feature: login program

Cargo.lock

@@ -263,6 +263,7 @@ name = "user"
 version = "0.1.0"
 dependencies = [
  "lazy_static",
+ "libsys",
  "libusr",
 ]
 

Makefile

@@ -92,11 +92,13 @@ initrd:
 		--target=../etc/$(ARCH)-osdev5.json \
 		-Z build-std=core,alloc,compiler_builtins \
 		$(CARGO_COMMON_OPTS)
-	mkdir -p $(O)/rootfs/bin
+	mkdir -p $(O)/rootfs/bin $(O)/rootfs/sbin $(O)/rootfs/dev
+	touch $(O)/rootfs/dev/.do_no_remove
 	cp target/$(ARCH)-osdev5/$(PROFILE)/init $(O)/rootfs/init
 	cp target/$(ARCH)-osdev5/$(PROFILE)/shell $(O)/rootfs/bin
 	cp target/$(ARCH)-osdev5/$(PROFILE)/fuzzy $(O)/rootfs/bin
 	cp target/$(ARCH)-osdev5/$(PROFILE)/ls $(O)/rootfs/bin
+	cp target/$(ARCH)-osdev5/$(PROFILE)/login $(O)/rootfs/sbin
 	cd $(O)/rootfs && tar cf ../initrd.img `find -type f -printf "%P\n"`
 ifeq ($(MACH),orangepi3)
 	$(MKIMAGE) \

fs/vfs/src/ioctx.rs

@@ -1,8 +1,8 @@
 use crate::{FileRef, VnodeKind, VnodeRef};
 use libsys::{
     error::Errno,
-    stat::{OpenFlags, FileMode},
     path::{path_component_left, path_component_right},
+    stat::{FileMode, GroupId, OpenFlags, UserId},
 };
 
 /// I/O context structure
@@ -10,13 +10,17 @@ use libsys::{
 pub struct Ioctx {
     root: VnodeRef,
     cwd: VnodeRef,
+    pub uid: UserId,
+    pub gid: GroupId,
 }
 
 impl Ioctx {
     /// Creates a new I/O context with given root node
-    pub fn new(root: VnodeRef) -> Self {
+    pub fn new(root: VnodeRef, uid: UserId, gid: GroupId) -> Self {
         Self {
             cwd: root.clone(),
+            uid,
+            gid,
             root,
         }
     }
@@ -41,6 +45,11 @@ impl Ioctx {
             }
         }
 
+        while let Some(target) = at.target() {
+            assert!(at.kind() == VnodeKind::Directory);
+            at = target;
+        }
+
         if element.is_empty() && rest.is_empty() {
             return Ok(at);
         }
@@ -113,6 +122,15 @@ impl Ioctx {
 
         node.open(opts)
     }
+
+    pub fn chdir(&mut self, path: &str) -> Result<(), Errno> {
+        let node = self.find(None, path, true)?;
+        if !node.is_directory() {
+            return Err(Errno::NotADirectory);
+        }
+        self.cwd = node;
+        Ok(())
+    }
 }
 
 #[cfg(test)]

fs/vfs/src/node.rs

@@ -105,6 +105,7 @@ impl Vnode {
     pub const SEEKABLE: u32 = 1 << 0;
 
     pub const CACHE_READDIR: u32 = 1 << 1;
+    pub const CACHE_STAT: u32 = 1 << 2;
 
     /// Constructs a new [Vnode], wrapping it in [Rc]. The resulting node
     /// then needs to have [Vnode::set_data()] called on it to be usable.
@@ -452,7 +453,14 @@ impl Vnode {
 
