Separate process waiting from process-reference release to eliminate Windows HANDLE reuse race

cmdline/mingwapp.c

@@ -337,7 +337,9 @@ static int windows_ps(const char* ps_command, char* out, size_t out_size)
 	close(stdout_fd);
 
 	status = 0;
-	if (os_wait(pid, &status) < 0) {
+	pid_t pid_ret = os_wait(pid, &status);
+	os_dispose(pid);
+	if (pid_ret < 0) {
 		log_error(errno, "Failed to wait for PowerShell command '%s' (from os_wait).\n", ps_command);
 		return -1;
 	}

os/mingw.c

@@ -3165,14 +3165,18 @@ pid_t os_wait(pid_t pid, int* status)
 	WaitForSingleObject(h, INFINITE);
 
 	if (GetExitCodeProcess(h, &exit_code)) {
-		CloseHandle(h);
 		*status = exit_code;
 		return pid;
+	} else {
+		windows_errno(GetLastError());
+		return -1;
 	}
+}
 
-	CloseHandle(h);
-
-	return -1;
+void os_dispose(pid_t pid)
+{
+	if (pid > 0)
+		CloseHandle((HANDLE)(intptr_t)pid);
 }
 
 /**

os/os.h

@@ -127,24 +127,33 @@ pid_t os_spawn(char** argv, int* stdout_read_fd, int* stderr_read_fd, const char
 
 /**
  * Wait for the child process to terminate.
- * \param pid Process ID of the child process.
+ * This function does not release the process reference returned by os_spawn().
+ * The caller must eventually call os_dispose().
+ * \param pid Process reference returned by os_spawn().
  * \param status Pointer to store the exit status.
- * \return Child PID on success, -1 on failure.
+ * \return Child process reference on success, -1 on failure.
  */
 pid_t os_wait(pid_t pid, int* status);
 
+/**
+ * Release the process reference returned by os_spawn().
+ * On Unix this is a no-op. On Windows this closes the process HANDLE.
+ * \param pid Process reference returned by os_spawn().
+ */
+void os_dispose(pid_t pid);
+
 /**
  * Terminate gracefully a process. Intended for daemon/service processes controlling child processes.
- * The caller must subsequently call os_wait() to reap process resources and close handles.
- * \param pid Process ID of the process to terminate.
+ * The caller retains ownership and must eventually call both os_wait() and os_dispose() as appropriate.
+ * \param pid Process reference of the process to terminate.
  * \return 0 on success, -1 on failure.
  */
 int os_term(pid_t pid);
 
 /**
  * Forcibly terminate a process.
- * The caller must subsequently call os_wait() to reap process resources and close handles.
- * \param pid Process ID of the process to kill.
+ * The caller retains ownership and must eventually call both os_wait() and os_dispose() as appropriate.
+ * \param pid Process reference of the process to kill.
  * \return 0 on success, -1 on failure.
  */
 int os_kill(pid_t pid);

os/unix.c

@@ -1427,6 +1427,11 @@ pid_t os_wait(pid_t pid, int* status)
 	return ret;
 }
 
+void os_dispose(pid_t pid)
+{
+	(void)pid;
+}
+
 int os_term(pid_t pid)
 {
 	if (pid <= 0) {
@@ -1484,6 +1489,7 @@ int os_spawn_and_wait(const char** argv)
 
 	int status;
 	int ret = os_wait(pid, &status);
+	os_dispose(pid);
 	if (ret == -1) {
 		/* LCOV_EXCL_START */
 		return -1;
@@ -1519,6 +1525,7 @@ OS_FILE* os_popen(const char** argv)
 		close(stdout_fd);
 		int status;
 		os_wait(pid, &status);
+		os_dispose(pid);
 		errno = saved_errno;
 		free(os_file);
 		return 0;
@@ -1547,7 +1554,9 @@ int os_pclose(OS_FILE* stream)
 	fclose(fp);
 
 	int status = 0;
-	if (os_wait(pid, &status) < 0) {
+	int ret = os_wait(pid, &status);
+	os_dispose(pid);
+	if (ret < 0) {
 		return -1;
 	}