| // SPDX-License-Identifier: GPL-2.0 |
| |
| //! Tasks (threads and processes). |
| //! |
| //! C header: [`include/linux/sched.h`](srctree/include/linux/sched.h). |
| |
| use crate::{ |
| bindings, |
| ffi::{c_int, c_long, c_uint}, |
| pid_namespace::PidNamespace, |
| types::{ARef, NotThreadSafe, Opaque}, |
| }; |
| use core::{ |
| cmp::{Eq, PartialEq}, |
| ops::Deref, |
| ptr, |
| }; |
| |
| /// A sentinel value used for infinite timeouts. |
| pub const MAX_SCHEDULE_TIMEOUT: c_long = c_long::MAX; |
| |
| /// Bitmask for tasks that are sleeping in an interruptible state. |
| pub const TASK_INTERRUPTIBLE: c_int = bindings::TASK_INTERRUPTIBLE as c_int; |
| /// Bitmask for tasks that are sleeping in an uninterruptible state. |
| pub const TASK_UNINTERRUPTIBLE: c_int = bindings::TASK_UNINTERRUPTIBLE as c_int; |
| /// Bitmask for tasks that are sleeping in a freezable state. |
| pub const TASK_FREEZABLE: c_int = bindings::TASK_FREEZABLE as c_int; |
| /// Convenience constant for waking up tasks regardless of whether they are in interruptible or |
| /// uninterruptible sleep. |
| pub const TASK_NORMAL: c_uint = bindings::TASK_NORMAL as c_uint; |
| |
| /// Returns the currently running task. |
| #[macro_export] |
| macro_rules! current { |
| () => { |
| // SAFETY: Deref + addr-of below create a temporary `TaskRef` that cannot outlive the |
| // caller. |
| unsafe { &*$crate::task::Task::current() } |
| }; |
| } |
| |
| /// Returns the currently running task's pid namespace. |
| #[macro_export] |
| macro_rules! current_pid_ns { |
| () => { |
| // SAFETY: Deref + addr-of below create a temporary `PidNamespaceRef` that cannot outlive |
| // the caller. |
| unsafe { &*$crate::task::Task::current_pid_ns() } |
| }; |
| } |
| |
| /// Wraps the kernel's `struct task_struct`. |
| /// |
| /// # Invariants |
| /// |
| /// All instances are valid tasks created by the C portion of the kernel. |
| /// |
| /// Instances of this type are always refcounted, that is, a call to `get_task_struct` ensures |
| /// that the allocation remains valid at least until the matching call to `put_task_struct`. |
| /// |
| /// # Examples |
| /// |
| /// The following is an example of getting the PID of the current thread with zero additional cost |
| /// when compared to the C version: |
| /// |
| /// ``` |
| /// let pid = current!().pid(); |
| /// ``` |
| /// |
| /// Getting the PID of the current process, also zero additional cost: |
| /// |
| /// ``` |
| /// let pid = current!().group_leader().pid(); |
| /// ``` |
| /// |
| /// Getting the current task and storing it in some struct. The reference count is automatically |
| /// incremented when creating `State` and decremented when it is dropped: |
| /// |
| /// ``` |
| /// use kernel::{task::Task, types::ARef}; |
| /// |
| /// struct State { |
| /// creator: ARef<Task>, |
| /// index: u32, |
| /// } |
| /// |
| /// impl State { |
| /// fn new() -> Self { |
| /// Self { |
| /// creator: current!().into(), |
| /// index: 0, |
| /// } |
| /// } |
| /// } |
| /// ``` |
| #[repr(transparent)] |
| pub struct Task(pub(crate) Opaque<bindings::task_struct>); |
| |
| // SAFETY: By design, the only way to access a `Task` is via the `current` function or via an |
| // `ARef<Task>` obtained through the `AlwaysRefCounted` impl. This means that the only situation in |
| // which a `Task` can be accessed mutably is when the refcount drops to zero and the destructor |
| // runs. It is safe for that to happen on any thread, so it is ok for this type to be `Send`. |
| unsafe impl Send for Task {} |
| |
| // SAFETY: It's OK to access `Task` through shared references from other threads because we're |
| // either accessing properties that don't change (e.g., `pid`, `group_leader`) or that are properly |
| // synchronised by C code (e.g., `signal_pending`). |