     /// Reports file status
     pub fn stat(self: &VnodeRef) -> Result<Stat, Errno> {
-        if let Some(ref mut data) = *self.data() {
+        if self.flags & Self::CACHE_STAT != 0 {
+            let props = self.props();
+            Ok(Stat {
+                blksize: 0,
+                size: 0,
+                mode: props.mode
+            })
+        } else if let Some(ref mut data) = *self.data() {
             data.stat(self.clone())
         } else {
             Err(Errno::NotImplemented)

kernel/src/fs/devfs.rs

@@ -2,7 +2,7 @@
 use crate::util::InitOnce;
 use alloc::boxed::Box;
 use core::sync::atomic::{AtomicUsize, Ordering};
-use libsys::error::Errno;
+use libsys::{stat::FileMode, error::Errno};
 use vfs::{CharDevice, CharDeviceWrapper, Vnode, VnodeKind, VnodeRef};
 
 /// Possible character device kinds
@@ -16,7 +16,9 @@ static DEVFS_ROOT: InitOnce<VnodeRef> = InitOnce::new();
 
 /// Initializes devfs
 pub fn init() {
-    DEVFS_ROOT.init(Vnode::new("", VnodeKind::Directory, 0));
+    let node = Vnode::new("", VnodeKind::Directory, Vnode::CACHE_READDIR | Vnode::CACHE_STAT);
+    node.props_mut().mode = FileMode::default_dir();
+    DEVFS_ROOT.init(node);
 }
 
 /// Returns devfs root node reference
@@ -27,7 +29,8 @@ pub fn root() -> &'static VnodeRef {
 fn _add_char_device(dev: &'static dyn CharDevice, name: &str) -> Result<(), Errno> {
     infoln!("Add char device: {}", name);
 
-    let node = Vnode::new(name, VnodeKind::Char, 0);
+    let node = Vnode::new(name, VnodeKind::Char, Vnode::CACHE_STAT);
+    node.props_mut().mode = FileMode::from_bits(0o600).unwrap() | FileMode::S_IFCHR;
     node.set_data(Box::new(CharDeviceWrapper::new(dev)));
 
     DEVFS_ROOT.get().attach(node);

kernel/src/fs/mod.rs

@@ -3,6 +3,8 @@ use crate::mem::{
     self,
     phys::{self, PageUsage},
 };
+use libsys::{error::Errno, stat::MountOptions};
+use vfs::VnodeRef;
 use memfs::BlockAllocator;
 
 pub mod devfs;
@@ -25,3 +27,13 @@ unsafe impl BlockAllocator for MemfsBlockAlloc {
         phys::free_page(phys).unwrap();
     }
 }
+
+pub fn create_filesystem(options: &MountOptions) -> Result<VnodeRef, Errno> {
+    let fs_name = options.fs.unwrap();
+
+    if fs_name == "devfs" {
+        Ok(devfs::root().clone())
+    } else {
+        todo!();
+    }
+}

kernel/src/init.rs

@@ -4,7 +4,7 @@ use crate::config::{ConfigKey, CONFIG};
 use crate::fs::{devfs, MemfsBlockAlloc};
 use crate::mem;
 use crate::proc::{elf, Process};
-use libsys::stat::{FileDescriptor, OpenFlags};
+use libsys::stat::{FileDescriptor, OpenFlags, UserId, GroupId};
 use memfs::Ramfs;
 use vfs::{Filesystem, Ioctx};
 
@@ -29,7 +29,7 @@ pub extern "C" fn init_fn(_arg: usize) -> ! {
         unsafe { Ramfs::open(initrd_start as *mut u8, initrd_size, MemfsBlockAlloc {}).unwrap() };
     let root = fs.root().unwrap();
 
-    let ioctx = Ioctx::new(root);
+    let ioctx = Ioctx::new(root, UserId::root(), GroupId::root());
 
     let node = ioctx.find(None, "/init", true).unwrap();
     let file = node.open(OpenFlags::O_RDONLY | OpenFlags::O_EXEC).unwrap();

kernel/src/proc/io.rs

@@ -1,6 +1,6 @@
 //! Process file descriptors and I/O context
 use alloc::collections::BTreeMap;
-use libsys::{error::Errno, stat::FileDescriptor};
+use libsys::{error::Errno, stat::{FileDescriptor, UserId, GroupId}};
 use vfs::{FileRef, Ioctx, VnodeRef, VnodeKind};
 
