Android: sdcardfs: Don't do d_add for lower fs

For file based encryption, ext4 explicitly does not
create negative dentries for encrypted files. If you
force one over it, the decrypted file will be hidden
until the cache is cleared. Instead, just fail out.

Signed-off-by: Daniel Rosenberg <drosen@google.com>
Bug: 37231161
Change-Id: Id2a9708dfa75e1c22f89915c529789caadd2ca4b

fs/sdcardfs/lookup.c

@@ -368,17 +368,15 @@ put_name:
 	dname.len = name->len;
 	dname.hash = full_name_hash(dname.name, dname.len);
 	lower_dentry = d_lookup(lower_dir_dentry, &dname);
-	if (lower_dentry)
-		goto setup_lower;
-
-	lower_dentry = d_alloc(lower_dir_dentry, &dname);
 	if (!lower_dentry) {
-		err = -ENOMEM;
+		/* We called vfs_path_lookup earlier, and did not get a negative
+		 * dentry then. Don't confuse the lower filesystem by forcing one
+		 * on it now...
+		 */
+		err = -ENOENT;
 		goto out;
 	}
-	d_add(lower_dentry, NULL); /* instantiate and hash */
 
-setup_lower:
 	lower_path.dentry = lower_dentry;
 	lower_path.mnt = mntget(lower_dir_mnt);
 	sdcardfs_set_lower_path(dentry, &lower_path);