Merge tag 'vfs-6.13.rust.file' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs

Pull vfs rust file abstractions from Christian Brauner:
 "This contains the file abstractions needed by the Rust implementation
  of the Binder driver and other parts of the kernel.

  Let's treat this as a first attempt at getting something working but I
  do expect the actual interfaces to change significantly over time.
  Simply because we are still figuring out what actually works. But
  there's no point in further theorizing. Let's see how it holds up with
  actual users"

* tag 'vfs-6.13.rust.file' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs:
  rust: task: adjust safety comments in Task methods
  rust: add seqfile abstraction
  rust: file: add abstraction for `poll_table`
  rust: file: add `Kuid` wrapper
  rust: file: add `FileDescriptorReservation`
  rust: security: add abstraction for secctx
  rust: cred: add Rust abstraction for `struct cred`
  rust: file: add Rust abstraction for `struct file`
  rust: task: add `Task::current_raw`
  rust: types: add `NotThreadSafe`

1 files changed, 100 insertions, 20 deletions

diff --git a/rust/kernel/task.rs b/rust/kernel/task.rs
index 55dff7e088bf..080599075875 100644
--- a/rust/kernel/task.rs
+++ b/rust/kernel/task.rs
@@ -4,10 +4,13 @@
 //!
 //! C header: [`include/linux/sched.h`](srctree/include/linux/sched.h).
 
-use crate::types::Opaque;
+use crate::{
+    bindings,
+    types::{NotThreadSafe, Opaque},
+};
 use core::{
+    cmp::{Eq, PartialEq},
     ffi::{c_int, c_long, c_uint},
-    marker::PhantomData,
     ops::Deref,
     ptr,
 };
@@ -94,7 +97,22 @@ unsafe impl Sync for Task {}
 /// The type of process identifiers (PIDs).
 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
@@ -106,7 +124,7 @@ impl Task {
     pub unsafe fn current() -> impl Deref<Target = Task> {
         struct TaskRef<'a> {
             task: &'a Task,
-            _not_send: PhantomData<*mut ()>,
+            _not_send: NotThreadSafe,
         }
 
         impl Deref for TaskRef<'_> {
@@ -117,23 +135,27 @@ impl Task {
             }
         }
 
-        // SAFETY: Just an FFI call with no additional safety requirements.
-        let ptr = unsafe { bindings::get_current() };
-
+        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 { &*ptr.cast() },
-            _not_send: PhantomData,
+            task: unsafe { &*current.cast() },
+            _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: By the type invariant, we know that `self.0` is a valid task. Valid tasks always
-        // have a valid `group_leader`.
-        let ptr = unsafe { *ptr::addr_of!((*self.0.get()).group_leader) };
+        // 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
@@ -143,23 +165,41 @@ impl Task {
 
     /// Returns the PID of the given task.
     pub fn pid(&self) -> Pid {
-        // SAFETY: By the type invariant, we know that `self.0` is a valid task. Valid tasks always
-        // have a valid pid.
-        unsafe { *ptr::addr_of!((*self.0.get()).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: By the type invariant, we know that `self.0` is valid.
-        unsafe { bindings::signal_pending(self.0.get()) != 0 }
+        // SAFETY: It's always safe to call `signal_pending` on a valid task.
+        unsafe { bindings::signal_pending(self.as_ptr()) != 0 }
+    }
+
+    /// Returns the given task's pid in the current pid namespace.
+    pub fn pid_in_current_ns(&self) -> Pid {
+        // SAFETY: It's valid to pass a null pointer as the namespace (defaults to current
+        // namespace). The task pointer is also valid.
+        unsafe { bindings::task_tgid_nr_ns(self.as_ptr(), ptr::null_mut()) }
     }
 
     /// Wakes up the task.
     pub fn wake_up(&self) {
-        // SAFETY: By the type invariant, we know that `self.0.get()` is non-null and valid.
-        // And `wake_up_process` is safe to be called for any valid task, even if the task is
+        // SAFETY: It's always safe to call `signal_pending` on a valid task, even if the task
         // running.
-        unsafe { bindings::wake_up_process(self.0.get()) };
+        unsafe { bindings::wake_up_process(self.as_ptr()) };
     }
 }
 
@@ -167,7 +207,7 @@ impl Task {
 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.0.get()) };
+        unsafe { bindings::get_task_struct(self.as_ptr()) };
     }
 
     unsafe fn dec_ref(obj: ptr::NonNull<Self>) {
@@ -175,3 +215,43 @@ unsafe impl crate::types::AlwaysRefCounted for Task {
         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 {}