 /// Process I/O context. Contains file tables, root/cwd info etc.
@@ -31,6 +31,57 @@ impl ProcessIo {
         self.ctty.clone()
     }
 
+    #[inline(always)]
+    pub fn uid(&self) -> UserId {
+        self.ioctx.as_ref().unwrap().uid
+    }
+
+    #[inline(always)]
+    pub fn gid(&self) -> GroupId {
+        self.ioctx.as_ref().unwrap().gid
+    }
+
+    #[inline(always)]
+    pub fn set_uid(&mut self, uid: UserId) -> Result<(), Errno> {
+        let old_uid = self.uid();
+        if old_uid == uid {
+            Ok(())
+        } else if !old_uid.is_root() {
+            Err(Errno::PermissionDenied)
+        } else {
+            self.ioctx.as_mut().unwrap().uid = uid;
+            Ok(())
+        }
+    }
+
+    #[inline(always)]
+    pub fn set_gid(&mut self, gid: GroupId) -> Result<(), Errno> {
+        let old_gid = self.gid();
+        if old_gid == gid {
+            Ok(())
+        } else if !old_gid.is_root() {
+            Err(Errno::PermissionDenied)
+        } else {
+            self.ioctx.as_mut().unwrap().gid = gid;
+            Ok(())
+        }
+    }
+
+    pub fn duplicate_file(&mut self, src: FileDescriptor, dst: Option<FileDescriptor>) -> Result<FileDescriptor, Errno> {
+        let file_ref = self.file(src)?;
+        if let Some(dst) = dst {
+            let idx = u32::from(dst);
+            if self.files.get(&idx).is_some() {
+                return Err(Errno::AlreadyExists);
+            }
+
+            self.files.insert(idx, file_ref);
+            Ok(dst)
+        } else {
+            self.place_file(file_ref)
+        }
+    }
+
     /// Returns [File] struct referred to by file descriptor `idx`
     pub fn file(&mut self, fd: FileDescriptor) -> Result<FileRef, Errno> {
         self.files.get(&u32::from(fd)).cloned().ok_or(Errno::InvalidFile)

kernel/src/proc/process.rs

@@ -82,6 +82,10 @@ impl Process {
         self.inner.lock().pgid = pgid;
     }
 
+    pub fn set_sid(&self, sid: Pid) {
+        self.inner.lock().sid = sid;
+    }
+
     #[inline]
     pub fn current() -> ProcessRef {
         Thread::current().owner().unwrap()

kernel/src/syscall/mod.rs

@@ -3,6 +3,7 @@
 use crate::arch::{machine, platform::exception::ExceptionFrame};
 use crate::debug::Level;
 use crate::dev::timer::TimestampSource;
+use crate::fs::create_filesystem;
 use crate::proc::{self, elf, wait, Process, ProcessIo, Thread};
 use core::mem::size_of;
 use core::ops::DerefMut;
@@ -15,7 +16,8 @@ use libsys::{
     proc::{ExitCode, Pid},
     signal::{Signal, SignalDestination},
     stat::{
-        AccessMode, DirectoryEntry, FdSet, FileDescriptor, FileMode, OpenFlags, Stat, AT_EMPTY_PATH,
+        AccessMode, DirectoryEntry, FdSet, FileDescriptor, FileMode, GroupId, MountOptions,
+        OpenFlags, Stat, UserId, AT_EMPTY_PATH,
     },
     traits::{Read, Write},
 };
@@ -107,7 +109,8 @@ pub fn syscall(num: SystemCall, args: &[usize]) -> Result<usize, Errno> {
 