| unsafe impl Sync for Task {} |
| |
| /// The type of process identifiers (PIDs). |
| pub type Pid = bindings::pid_t; |
| |
| /// The type of user identifiers (UIDs). |
| #[derive(Copy, Clone)] |
| pub struct Kuid { |
| kuid: bindings::kuid_t, |
| } |
| |
| impl Task { |
| /// Returns a raw pointer to the current task. |
| /// |
| /// It is up to the user to use the pointer correctly. |
| #[inline] |
| pub fn current_raw() -> *mut bindings::task_struct { |
| // SAFETY: Getting the current pointer is always safe. |
| unsafe { bindings::get_current() } |
| } |
| |
| /// Returns a task reference for the currently executing task/thread. |
| /// |
| /// The recommended way to get the current task/thread is to use the |
| /// [`current`] macro because it is safe. |
| /// |
| /// # Safety |
| /// |
| /// Callers must ensure that the returned object doesn't outlive the current task/thread. |
| pub unsafe fn current() -> impl Deref<Target = Task> { |
| struct TaskRef<'a> { |
| task: &'a Task, |
| _not_send: NotThreadSafe, |
| } |
| |
| impl Deref for TaskRef<'_> { |
| type Target = Task; |
| |
| fn deref(&self) -> &Self::Target { |
| self.task |
| } |
| } |
| |
| let current = Task::current_raw(); |
| TaskRef { |
| // SAFETY: If the current thread is still running, the current task is valid. Given |
| // that `TaskRef` is not `Send`, we know it cannot be transferred to another thread |
| // (where it could potentially outlive the caller). |
| task: unsafe { &*current.cast() }, |
| _not_send: NotThreadSafe, |
| } |
| } |
| |
| /// Returns a PidNamespace reference for the currently executing task's/thread's pid namespace. |
| /// |
| /// This function can be used to create an unbounded lifetime by e.g., storing the returned |
| /// PidNamespace in a global variable which would be a bug. So the recommended way to get the |
| /// current task's/thread's pid namespace is to use the [`current_pid_ns`] macro because it is |
| /// safe. |
| /// |
| /// # Safety |
| /// |
| /// Callers must ensure that the returned object doesn't outlive the current task/thread. |
| pub unsafe fn current_pid_ns() -> impl Deref<Target = PidNamespace> { |
| struct PidNamespaceRef<'a> { |
| task: &'a PidNamespace, |
| _not_send: NotThreadSafe, |
| } |
| |
| impl Deref for PidNamespaceRef<'_> { |
| type Target = PidNamespace; |
| |
| fn deref(&self) -> &Self::Target { |
| self.task |
| } |
| } |
| |
| // The lifetime of `PidNamespace` is bound to `Task` and `struct pid`. |
| // |
| // The `PidNamespace` of a `Task` doesn't ever change once the `Task` is alive. A |
| // `unshare(CLONE_NEWPID)` or `setns(fd_pidns/pidfd, CLONE_NEWPID)` will not have an effect |
| // on the calling `Task`'s pid namespace. It will only effect the pid namespace of children |
| // created by the calling `Task`. This invariant guarantees that after having acquired a |
| // reference to a `Task`'s pid namespace it will remain unchanged. |
| // |
| // When a task has exited and been reaped `release_task()` will be called. This will set |
| // the `PidNamespace` of the task to `NULL`. So retrieving the `PidNamespace` of a task |
| // that is dead will return `NULL`. Note, that neither holding the RCU lock nor holding a |
| // referencing count to |
| // the `Task` will prevent `release_task()` being called. |
| // |
| // In order to retrieve the `PidNamespace` of a `Task` the `task_active_pid_ns()` function |
| // can be used. There are two cases to consider: |
| // |
| // (1) retrieving the `PidNamespace` of the `current` task |
| // (2) retrieving the `PidNamespace` of a non-`current` task |
| // |
| // From system call context retrieving the `PidNamespace` for case (1) is always safe and |
| // requires neither RCU locking nor a reference count to be held. Retrieving the |
