Handle(memFD)}}
 }
 
 // getWorkerComm returns communication channels in the worker process.
@@ -99,19 +100,15 @@ func getWorkerComm() (comm workerComm, err error) {
 	if v == "" {
 		return workerComm{}, fmt.Errorf("GO_TEST_FUZZ_WORKER_HANDLES not set")
 	}
-	var fuzzInFD, fuzzOutFD uintptr
-	var memName string
-	if _, err := fmt.Sscanf(v, "%x,%x,%q", &fuzzInFD, &fuzzOutFD, &memName); err != nil {
+	var fuzzInFD, fuzzOutFD, memFileFD uintptr
+	if _, err := fmt.Sscanf(v, "%x,%x,%x", &fuzzInFD, &fuzzOutFD, &memFileFD); err != nil {
 		return workerComm{}, fmt.Errorf("parsing GO_TEST_FUZZ_WORKER_HANDLES=%s: %v", v, err)
 	}
 
 	fuzzIn := os.NewFile(fuzzInFD, "fuzz_in")
 	fuzzOut := os.NewFile(fuzzOutFD, "fuzz_out")
-	tmpFile, err := os.OpenFile(memName, os.O_RDWR, 0)
-	if err != nil {
-		return workerComm{}, fmt.Errorf("worker opening temp file: %w", err)
-	}
-	fi, err := tmpFile.Stat()
+	memFile := os.NewFile(memFileFD, "fuzz_mem")
+	fi, err := memFile.Stat()
 	if err != nil {
 		return workerComm{}, fmt.Errorf("worker checking temp file size: %w", err)
 	}
@@ -120,7 +117,7 @@ func getWorkerComm() (comm workerComm, err error) {
 		return workerComm{}, fmt.Errorf("fuzz temp file exceeds maximum size")
 	}
 	removeOnClose := false
-	mem, err := sharedMemMapFile(tmpFile, size, removeOnClose)
+	mem, err := sharedMemMapFile(memFile, size, removeOnClose)
 	if err != nil {
 		return workerComm{}, err
 	}