             let proc = Process::current();
             let mut io = proc.io.lock();
-            let stat = find_at_node(&mut io, at_fd, filename, flags & AT_EMPTY_PATH != 0)?.stat()?;
+            let stat =
+                find_at_node(&mut io, at_fd, filename, flags & AT_EMPTY_PATH != 0)?.stat()?;
             *buf = stat;
             Ok(0)
         }
@@ -153,6 +156,48 @@ pub fn syscall(num: SystemCall, args: &[usize]) -> Result<usize, Errno> {
 
             io.file(fd)?.borrow_mut().readdir(buf)
         }
+        SystemCall::GetUserId => {
+            let proc = Process::current();
+            let uid = proc.io.lock().uid();
+            Ok(u32::from(uid) as usize)
+        }
+        SystemCall::GetGroupId => {
+            let proc = Process::current();
+            let gid = proc.io.lock().gid();
+            Ok(u32::from(gid) as usize)
+        }
+        SystemCall::DuplicateFd => {
+            let src = FileDescriptor::from(args[0] as u32);
+            let dst = FileDescriptor::from_i32(args[1] as i32)?;
+
+            let proc = Process::current();
+            let mut io = proc.io.lock();
+
+            let res = io.duplicate_file(src, dst)?;
+
+            Ok(u32::from(res) as usize)
+        }
+        SystemCall::SetUserId => {
+            let uid = UserId::from(args[0] as u32);
+            let proc = Process::current();
+            proc.io.lock().set_uid(uid)?;
+            Ok(0)
+        }
+        SystemCall::SetGroupId => {
+            let gid = GroupId::from(args[0] as u32);
+            let proc = Process::current();
+            proc.io.lock().set_gid(gid)?;
+            Ok(0)
+        }
+        SystemCall::SetCurrentDirectory => {
+            let path = arg::str_ref(args[0], args[1])?;
+            let proc = Process::current();
+            proc.io.lock().ioctx().chdir(path)?;
+            Ok(0)
+        }
+        SystemCall::GetCurrentDirectory => {
+            todo!()
+        }
 
         // Process
         SystemCall::Clone => {
@@ -294,7 +339,9 @@ pub fn syscall(num: SystemCall, args: &[usize]) -> Result<usize, Errno> {
                 todo!();
             }
 
-            todo!();
+            let id = proc.id();
+            proc.set_sid(id);
+            Ok(id.value() as usize)
         }
         SystemCall::SetPgid => {
             let pid = args[0] as u32;
@@ -317,10 +364,28 @@ pub fn syscall(num: SystemCall, args: &[usize]) -> Result<usize, Errno> {
             let time = machine::local_timer().timestamp()?;
             Ok(time.as_nanos() as usize)
         }
+        SystemCall::Mount => {
+            let target = arg::str_ref(args[0], args[1])?;
+            let options = arg::struct_ref::<MountOptions>(args[2])?;
+
+            let proc = Process::current();
+            let mut io = proc.io.lock();
+
+            debugln!("mount(target={:?}, options={:#x?})", target, options);
+
+            let target_node = io.ioctx().find(None, target, true)?;
+            let root = create_filesystem(options)?;
+
+            target_node.mount(root)?;
+
+            Ok(0)
+        }
 
         // Debugging
         SystemCall::DebugTrace => {
-            let level = TraceLevel::from_repr(args[0]).map(Level::from).ok_or(Errno::InvalidArgument)?;
+            let level = TraceLevel::from_repr(args[0])
+                .map(Level::from)
+                .ok_or(Errno::InvalidArgument)?;
             let buf = arg::str_ref(args[1], args[2])?;
             let thread = Thread::current();
             let proc = thread.owner().unwrap();

libsys/src/abi.rs

@@ -13,6 +13,13 @@ pub enum SystemCall {
     Select = 7,
     Access = 8,
     ReadDirectory = 9,
+    GetUserId = 10,
+    GetGroupId = 11,
+    DuplicateFd = 12,
+    SetUserId = 13,
+    SetGroupId = 14,
+    SetCurrentDirectory = 15,
+    GetCurrentDirectory = 16,
     // Process manipulation
     Fork = 32,
     Clone = 33,
@@ -34,6 +41,7 @@ pub enum SystemCall {
     SetPgid = 49,
     // System
     GetCpuTime = 64,
+    Mount = 65,
     // Debugging
     DebugTrace = 128
 }