| // `PidNamespace` after `release_task()` for current will return `NULL` but no codepath |
| // like that is exposed to Rust. |
| // |
| // Retrieving the `PidNamespace` from system call context for (2) requires RCU protection. |
| // Accessing `PidNamespace` outside of RCU protection requires a reference count that |
| // must've been acquired while holding the RCU lock. Note that accessing a non-`current` |
| // task means `NULL` can be returned as the non-`current` task could have already passed |
| // through `release_task()`. |
| // |
| // To retrieve (1) the `current_pid_ns!()` macro should be used which ensure that the |
| // returned `PidNamespace` cannot outlive the calling scope. The associated |
| // `current_pid_ns()` function should not be called directly as it could be abused to |
| // created an unbounded lifetime for `PidNamespace`. The `current_pid_ns!()` macro allows |
| // Rust to handle the common case of accessing `current`'s `PidNamespace` without RCU |
| // protection and without having to acquire a reference count. |
| // |
| // For (2) the `task_get_pid_ns()` method must be used. This will always acquire a |
| // reference on `PidNamespace` and will return an `Option` to force the caller to |
| // explicitly handle the case where `PidNamespace` is `None`, something that tends to be |
| // forgotten when doing the equivalent operation in `C`. Missing RCU primitives make it |
| // difficult to perform operations that are otherwise safe without holding a reference |
| // count as long as RCU protection is guaranteed. But it is not important currently. But we |
| // do want it in the future. |
| // |
| // Note for (2) the required RCU protection around calling `task_active_pid_ns()` |
| // synchronizes against putting the last reference of the associated `struct pid` of |
| // `task->thread_pid`. The `struct pid` stored in that field is used to retrieve the |
| // `PidNamespace` of the caller. When `release_task()` is called `task->thread_pid` will be |
| // `NULL`ed and `put_pid()` on said `struct pid` will be delayed in `free_pid()` via |
| // `call_rcu()` allowing everyone with an RCU protected access to the `struct pid` acquired |
| // from `task->thread_pid` to finish. |
| // |
| // SAFETY: The current task's pid namespace is valid as long as the current task is running. |
| let pidns = unsafe { bindings::task_active_pid_ns(Task::current_raw()) }; |
| PidNamespaceRef { |
| // SAFETY: If the current thread is still running, the current task and its associated |
| // pid namespace are valid. `PidNamespaceRef` is not `Send`, so we know it cannot be |
| // transferred to another thread (where it could potentially outlive the current |
| // `Task`). The caller needs to ensure that the PidNamespaceRef doesn't outlive the |
| // current task/thread. |
| task: unsafe { PidNamespace::from_ptr(pidns) }, |
| _not_send: NotThreadSafe, |
| } |
| } |
| |
| /// Returns a raw pointer to the task. |
| #[inline] |
| pub fn as_ptr(&self) -> *mut bindings::task_struct { |
| self.0.get() |
| } |
| |
| /// Returns the group leader of the given task. |
| pub fn group_leader(&self) -> &Task { |
| // SAFETY: The group leader of a task never changes after initialization, so reading this |
| // field is not a data race. |
| let ptr = unsafe { *ptr::addr_of!((*self.as_ptr()).group_leader) }; |
| |
| // SAFETY: The lifetime of the returned task reference is tied to the lifetime of `self`, |
| // and given that a task has a reference to its group leader, we know it must be valid for |
| // the lifetime of the returned task reference. |
| unsafe { &*ptr.cast() } |
| } |
| |
| /// Returns the PID of the given task. |
| pub fn pid(&self) -> Pid { |
| // SAFETY: The pid of a task never changes after initialization, so reading this field is |
