Kernel: Use custody_for_dirfd() in more syscalls

This simplifies a lot of syscalls, some of which were doing very
unnecessarily verbose things instead of calling this.

Kernel/Syscalls/chmod.cpp

@@ -17,17 +17,7 @@ ErrorOr<FlatPtr> Process::sys$chmod(Userspace<Syscall::SC_chmod_params const*> u
     TRY(require_promise(Pledge::fattr));
     auto params = TRY(copy_typed_from_user(user_params));
     auto path = TRY(get_syscall_path_argument(params.path));
-
+    auto base = TRY(custody_for_dirfd(params.dirfd));
-    RefPtr<Custody> base;
-    if (params.dirfd == AT_FDCWD) {
-        base = current_directory();
-    } else {
-        auto base_description = TRY(open_file_description(params.dirfd));
-        if (!base_description->custody())
-            return EINVAL;
-        base = base_description->custody();
-    }
-
     TRY(VirtualFileSystem::the().chmod(credentials(), path->view(), params.mode, *base, params.follow_symlinks ? 0 : O_NOFOLLOW_NOERROR));
     return 0;
 }

Kernel/Syscalls/chown.cpp

@@ -27,17 +27,7 @@ ErrorOr<FlatPtr> Process::sys$chown(Userspace<Syscall::SC_chown_params const*> u
     TRY(require_promise(Pledge::chown));
     auto params = TRY(copy_typed_from_user(user_params));
     auto path = TRY(get_syscall_path_argument(params.path));
-
+    auto base = TRY(custody_for_dirfd(params.dirfd));
-    RefPtr<Custody> base;
-    if (params.dirfd == AT_FDCWD) {
-        base = current_directory();
-    } else {
-        auto base_description = TRY(open_file_description(params.dirfd));
-        if (!base_description->custody())
-            return EINVAL;
-        base = base_description->custody();
-    }
-
     TRY(VirtualFileSystem::the().chown(credentials(), path->view(), params.uid, params.gid, *base, params.follow_symlinks ? 0 : O_NOFOLLOW_NOERROR));
     return 0;
 }

Kernel/Syscalls/open.cpp

@@ -55,18 +55,7 @@ ErrorOr<FlatPtr> Process::sys$open(Userspace<Syscall::SC_open_params const*> use
     dbgln_if(IO_DEBUG, "sys$open(dirfd={}, path='{}', options={}, mode={})", dirfd, path->view(), options, mode);
 
     auto fd_allocation = TRY(allocate_fd());
-    RefPtr<Custody> base;
+    auto base = TRY(custody_for_dirfd(dirfd));
-    if (dirfd == AT_FDCWD) {
-        base = current_directory();
-    } else {
-        auto base_description = TRY(open_file_description(dirfd));
-        if (!base_description->is_directory())
-            return ENOTDIR;
-        if (!base_description->custody())
-            return EINVAL;
-        base = base_description->custody();
-    }
-
     auto description = TRY(VirtualFileSystem::the().open(credentials(), path->view(), options, mode & ~umask(), *base));
 
     if (description->inode() && description->inode()->bound_socket())

Kernel/Syscalls/stat.cpp

@@ -28,18 +28,7 @@ ErrorOr<FlatPtr> Process::sys$stat(Userspace<Syscall::SC_stat_params const*> use
     auto params = TRY(copy_typed_from_user(user_params));
 
     auto path = TRY(get_syscall_path_argument(params.path));
-
+    auto base = TRY(custody_for_dirfd(params.dirfd));
-    RefPtr<Custody> base;
-    if (params.dirfd == AT_FDCWD) {
-        base = current_directory();
-    } else {
-        auto base_description = TRY(open_file_description(params.dirfd));
-        if (!base_description->is_directory())
-            return ENOTDIR;
-        if (!base_description->custody())
-            return EINVAL;
-        base = base_description->custody();
-    }
     auto metadata = TRY(VirtualFileSystem::the().lookup_metadata(credentials(), path->view(), *base, params.follow_symlinks ? 0 : O_NOFOLLOW_NOERROR));
     auto statbuf = TRY(metadata.stat());
     TRY(copy_to_user(params.statbuf, &statbuf));

Kernel/Syscalls/unlink.cpp

@@ -19,15 +19,7 @@ ErrorOr<FlatPtr> Process::sys$unlink(int dirfd, Userspace<char const*> user_path
     if (flags & ~AT_REMOVEDIR)
         return Error::from_errno(EINVAL);
 
-    RefPtr<Custody> base;
+    auto base = TRY(custody_for_dirfd(dirfd));
-    if (dirfd == AT_FDCWD) {
-        base = current_directory();
-    } else {
-        auto base_description = TRY(open_file_description(dirfd));
-        if (!base_description->custody())
-            return Error::from_errno(EINVAL);
-        base = base_description->custody();
-    }
 
     if (flags & AT_REMOVEDIR)
         TRY(VirtualFileSystem::the().rmdir(credentials(), path->view(), *base));

Kernel/Syscalls/utimensat.cpp

@@ -19,8 +19,6 @@ ErrorOr<FlatPtr> Process::sys$utimensat(Userspace<Syscall::SC_utimensat_params c
 
     auto params = TRY(copy_typed_from_user(user_params));
     auto now = kgettimeofday().to_timespec();
-
-    int dirfd = params.dirfd;
     int follow_symlink = params.flag & AT_SYMLINK_NOFOLLOW ? O_NOFOLLOW_NOERROR : 0;
 
     timespec times[2];
@@ -37,36 +35,8 @@ ErrorOr<FlatPtr> Process::sys$utimensat(Userspace<Syscall::SC_utimensat_params c
         times[1] = now;
     }
 
-    OwnPtr<KString> path;
+    auto path = TRY(get_syscall_path_argument(params.path));
-    RefPtr<OpenFileDescription> description;
+    auto base = TRY(custody_for_dirfd(params.dirfd));
-    RefPtr<Custody> base;
-
-    auto path_or_error = get_syscall_path_argument(params.path);
-    if (path_or_error.is_error()) {
-        // If the path is empty ("") but not a nullptr, attempt to get a path
-        // from the file descriptor. This allows futimens() to be implemented
-        // in terms of utimensat().
-        if (params.path.characters && params.path.length == 0) {
-            description = TRY(open_file_description(dirfd));
-            path = TRY(description->original_absolute_path());
-            base = description->custody();
-        } else {
-            return path_or_error.release_error();
-        }
-    } else {
-        path = path_or_error.release_value();
-        if (dirfd == AT_FDCWD) {
-            base = current_directory();
-        } else {
-            description = TRY(open_file_description(dirfd));
-            if (!KLexicalPath::is_absolute(path->view()) && !description->is_directory())
-                return ENOTDIR;
-            if (!description->custody())
-                return EINVAL;
-            base = description->custody();
-        }
-    }
-
     auto& atime = times[0];
     auto& mtime = times[1];
     TRY(VirtualFileSystem::the().utimensat(credentials(), path->view(), *base, atime, mtime, follow_symlink));