libsys/src/calls.rs

@@ -1,11 +1,14 @@
 use crate::abi::SystemCall;
 use crate::{
-    error::Errno,
     debug::TraceLevel,
+    error::Errno,
     ioctl::IoctlCmd,
     proc::{ExitCode, Pid},
     signal::{Signal, SignalDestination},
-    stat::{AccessMode, DirectoryEntry, FdSet, FileDescriptor, FileMode, OpenFlags, Stat},
+    stat::{
+        AccessMode, DirectoryEntry, FdSet, FileDescriptor, FileMode, GroupId, MountOptions,
+        OpenFlags, Stat, UserId,
+    },
 };
 use core::time::Duration;
 
@@ -387,3 +390,64 @@ pub fn sys_readdir(fd: FileDescriptor, buf: &mut [DirectoryEntry]) -> Result<usi
         )
     })
 }
+
+#[inline(always)]
+pub fn sys_getuid() -> UserId {
+    UserId::from(unsafe { syscall!(SystemCall::GetUserId) as u32 })
+}
+
+#[inline(always)]
+pub fn sys_getgid() -> GroupId {
+    GroupId::from(unsafe { syscall!(SystemCall::GetGroupId) as u32 })
+}
+
+#[inline(always)]
+pub fn sys_setsid() -> Result<Pid, Errno> {
+    Errno::from_syscall(unsafe { syscall!(SystemCall::SetSid) })
+        .map(|e| unsafe { Pid::from_raw(e as u32) })
+}
+
+#[inline(always)]
+pub fn sys_mount(target: &str, options: &MountOptions) -> Result<(), Errno> {
+    Errno::from_syscall_unit(unsafe {
+        syscall!(
+            SystemCall::Mount,
+            argp!(target.as_ptr()),
+            argn!(target.len()),
+            argp!(options as *const _)
+        )
+    })
+}
+
+#[inline(always)]
+pub fn sys_dup(src: FileDescriptor, dst: Option<FileDescriptor>) -> Result<FileDescriptor, Errno> {
+    Errno::from_syscall(unsafe {
+        syscall!(
+            SystemCall::DuplicateFd,
+            argn!(u32::from(src)),
+            argn!(FileDescriptor::into_i32(dst))
+        )
+    })
+    .map(|e| FileDescriptor::from(e as u32))
+}
+
+#[inline(always)]
+pub fn sys_setuid(uid: UserId) -> Result<(), Errno> {
+    Errno::from_syscall_unit(unsafe { syscall!(SystemCall::SetUserId, u32::from(uid) as usize) })
+}
+
+#[inline(always)]
+pub fn sys_setgid(gid: GroupId) -> Result<(), Errno> {
+    Errno::from_syscall_unit(unsafe { syscall!(SystemCall::SetGroupId, u32::from(gid) as usize) })
+}
+
+#[inline(always)]
+pub fn sys_chdir(path: &str) -> Result<(), Errno> {
+    Errno::from_syscall_unit(unsafe {
+        syscall!(
+            SystemCall::SetCurrentDirectory,
+            argp!(path.as_ptr()),
+            argn!(path.len())
+        )
+    })
+}

libsys/src/stat.rs

@@ -1,3 +1,4 @@
+// TODO split up this file
 use crate::error::Errno;
 use core::fmt;
 
@@ -15,6 +16,7 @@ bitflags! {
         const O_EXEC =      1 << 5;
         const O_CLOEXEC =   1 << 6;
         const O_DIRECTORY = 1 << 7;
+        const O_CTTY =      1 << 8;
     }
 }
 
