Kernel+LibC+LibCore+UE: Implement `fchmodat(2)`

This function is an extended version of `chmod(2)` that lets one control
whether to dereference symlinks, and specify a file descriptor to a
directory that will be used as the base for relative paths.

1 files changed, 16 insertions, 3 deletions

diff --git a/Kernel/Syscalls/chmod.cpp b/Kernel/Syscalls/chmod.cpp
index 34af280f07..9b79682afd 100644
--- a/Kernel/Syscalls/chmod.cpp
+++ b/Kernel/Syscalls/chmod.cpp
@@ -1,5 +1,6 @@
 /*
  * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
+ * Copyright (c) 2022, Daniel Bertalan <dani@danielbertalan.dev>
  *
  * SPDX-License-Identifier: BSD-2-Clause
  */
@@ -10,12 +11,24 @@
 
 namespace Kernel {
 
-ErrorOr<FlatPtr> Process::sys$chmod(Userspace<const char*> user_path, size_t path_length, mode_t mode)
+ErrorOr<FlatPtr> Process::sys$chmod(Userspace<Syscall::SC_chmod_params const*> user_params)
 {
     VERIFY_PROCESS_BIG_LOCK_ACQUIRED(this);
     TRY(require_promise(Pledge::fattr));
-    auto path = TRY(get_syscall_path_argument(user_path, path_length));
-    TRY(VirtualFileSystem::the().chmod(path->view(), mode, current_directory()));
+    auto params = TRY(copy_typed_from_user(user_params));
+    auto path = TRY(get_syscall_path_argument(params.path));
+
+    RefPtr<Custody> base;
+    if (params.dirfd == AT_FDCWD) {
+        base = current_directory();
+    } else {
+        auto base_description = TRY(fds().open_file_description(params.dirfd));
+        if (!base_description->custody())
+            return EINVAL;
+        base = base_description->custody();
+    }
+
+    TRY(VirtualFileSystem::the().chmod(path->view(), params.mode, *base, params.follow_symlinks ? 0 : O_NOFOLLOW_NOERROR));
     return 0;
 }