Fix mkdir a/.. should return EEXIST

Before this change `mkdir("a/b/..")` surprisingly makes a directory called `a/b/a`.
It should raise EEXIST.

Author: hoodmane

src/library_fs.js

@@ -290,6 +290,12 @@ FS.staticInit();
       if (errCode) {
         throw new FS.ErrnoError(errCode);
       }
+      if (name === "..") {
+        return parent.parent;
+      }
+      if (name === ".") {
+        return parent;
+      }
       var hash = FS.hashName(parent.id, name);
 #if CASE_INSENSITIVE_FS
       name = name.toLowerCase();
@@ -664,8 +670,8 @@ FS.staticInit();
     mknod(path, mode, dev) {
       var lookup = FS.lookupPath(path, { parent: true });
       var parent = lookup.node;
-      var name = PATH.basename(path);
-      if (!name || name === '.' || name === '..') {
+      var name = path.split('/').filter((p) => !!p && (p !== '.')).at(-1);
+      if (!name) {
         throw new FS.ErrnoError({{{ cDefs.EINVAL }}});
       }
       var errCode = FS.mayCreate(parent, name);

test/fs/test_fs_mkdir_dotdot.c

@@ -0,0 +1,44 @@
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <unistd.h>
+#include <sys/stat.h>
+#include <stdio.h>
+#include <fcntl.h>
+#include <errno.h>
+#include <string.h>
+#include <assert.h>
+#if defined(__EMSCRIPTEN__)
+#include <emscripten.h>
+#endif
+
+void makedir(const char *dir) {
+  int rtn = mkdir(dir, 0777);
+  assert(rtn == 0);
+}
+
+void changedir(const char *dir) {
+  int rtn = chdir(dir);
+  assert(rtn == 0);
+}
+
+void setup() {
+#if defined(__EMSCRIPTEN__) && defined(NODEFS)
+  makedir("working");
+  EM_ASM(FS.mount(NODEFS, { root: '.' }, 'working'));
+  changedir("working");
+#endif
+}
+
+int main() {
+    setup();
+    mkdir("test", 0777);
+    mkdir("test/a", 0777);
+    mkdir("test/a/..", 0777);
+    printf("error: %s\n", strerror(errno));
+    assert(errno == EEXIST);
+    mkdir("test/a/.", 0777);
+    printf("error: %s\n", strerror(errno));
+    assert(errno == EEXIST);
+    printf("success\n");
+}
+

test/test_core.py

@@ -5900,6 +5900,16 @@ def test_fs_rename_on_existing(self, args):
       self.set_setting('FORCE_FILESYSTEM')
     self.do_runf('fs/test_fs_rename_on_existing.c', 'success', emcc_args=args)
 
+  @parameterized({
+    '': ([],),
+    'nodefs': (['-DNODEFS', '-lnodefs.js'],),
+    'noderawfs': (['-sNODERAWFS'],)
+  })
+  def test_fs_mkdir_dotdot(self, args):
+    if self.get_setting('WASMFS'):
+      self.set_setting('FORCE_FILESYSTEM')
+    self.do_runf('fs/test_fs_mkdir_dotdot.c', 'success', emcc_args=args)
+
   def test_sigalrm(self):
     self.do_runf('test_sigalrm.c', 'Received alarm!')
     self.set_setting('EXIT_RUNTIME')