@@ -23,6 +25,7 @@ bitflags! {
         const FILE_TYPE = 0xF << 12;
         const S_IFREG = 0x8 << 12;
         const S_IFDIR = 0x4 << 12;
+        const S_IFCHR = 0x2 << 12;
 
         const USER_READ = 1 << 8;
         const USER_WRITE = 1 << 7;
@@ -45,6 +48,69 @@ bitflags! {
     }
 }
 
+#[derive(Clone, Debug)]
+pub struct MountOptions<'a> {
+    pub device: Option<&'a str>,
+    pub fs: Option<&'a str>,
+    // TODO flags etc.
+}
+
+#[derive(Clone, Copy, Debug, PartialEq, Eq, PartialOrd, Ord)]
+#[repr(transparent)]
+pub struct UserId(u32);
+
+#[derive(Clone, Copy, Debug, PartialEq, Eq, PartialOrd, Ord)]
+#[repr(transparent)]
+pub struct GroupId(u32);
+
+impl UserId {
+    pub const fn root() -> Self {
+        Self(0)
+    }
+
+    pub const fn is_root(self) -> bool {
+        self.0 == 0
+    }
+}
+
+impl From<u32> for UserId {
+    #[inline(always)]
+    fn from(v: u32) -> Self {
+        Self(v)
+    }
+}
+
+impl From<UserId> for u32 {
+    #[inline(always)]
+    fn from(v: UserId) -> u32 {
+        v.0
+    }
+}
+
+impl GroupId {
+    pub const fn root() -> Self {
+        Self(0)
+    }
+
+    pub const fn is_root(self) -> bool {
+        self.0 == 0
+    }
+}
+
+impl From<u32> for GroupId {
+    #[inline(always)]
+    fn from(v: u32) -> Self {
+        Self(v)
+    }
+}
+
+impl From<GroupId> for u32 {
+    #[inline(always)]
+    fn from(v: GroupId) -> u32 {
+        v.0
+    }
+}
+
 #[derive(Clone, Default)]
 pub struct FdSet {
     bits: [u64; 2],
@@ -191,6 +257,7 @@ impl fmt::Display for FileMode {
             "{}{}{}{}{}{}{}{}{}{}",
             // File type
             match *self & Self::FILE_TYPE {
+                Self::S_IFCHR => 'c',
                 Self::S_IFDIR => 'd',
                 Self::S_IFREG => '-',
                 _ => '?'

user/Cargo.toml

@@ -21,6 +21,11 @@ path = "src/fuzzy/main.rs"
 name = "ls"
 path = "src/ls/main.rs"
 
+[[bin]]
+name = "login"
+path = "src/login/main.rs"
+
 [dependencies]
 libusr = { path = "../libusr" }
+libsys = { path = "../libsys" }
 lazy_static = { version = "*", features = ["spin_no_std"] }

user/src/init/main.rs

@@ -5,8 +5,19 @@
 #[macro_use]
 extern crate libusr;
 
+use libusr::sys::{stat::MountOptions, sys_execve, sys_fork, sys_mount, sys_waitpid};
+
 #[no_mangle]
 fn main() -> i32 {
+    sys_mount(
+        "/dev",
+        &MountOptions {
+            device: None,
+            fs: Some("devfs"),
+        },
+    )
+    .expect("Failed to mount devfs");
+
     let pid = unsafe { libusr::sys::sys_fork().unwrap() };
 
     if let Some(pid) = pid {
@@ -20,7 +31,7 @@ fn main() -> i32 {
             }
         }
     } else {
-        libusr::sys::sys_execve("/bin/shell", &["/bin/shell"]).unwrap();
+        libusr::sys::sys_execve("/sbin/login", &["/sbin/login", "/dev/ttyS0"]).unwrap();
         loop {}
     }
 }

