// SPDX-License-Identifier: GPL-2.0 // Copyright (C) 2024 Google LLC. //! Credentials management.//!//! C header: [`include/linux/cred.h`](srctree/include/linux/cred.h).//!//! Reference: <https://www.kernel.org/doc/html/latest/security/credentials.html> use crate::{bindings, sync::aref::AlwaysRefCounted, task::Kuid, types::Opaque}; /// Wraps the kernel's `struct cred`.////// Credentials are used for various security checks in the kernel.////// Most fields of credentials are immutable. When things have their credentials changed, that/// happens by replacing the credential instead of changing an existing credential. See the [kernel/// documentation][ref] for more info on this.////// # Invariants////// Instances of this type are always ref-counted, that is, a call to `get_cred` ensures that the/// allocation remains valid at least until the matching call to `put_cred`.////// [ref]: https://www.kernel.org/doc/html/latest/security/credentials.html#[repr(transparent)]pub struct Credential(Opaque<bindings::cred>); // SAFETY:// - `Credential::dec_ref` can be called from any thread.// - It is okay to send ownership of `Credential` across thread boundaries.unsafe impl Send for Credential {} // SAFETY: It's OK to access `Credential` through shared references from other threads because// we're either accessing properties that don't change or that are properly synchronised by C code.unsafe impl Sync for Credential {} impl Credential {    /// Creates a reference to a [`Credential`] from a valid pointer.    ///    /// # Safety    ///    /// The caller must ensure that `ptr` is valid and remains valid for the lifetime of the    /// returned [`Credential`] reference.    #[inline]    pub unsafe fn from_ptr<'a>(ptr: *const bindings::cred) -> &'a Credential {        // SAFETY: The safety requirements guarantee the validity of the dereference, while the        // `Credential` type being transparent makes the cast ok.        unsafe { &*ptr.cast() }    }     /// Returns a raw pointer to the inner credential.    #[inline]    pub fn as_ptr(&self) -> *const bindings::cred {        self.0.get()    }     /// Get the id for this security context.    #[inline]    pub fn get_secid(&self) -> u32 {        let mut secid = 0;        // SAFETY: The invariants of this type ensures that the pointer is valid.        unsafe { bindings::security_cred_getsecid(self.0.get(), &mut secid) };        secid    }     /// Returns the effective UID of the given credential.    #[inline]    pub fn euid(&self) -> Kuid {        // SAFETY: By the type invariant, we know that `self.0` is valid. Furthermore, the `euid`        // field of a credential is never changed after initialization, so there is no potential        // for data races.        Kuid::from_raw(unsafe { (*self.0.get()).euid })    }} // SAFETY: The type invariants guarantee that `Credential` is always ref-counted.unsafe impl AlwaysRefCounted for Credential {    #[inline]    fn inc_ref(&self) {        // SAFETY: The existence of a shared reference means that the refcount is nonzero.        unsafe { bindings::get_cred(self.0.get()) };    }     #[inline]    unsafe fn dec_ref(obj: core::ptr::NonNull<Credential>) {        // SAFETY: The safety requirements guarantee that the refcount is nonzero. The cast is okay        // because `Credential` has the same representation as `struct cred`.        unsafe { bindings::put_cred(obj.cast().as_ptr()) };    }}