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.

8 files changed, 64 insertions, 7 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;
 }
 
diff --git a/Userland/Libraries/LibC/unistd.cpp b/Userland/Libraries/LibC/unistd.cpp
index 2c0ba9a8f1..d2a7c134bb 100644
--- a/Userland/Libraries/LibC/unistd.cpp
+++ b/Userland/Libraries/LibC/unistd.cpp
@@ -38,13 +38,24 @@ static __thread int s_cached_tid = 0;
 
 static int s_cached_pid = 0;
 
+int lchown(const char* pathname, uid_t uid, gid_t gid)
+{
+    if (!pathname) {
+        errno = EFAULT;
+        return -1;
+    }
+    Syscall::SC_chown_params params { { pathname, strlen(pathname) }, uid, gid, AT_FDCWD, false };
+    int rc = syscall(SC_chown, &params);
+    __RETURN_WITH_ERRNO(rc, rc, -1);
+}
+
 int chown(const char* pathname, uid_t uid, gid_t gid)
 {
     if (!pathname) {
         errno = EFAULT;
         return -1;
     }
-    Syscall::SC_chown_params params { { pathname, strlen(pathname) }, uid, gid };
+    Syscall::SC_chown_params params { { pathname, strlen(pathname) }, uid, gid, AT_FDCWD, true };
     int rc = syscall(SC_chown, &params);
     __RETURN_WITH_ERRNO(rc, rc, -1);
 }
@@ -55,6 +66,17 @@ int fchown(int fd, uid_t uid, gid_t gid)
     __RETURN_WITH_ERRNO(rc, rc, -1);
 }
 
+int fchownat(int fd, const char* pathname, uid_t uid, gid_t gid, int flags)
+{
+    if (!pathname) {
+        errno = EFAULT;
+        return -1;
+    }
+    Syscall::SC_chown_params params { { pathname, strlen(pathname) }, uid, gid, fd, !(flags & AT_SYMLINK_NOFOLLOW) };
+    int rc = syscall(SC_chown, &params);
+    __RETURN_WITH_ERRNO(rc, rc, -1);
+}
+
 pid_t fork()
 {
     __pthread_fork_prepare();
diff --git a/Userland/Libraries/LibC/unistd.h b/Userland/Libraries/LibC/unistd.h
index 5ed0229809..b12cc237af 100644
--- a/Userland/Libraries/LibC/unistd.h
+++ b/Userland/Libraries/LibC/unistd.h
@@ -104,8 +104,10 @@ int mknod(const char* pathname, mode_t, dev_t);
 long fpathconf(int fd, int name);
 long pathconf(const char* path, int name);
 char* getlogin();
+int lchown(const char* pathname, uid_t uid, gid_t gid);
 int chown(const char* pathname, uid_t, gid_t);
 int fchown(int fd, uid_t, gid_t);
+int fchownat(int fd, const char* pathname, uid_t uid, gid_t gid, int flags);
 int ftruncate(int fd, off_t length);
 int truncate(const char* path, off_t length);
 int mount(int source_fd, const char* target, const char* fs_type, int flags);
diff --git a/Userland/Libraries/LibCore/System.cpp b/Userland/Libraries/LibCore/System.cpp
index f51145fac2..462aa65236 100644
--- a/Userland/Libraries/LibCore/System.cpp
+++ b/Userland/Libraries/LibCore/System.cpp
@@ -368,13 +368,13 @@ ErrorOr<void> fchmod(int fd, mode_t mode)
     return {};
 }
 
-ErrorOr<void> chown(StringView pathname, uid_t uid, gid_t gid)
+ErrorOr<void> lchown(StringView pathname, uid_t uid, gid_t gid)
 {
     if (!pathname.characters_without_null_termination())
         return Error::from_syscall("chown"sv, -EFAULT);
 
 #ifdef __serenity__
-    Syscall::SC_chown_params params = { { pathname.characters_without_null_termination(), pathname.length() }, uid, gid };
+    Syscall::SC_chown_params params = { { pathname.characters_without_null_termination(), pathname.length() }, uid, gid, AT_FDCWD, false };
     int rc = syscall(SC_chown, &params);
     HANDLE_SYSCALL_RETURN_VALUE("chown"sv, rc, {});
 #else
@@ -385,6 +385,23 @@ ErrorOr<void> chown(StringView pathname, uid_t uid, gid_t gid)
 #endif
 }
 
+ErrorOr<void> chown(StringView pathname, uid_t uid, gid_t gid)
+{
+    if (!pathname.characters_without_null_termination())
+        return Error::from_syscall("chown"sv, -EFAULT);
+
+#ifdef __serenity__
+    Syscall::SC_chown_params params = { { pathname.characters_without_null_termination(), pathname.length() }, uid, gid, AT_FDCWD, true };
+    int rc = syscall(SC_chown, &params);
+    HANDLE_SYSCALL_RETURN_VALUE("chown"sv, rc, {});
+#else
+    String path = pathname;
+    if (::lchown(path.characters(), uid, gid) < 0)
+        return Error::from_syscall("lchown"sv, -errno);
+    return {};
+#endif
+}
+
 ErrorOr<Optional<struct passwd>> getpwnam(StringView name)
 {
     ::setpwent();
diff --git a/Userland/Libraries/LibCore/System.h b/Userland/Libraries/LibCore/System.h
index 8ea4b27693..d30457b495 100644
--- a/Userland/Libraries/LibCore/System.h
+++ b/Userland/Libraries/LibCore/System.h
@@ -66,6 +66,7 @@ ErrorOr<void> ioctl(int fd, unsigned request, ...);
 ErrorOr<struct termios> tcgetattr(int fd);
 ErrorOr<void> tcsetattr(int fd, int optional_actions, struct termios const&);
 ErrorOr<void> chmod(StringView pathname, mode_t mode);
+ErrorOr<void> lchown(StringView pathname, uid_t uid, gid_t gid);
 ErrorOr<void> chown(StringView pathname, uid_t uid, gid_t gid);
 ErrorOr<Optional<struct passwd>> getpwnam(StringView name);
 ErrorOr<Optional<struct group>> getgrnam(StringView name);