user/src/login/main.rs

@@ -0,0 +1,151 @@
+#![no_std]
+#![no_main]
+
+#[macro_use]
+extern crate libusr;
+#[macro_use]
+extern crate alloc;
+
+use libsys::{
+    calls::{
+        sys_close, sys_dup, sys_fork, sys_getgid, sys_getpgid, sys_getuid, sys_ioctl, sys_openat,
+        sys_read, sys_setgid, sys_setpgid, sys_setsid, sys_setuid, sys_waitpid, sys_execve
+    },
+    error::Errno,
+    ioctl::IoctlCmd,
+    proc::Pid,
+    stat::{FileDescriptor, FileMode, GroupId, OpenFlags, UserId},
+    termios::{Termios, TermiosLflag},
+};
+use libusr::{env, io};
+
+struct HiddenInput {
+    fd: FileDescriptor,
+    termios: Termios,
+}
+
+impl HiddenInput {
+    fn open(fd: FileDescriptor) -> Result<Self, Errno> {
+        use core::mem::{size_of, MaybeUninit};
+        let mut termios: MaybeUninit<Termios> = MaybeUninit::uninit();
+        sys_ioctl(
+            fd,
+            IoctlCmd::TtyGetAttributes,
+            termios.as_mut_ptr() as usize,
+            size_of::<Termios>(),
+        )?;
+        let termios = unsafe { termios.assume_init() };
+
+        let mut new_termios = termios.clone();
+        new_termios.lflag &= !(TermiosLflag::ECHO | TermiosLflag::ECHOK | TermiosLflag::ECHOE);
+        sys_ioctl(
+            fd,
+            IoctlCmd::TtySetAttributes,
+            &new_termios as *const _ as usize,
+            size_of::<Termios>(),
+        )?;
+
+        Ok(Self { fd, termios })
+    }
+
+    fn readline<'a>(&mut self, buf: &'a mut [u8]) -> Result<&'a str, Errno> {
+        readline(self.fd, buf)
+    }
+}
+
+impl Drop for HiddenInput {
+    fn drop(&mut self) {
+        use core::mem::size_of;
+        sys_ioctl(
+            self.fd,
+            IoctlCmd::TtySetAttributes,
+            &self.termios as *const _ as usize,
+            size_of::<Termios>(),
+        )
+        .ok();
+    }
+}
+
+fn readline(fd: FileDescriptor, buf: &mut [u8]) -> Result<&str, Errno> {
+    let len = sys_read(fd, buf)?;
+
+    if len == 0 {
+        Ok("")
+    } else {
+        Ok(core::str::from_utf8(&buf[..len - 1]).unwrap())
+    }
+}
+
+fn login_as(uid: UserId, gid: GroupId, shell: &str) -> Result<(), Errno> {
+    if let Some(pid) = unsafe { sys_fork() }? {
+        let mut status = 0;
+        sys_waitpid(pid, &mut status).ok();
+        let pgid = sys_getpgid(unsafe { Pid::from_raw(0) }).unwrap();
+        io::tcsetpgrp(FileDescriptor::STDIN, pgid).unwrap();
+        Ok(())
+    } else {
+        sys_setuid(uid).expect("setuid failed");
+        sys_setgid(gid).expect("setgid failed");
+        let pgid = sys_setpgid(unsafe { Pid::from_raw(0) }, unsafe { Pid::from_raw(0) }).unwrap();
+        io::tcsetpgrp(FileDescriptor::STDIN, pgid).unwrap();
+        sys_execve(shell, &[shell]).expect("execve() failed");
+        panic!();
+    }
+}
+
+// TODO baud rate and misc port settings
+#[no_mangle]
+fn main() -> i32 {
+    if !sys_getuid().is_root() {
+        panic!("This program must be run as root");
+    }
+
+    let args = env::args();
+    if args.len() != 2 {
+        panic!("Usage: {} TTY", args[0]);
+    }
+
+    sys_setsid().expect("setsid() failed");
+
+    // Close controlling terminal
+    // NOTE this will invalidate rust-side Stdin, Stdout, Stderr
+    //      until replacement is re-opened using the specified TTY
+    sys_close(FileDescriptor::STDERR).unwrap();
+    sys_close(FileDescriptor::STDOUT).unwrap();
+    sys_close(FileDescriptor::STDIN).unwrap();
+
+    sys_openat(
+        None,
+        args[1],
+        FileMode::default_reg(),
+        OpenFlags::O_RDONLY | OpenFlags::O_CTTY,
+    )
+    .expect("Failed to open stdin");
+    sys_openat(
+        None,
+        args[1],
+        FileMode::default_reg(),
+        OpenFlags::O_WRONLY | OpenFlags::O_CTTY,
+    )
+    .expect("Failed to open stdout");
+    sys_dup(FileDescriptor::STDOUT, Some(FileDescriptor::STDERR)).expect("Failed to open stderr");
+
+    let mut user_buf = [0; 128];
+    let mut password_buf = [0; 128];
+    loop {
+        print!("login: ");
+        let username = readline(FileDescriptor::STDIN, &mut user_buf).expect("Login read failed");
+        print!("password: ");
+        let password = {
+            let mut input = HiddenInput::open(FileDescriptor::STDIN).unwrap();
+            input.readline(&mut password_buf)
+        }
+        .expect("Password read failed");
+
+        if username == "root" && password == "toor" {
+            login_as(UserId::from(0), GroupId::from(0), "/bin/shell");
+        }
+    }
+
+    0
+}

