Make open O_CREATE mode 0 work (#23137)

In nodefs we first create the node with permissions 0 and then try to
open it. The open fails because we don't have read permissions.

The following (18) test expectation files were updated by
running the tests with `--rebaseline`:

```
other/codesize/test_codesize_cxx_ctors1.gzsize: 8351 => 8407 [+56 bytes / +0.67%]
other/codesize/test_codesize_cxx_ctors1.jssize: 20343 => 20486 [+143 bytes / +0.70%]
other/codesize/test_codesize_cxx_ctors2.gzsize: 8334 => 8390 [+56 bytes / +0.67%]
other/codesize/test_codesize_cxx_ctors2.jssize: 20311 => 20454 [+143 bytes / +0.70%]
other/codesize/test_codesize_cxx_except.gzsize: 9356 => 9411 [+55 bytes / +0.59%]
other/codesize/test_codesize_cxx_except.jssize: 24112 => 24255 [+143 bytes / +0.59%]
other/codesize/test_codesize_cxx_except_wasm.gzsize: 8321 => 8373 [+52 bytes / +0.62%]
other/codesize/test_codesize_cxx_except_wasm.jssize: 20236 => 20379 [+143 bytes / +0.71%]
other/codesize/test_codesize_cxx_except_wasm_exnref.gzsize: 8321 => 8373 [+52 bytes / +0.62%]
other/codesize/test_codesize_cxx_except_wasm_exnref.jssize: 20236 => 20379 [+143 bytes / +0.71%]
other/codesize/test_codesize_cxx_lto.gzsize: 8347 => 8404 [+57 bytes / +0.68%]
other/codesize/test_codesize_cxx_lto.jssize: 20367 => 20510 [+143 bytes / +0.70%]
other/codesize/test_codesize_cxx_mangle.gzsize: 9359 => 9416 [+57 bytes / +0.61%]
other/codesize/test_codesize_cxx_mangle.jssize: 24112 => 24255 [+143 bytes / +0.59%]
other/codesize/test_codesize_cxx_noexcept.gzsize: 8351 => 8407 [+56 bytes / +0.67%]
other/codesize/test_codesize_cxx_noexcept.jssize: 20343 => 20486 [+143 bytes / +0.70%]
other/codesize/test_codesize_files_js_fs.gzsize: 7654 => 7702 [+48 bytes / +0.63%]
other/codesize/test_codesize_files_js_fs.jssize: 18838 => 18980 [+142 bytes / +0.75%]

Average change: +0.66% (+0.59% - +0.75%)
```

src/library_fs.js

@@ -1087,7 +1087,10 @@ FS.staticInit();
           throw new FS.ErrnoError({{{ cDefs.EISDIR }}});
         } else {
           // node doesn't exist, try to create it
-          node = FS.mknod(path, mode, 0);
+          // Ignore the permission bits here to ensure we can `open` this new
+          // file below. We use chmod below the apply the permissions once the
+          // file is open.
+          node = FS.mknod(path, mode | 0o777, 0);
           created = true;
         }
       }
@@ -1137,6 +1140,9 @@ FS.staticInit();
       if (stream.stream_ops.open) {
         stream.stream_ops.open(stream);
       }
+      if (created) {
+        FS.chmod(node, mode & 0o777);
+      }
 #if expectToReceiveOnModule('logReadFiles')
       if (Module['logReadFiles'] && !(flags & {{{ cDefs.O_WRONLY}}})) {
         if (!(path in FS.readFiles)) {

test/fs/test_fs_open_no_permissions.c

@@ -0,0 +1,21 @@
+#include <stdio.h>
+#include <unistd.h>
+#include <assert.h>
+#include <fcntl.h>
+#include <string.h>
+#include <sys/stat.h>
+#include <assert.h>
+#include <errno.h>
+#include <string.h>
+
+// TODO: Combine this with test_fcntl_open.c. First requires fixing
+// test_fcntl_open.c on noderawfs.
+int main() {
+  int res = open("a", O_CREAT, 0);
+  printf("error: %s\n", strerror(errno));
+  assert(res >= 0);
+  struct stat st;
+  assert(stat("a", &st) == 0);
+  assert((st.st_mode & 0777) == 0);
+  printf("success\n");
+}

test/other/codesize/test_codesize_cxx_ctors1.gzsize

@@ -1 +1 @@
-8351
+8407

test/other/codesize/test_codesize_cxx_ctors1.jssize

@@ -1 +1 @@
-20343
+20486

test/other/codesize/test_codesize_cxx_ctors2.gzsize

@@ -1 +1 @@
-8334
+8390

test/other/codesize/test_codesize_cxx_ctors2.jssize

@@ -1 +1 @@
-20311
+20454

test/other/codesize/test_codesize_cxx_except.gzsize

@@ -1 +1 @@
-9356
+9411

test/other/codesize/test_codesize_cxx_except.jssize

@@ -1 +1 @@
-24112
+24255

test/other/codesize/test_codesize_cxx_except_wasm.gzsize

@@ -1 +1 @@
-8321
+8373

test/other/codesize/test_codesize_cxx_except_wasm.jssize

@@ -1 +1 @@
-20236
+20379

test/other/codesize/test_codesize_cxx_except_wasm_exnref.gzsize

@@ -1 +1 @@
-8321
+8373

test/other/codesize/test_codesize_cxx_except_wasm_exnref.jssize

@@ -1 +1 @@
-20236
+20379

test/other/codesize/test_codesize_cxx_lto.gzsize

@@ -1 +1 @@
-8347
+8404

test/other/codesize/test_codesize_cxx_lto.jssize

@@ -1 +1 @@
-20367
+20510

test/other/codesize/test_codesize_cxx_mangle.gzsize

@@ -1 +1 @@
-9359
+9416

test/other/codesize/test_codesize_cxx_mangle.jssize

@@ -1 +1 @@
-24112
+24255

test/other/codesize/test_codesize_cxx_noexcept.gzsize

@@ -1 +1 @@
-8351
+8407

test/other/codesize/test_codesize_cxx_noexcept.jssize

@@ -1 +1 @@
-20343
+20486

test/other/codesize/test_codesize_files_js_fs.gzsize

@@ -1 +1 @@
-7654
+7702

test/other/codesize/test_codesize_files_js_fs.jssize

@@ -1 +1 @@
-18838
+18980

test/test_core.py

@@ -5858,6 +5858,10 @@ def test_fs_rename_on_existing(self):
       self.set_setting('FORCE_FILESYSTEM')
     self.do_runf('fs/test_fs_rename_on_existing.c', 'success')
 
+  @also_with_nodefs_both
+  def test_fs_open_no_permissions(self):
+    self.do_runf('fs/test_fs_open_no_permissions.c', 'success')
+
   @also_with_nodefs_both
   @crossplatform
   @no_windows('https://github.com/emscripten-core/emscripten/issues/8882')