| // not a data race. |
| unsafe { *ptr::addr_of!((*self.as_ptr()).pid) } |
| } |
| |
| /// Returns the UID of the given task. |
| pub fn uid(&self) -> Kuid { |
| // SAFETY: It's always safe to call `task_uid` on a valid task. |
| Kuid::from_raw(unsafe { bindings::task_uid(self.as_ptr()) }) |
| } |
| |
| /// Returns the effective UID of the given task. |
| pub fn euid(&self) -> Kuid { |
| // SAFETY: It's always safe to call `task_euid` on a valid task. |
| Kuid::from_raw(unsafe { bindings::task_euid(self.as_ptr()) }) |
| } |
| |
| /// Determines whether the given task has pending signals. |
| pub fn signal_pending(&self) -> bool { |
| // SAFETY: It's always safe to call `signal_pending` on a valid task. |
| unsafe { bindings::signal_pending(self.as_ptr()) != 0 } |
| } |
| |
| /// Returns task's pid namespace with elevated reference count |
| pub fn get_pid_ns(&self) -> Option<ARef<PidNamespace>> { |
| // SAFETY: By the type invariant, we know that `self.0` is valid. |
| let ptr = unsafe { bindings::task_get_pid_ns(self.as_ptr()) }; |
| if ptr.is_null() { |
| None |
| } else { |
| // SAFETY: `ptr` is valid by the safety requirements of this function. And we own a |
| // reference count via `task_get_pid_ns()`. |
| // CAST: `Self` is a `repr(transparent)` wrapper around `bindings::pid_namespace`. |
| Some(unsafe { ARef::from_raw(ptr::NonNull::new_unchecked(ptr.cast::<PidNamespace>())) }) |
| } |
| } |
| |
| /// Returns the given task's pid in the provided pid namespace. |
| #[doc(alias = "task_tgid_nr_ns")] |
| pub fn tgid_nr_ns(&self, pidns: Option<&PidNamespace>) -> Pid { |
| let pidns = match pidns { |
| Some(pidns) => pidns.as_ptr(), |
| None => core::ptr::null_mut(), |
| }; |
| // SAFETY: By the type invariant, we know that `self.0` is valid. We received a valid |
| // PidNamespace that we can use as a pointer or we received an empty PidNamespace and |
| // thus pass a null pointer. The underlying C function is safe to be used with NULL |
| // pointers. |
| unsafe { bindings::task_tgid_nr_ns(self.as_ptr(), pidns) } |
| } |
| |
| /// Wakes up the task. |
| pub fn wake_up(&self) { |
| // SAFETY: It's always safe to call `wake_up_process` on a valid task, even if the task |
| // running. |
| unsafe { bindings::wake_up_process(self.as_ptr()) }; |
| } |
| } |
| |
| // SAFETY: The type invariants guarantee that `Task` is always refcounted. |
| unsafe impl crate::types::AlwaysRefCounted for Task { |
| fn inc_ref(&self) { |
| // SAFETY: The existence of a shared reference means that the refcount is nonzero. |
| unsafe { bindings::get_task_struct(self.as_ptr()) }; |
| } |
| |
| unsafe fn dec_ref(obj: ptr::NonNull<Self>) { |
| // SAFETY: The safety requirements guarantee that the refcount is nonzero. |
| unsafe { bindings::put_task_struct(obj.cast().as_ptr()) } |
| } |
| } |
| |
| impl Kuid { |
| /// Get the current euid. |
| #[inline] |
| pub fn current_euid() -> Kuid { |
| // SAFETY: Just an FFI call. |
| Self::from_raw(unsafe { bindings::current_euid() }) |
| } |
| |
| /// Create a `Kuid` given the raw C type. |
| #[inline] |
| pub fn from_raw(kuid: bindings::kuid_t) -> Self { |
| Self { kuid } |
| } |
| |
| /// Turn this kuid into the raw C type. |
| #[inline] |
| pub fn into_raw(self) -> bindings::kuid_t { |
| self.kuid |
| } |
| |
| /// Converts this kernel UID into a userspace UID. |
| /// |
| /// Uses the namespace of the current task. |
| #[inline] |
| pub fn into_uid_in_current_ns(self) -> bindings::uid_t { |
| // SAFETY: Just an FFI call. |
| unsafe { bindings::from_kuid(bindings::current_user_ns(), self.kuid) } |
| } |
| } |
| |
| impl PartialEq for Kuid { |
| #[inline] |
| fn eq(&self, other: &Kuid) -> bool { |
| // SAFETY: Just an FFI call. |
| unsafe { bindings::uid_eq(self.kuid, other.kuid) } |
| } |
| } |
| |
| impl Eq for Kuid {} |