user/src/shell/main.rs

@@ -9,11 +9,34 @@ use alloc::{borrow::ToOwned, vec::Vec};
 use libusr::io::{self, Read};
 use libusr::signal::{self, SignalHandler};
 use libusr::sys::{
-    proc::Pid, sys_execve, sys_setpgid, sys_exit, sys_fork, sys_getpgid, sys_waitpid, Errno, ExitCode,
-    sys_faccessat, AccessMode,
-    FileDescriptor, Signal,
+    proc::Pid, sys_chdir, sys_execve, sys_exit, sys_faccessat, sys_fork, sys_getpgid, sys_setpgid,
+    sys_waitpid, AccessMode, Errno, ExitCode, FileDescriptor, Signal,
 };
 
+struct Builtin {
+    func: fn(&[&str]) -> ExitCode,
+    name: &'static str,
+}
+
+fn cmd_cd(args: &[&str]) -> ExitCode {
+    if args.len() != 2 {
+        eprintln!("Usage: cd DIR");
+        ExitCode::from(-1)
+    } else {
+        if let Err(err) = sys_chdir(args[1]) {
+            eprintln!("{}: {:?}", args[1], err);
+            ExitCode::from(-1)
+        } else {
+            ExitCode::from(0)
+        }
+    }
+}
+
+static BUILTINS: [Builtin; 1] = [Builtin {
+    name: "cd",
+    func: cmd_cd,
+}];
+
 fn readline<'a, F: Read>(f: &mut F, bytes: &'a mut [u8]) -> Result<Option<&'a str>, io::Error> {
     let size = f.read(bytes)?;
     Ok(if size == 0 {
@@ -32,6 +55,12 @@ fn execute(line: &str) -> Result<ExitCode, Errno> {
     let args: Vec<&str> = line.split(' ').collect();
     let cmd = args[0];
 
+    for item in BUILTINS.iter() {
+        if item.name == cmd {
+            return Ok((item.func)(&args));
+        }
+    }
+
     let filename = "/bin/".to_owned() + cmd;
     sys_faccessat(None, &filename, AccessMode::X_OK, 0)?;
 
@@ -73,12 +102,12 @@ fn main() -> i32 {
                 if let Err(e) = execute(line) {
                     eprintln!("{}: {:?}", line.split(' ').next().unwrap(), e);
                 }
-            },
+            }
             Err(_) => {
                 println!("Interrupt!");
                 continue;
-            },
-            _ => panic!()
+            }
+            _ => panic!(),
         }
     }
     0