Fix race in RunCommandWithOutputForDuration

This function was starting a goroutine that modifies one of its return
values. The intent is for the goroutine to only influence the return
value when it's causing the function to return, but it's racy and can
also modify the return value when the function is returning due to the
timeout. Fix the goroutine to not modify return values directly.

Also, give the channel a buffer so that the goroutine doesn't block
forever after a timeout.

Fixes #18305

Signed-off-by: Aaron Lehmann <aaron.lehmann@docker.com>

integration/utils.go

@@ -104,19 +104,25 @@ func RunCommandWithOutputForDuration(cmd *exec.Cmd, duration time.Duration) (out
 	}
 	cmd.Stderr = &outputBuffer
 
-	done := make(chan error)
-
 	// Start the command in the main thread..
 	err = cmd.Start()
 	if err != nil {
 		err = fmt.Errorf("Fail to start command %v : %v", cmd, err)
 	}
 
+	type exitInfo struct {
+		exitErr  error
+		exitCode int
+	}
+
+	done := make(chan exitInfo, 1)
+
 	go func() {
 		// And wait for it to exit in the goroutine :)
-		exitErr := cmd.Wait()
-		exitCode = ProcessExitCode(exitErr)
-		done <- exitErr
+		info := exitInfo{}
+		info.exitErr = cmd.Wait()
+		info.exitCode = ProcessExitCode(info.exitErr)
+		done <- info
 	}()
 
 	select {
@@ -126,9 +132,9 @@ func RunCommandWithOutputForDuration(cmd *exec.Cmd, duration time.Duration) (out
 			fmt.Printf("failed to kill (pid=%d): %v\n", cmd.Process.Pid, killErr)
 		}
 		timedOut = true
-		break
-	case err = <-done:
-		break
+	case info := <-done:
+		err = info.exitErr
+		exitCode = info.exitCode
 	}
 	output = outputBuffer.String()
 	return