Kernel+LibC+LibCore: Add lchown and fchownat functions

This modifies sys$chown to allow specifying whether or not to follow
symlinks and in which directory.

This was then used to implement lchown and fchownat in LibC and LibCore.

4 files changed, 19 insertions, 4 deletions

diff --git a/Kernel/API/Syscall.h b/Kernel/API/Syscall.h
index 6372efb165..d02184fdfd 100644
--- a/Kernel/API/Syscall.h
+++ b/Kernel/API/Syscall.h
@@ -400,6 +400,8 @@ struct SC_chown_params {
     StringArgument path;
     u32 uid;
     u32 gid;
+    int dirfd;
+    int follow_symlinks;
 };
 
 struct SC_mknod_params {
diff --git a/Kernel/FileSystem/VirtualFileSystem.cpp b/Kernel/FileSystem/VirtualFileSystem.cpp
index 3855182999..2bcf342329 100644
--- a/Kernel/FileSystem/VirtualFileSystem.cpp
+++ b/Kernel/FileSystem/VirtualFileSystem.cpp
@@ -564,9 +564,9 @@ ErrorOr<void> VirtualFileSystem::chown(Custody& custody, UserID a_uid, GroupID a
     return inode.chown(new_uid, new_gid);
 }
 
-ErrorOr<void> VirtualFileSystem::chown(StringView path, UserID a_uid, GroupID a_gid, Custody& base)
+ErrorOr<void> VirtualFileSystem::chown(StringView path, UserID a_uid, GroupID a_gid, Custody& base, int options)
 {
-    auto custody = TRY(resolve_path(path, base));
+    auto custody = TRY(resolve_path(path, base, nullptr, options));
     return chown(custody, a_uid, a_gid);
 }
 
diff --git a/Kernel/FileSystem/VirtualFileSystem.h b/Kernel/FileSystem/VirtualFileSystem.h
index bee3f1504f..a1386dbb14 100644
--- a/Kernel/FileSystem/VirtualFileSystem.h
+++ b/Kernel/FileSystem/VirtualFileSystem.h
@@ -59,7 +59,7 @@ public:
     ErrorOr<void> rmdir(StringView path, Custody& base);
     ErrorOr<void> chmod(StringView path, mode_t, Custody& base);
     ErrorOr<void> chmod(Custody&, mode_t);
-    ErrorOr<void> chown(StringView path, UserID, GroupID, Custody& base);
+    ErrorOr<void> chown(StringView path, UserID, GroupID, Custody& base, int options);
     ErrorOr<void> chown(Custody&, UserID, GroupID);
     ErrorOr<void> access(StringView path, int mode, Custody& base);
     ErrorOr<InodeMetadata> lookup_metadata(StringView path, Custody& base, int options = 0);
diff --git a/Kernel/Syscalls/chown.cpp b/Kernel/Syscalls/chown.cpp
index 92172fed61..0db2c9cccc 100644
--- a/Kernel/Syscalls/chown.cpp
+++ b/Kernel/Syscalls/chown.cpp
@@ -4,6 +4,8 @@
  * SPDX-License-Identifier: BSD-2-Clause
  */
 
+#include <AK/NonnullRefPtrVector.h>
+#include <Kernel/FileSystem/Custody.h>
 #include <Kernel/FileSystem/OpenFileDescription.h>
 #include <Kernel/Process.h>
 
@@ -24,7 +26,18 @@ ErrorOr<FlatPtr> Process::sys$chown(Userspace<const Syscall::SC_chown_params*> u
     TRY(require_promise(Pledge::chown));
     auto params = TRY(copy_typed_from_user(user_params));
     auto path = TRY(get_syscall_path_argument(params.path));
-    TRY(VirtualFileSystem::the().chown(path->view(), params.uid, params.gid, current_directory()));
+
+    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().chown(path->view(), params.uid, params.gid, *base, params.follow_symlinks ? 0 : O_NOFOLLOW_NOERROR));
     return 0;
 }