Change default umask from 777 to 022 (#22589)

Addresses #17269.

This PR follows the approach made in
#17270 but sets
default `umask` to a more permissive value (`022`). Additionally, it
includes a unit test to cover `umask` functionality.

Author: fluiddot

Diff for: system/lib/libc/emscripten_syscall_stubs.c

@@ -28,7 +28,7 @@ static int g_pid = 42;
 static int g_pgid = 42;
 static int g_ppid = 1;
 static int g_sid = 42;
-static mode_t g_umask = S_IRWXU | S_IRWXG | S_IRWXO;
+static mode_t g_umask = S_IWGRP | S_IWOTH;
 
 #ifdef NDEBUG
 #define REPORT(name)

Diff for: test/other/test_umask.c

@@ -0,0 +1,65 @@
+/*
+ * Copyright 2024 The Emscripten Authors.  All rights reserved.
+ * Emscripten is available under two separate licenses, the MIT license and the
+ * University of Illinois/NCSA Open Source License.  Both these licenses can be
+ * found in the LICENSE file.
+ */
+
+#include <assert.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <signal.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+
+mode_t get_umask() {
+  mode_t current = umask(0);  // Set umask to 0 and get the old value
+  umask(current);  // Immediately set it back
+  return current;
+}
+
+void create_file(const char *path, const char *buffer) {
+  mode_t mode = 0777 - get_umask();
+  int fd = open(path, O_WRONLY | O_CREAT | O_EXCL, mode);
+  assert(fd >= 0);
+
+  int err = write(fd, buffer, sizeof(char) * strlen(buffer));
+  assert(err ==  (sizeof(char) * strlen(buffer)));
+
+  close(fd);
+}
+
+int main() {
+  // Get the default umask
+  mode_t default_umask = get_umask();
+  printf("default umask: %o\n", default_umask);
+  assert(default_umask == 022);
+
+  // Create a new file with default umask
+  create_file("umask_test_file", "abcdef");
+  struct stat st;
+  stat("umask_test_file", &st);
+  printf("default_umask - stat: %o\n", st.st_mode);
+  assert((st.st_mode & 0666) == 0644);
+  unlink("umask_test_file");
+
+  // Set new umask
+  mode_t new_umask = 027;
+  mode_t old_umask = umask(new_umask);
+
+  // Create a new file with new umask
+  create_file("umask_test_file", "abcdef");
+  stat("umask_test_file", &st);
+  printf("new_umask - stat: %o\n", st.st_mode);
+  assert((st.st_mode & 0666) == 0640);
+
+  // Restore the old umask
+  umask(old_umask);
+  
+  puts("success");
+  return EXIT_SUCCESS;
+}

Diff for: test/test_other.py

@@ -7670,6 +7670,11 @@ def test_umask_0(self):
     self.run_process([EMCC, 'src.c'])
     self.assertContained('hello, world!', self.run_js('a.out.js'))
 
+  @crossplatform
+  @also_with_wasmfs
+  def test_umask(self):
+    self.do_runf('other/test_umask.c', 'success')
+
   def test_no_missing_symbols(self):
     # simple hello world should not show any missing symbols
     self.run_process([EMCC, test_file('hello_world.c')])