From: Wedson Almeida Filho <[email protected]>
Make it possible to access credentials from Rust drivers. In particular,
this patch makes it possible to get the id for the security context of a
given file.
Signed-off-by: Wedson Almeida Filho <[email protected]>
Co-Developed-by: Alice Ryhl <[email protected]>
Signed-off-by: Alice Ryhl <[email protected]>
---
rust/bindings/bindings_helper.h | 2 +
rust/helpers.c | 22 +++++++++++
rust/kernel/cred.rs | 66 +++++++++++++++++++++++++++++++++
rust/kernel/file.rs | 15 ++++++++
rust/kernel/lib.rs | 1 +
5 files changed, 106 insertions(+)
create mode 100644 rust/kernel/cred.rs
diff --git a/rust/kernel/cred.rs b/rust/kernel/cred.rs
new file mode 100644
index 000000000000..ca3fac4851a2
--- /dev/null
+++ b/rust/kernel/cred.rs
@@ -0,0 +1,66 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! Credentials management.
+//!
+//! C header: [`include/linux/cred.h`](../../../../include/linux/cred.h)
+//!
+//! Reference: <https://www.kernel.org/doc/html/latest/security/credentials.html>
+
+use crate::{
+ bindings,
+ types::{AlwaysRefCounted, Opaque},
+};
+
+/// Wraps the kernel's `struct cred`.
+///
+/// # 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`.
+#[repr(transparent)]
+pub struct Credential(pub(crate) Opaque<bindings::cred>);
+
+// SAFETY: By design, the only way to access a `Credential` is via an immutable reference or an
+// `ARef`. This means that the only situation in which a `Credential` 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 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.
+ 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() }
+ }
+
+ /// Get the id for this security context.
+ 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
+ }
+}
+
+// SAFETY: The type invariants guarantee that `Credential` is always ref-counted.
+unsafe impl AlwaysRefCounted for Credential {
+ fn inc_ref(&self) {
+ // SAFETY: The existence of a shared reference means that the refcount is nonzero.
+ unsafe { bindings::get_cred(self.0.get()) };
+ }
+
+ unsafe fn dec_ref(obj: core::ptr::NonNull<Self>) {
+ // SAFETY: The safety requirements guarantee that the refcount is nonzero.
+ unsafe { bindings::put_cred(obj.cast().as_ptr()) };
+ }
+}
diff --git a/rust/kernel/file.rs b/rust/kernel/file.rs
index 99657adf2472..d379ae2906d9 100644
--- a/rust/kernel/file.rs
+++ b/rust/kernel/file.rs
@@ -7,6 +7,7 @@
use crate::{
bindings,
+ cred::Credential,
error::{code::*, Error, Result},
types::{ARef, AlwaysRefCounted, Opaque},
};
@@ -138,6 +139,20 @@ pub unsafe fn from_ptr<'a>(ptr: *const bindings::file) -> &'a File {
unsafe { &*ptr.cast() }
}
+ /// Returns the credentials of the task that originally opened the file.
+ pub fn cred(&self) -> &Credential {
+ // SAFETY: The file is valid because the shared reference guarantees a nonzero refcount.
+ //
+ // This uses a volatile read because C code may be modifying this field in parallel using
+ // non-atomic unsynchronized writes. This corresponds to how the C macro READ_ONCE is
+ // implemented.
+ let ptr = unsafe { core::ptr::addr_of!((*self.0.get()).f_cred).read_volatile() };
+ // SAFETY: The lifetimes of `self` and `Credential` are tied, so it is guaranteed that
+ // the credential pointer remains valid (because the file is still alive, and it doesn't
+ // change over the lifetime of a file).
+ unsafe { Credential::from_ptr(ptr) }
+ }
+
/// Returns the flags associated with the file.
///
/// The flags are a combination of the constants in [`flags`].
diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs
index 650bfffc1e6f..07258bfa8960 100644
--- a/rust/kernel/lib.rs
+++ b/rust/kernel/lib.rs
@@ -31,6 +31,7 @@
#[cfg(not(testlib))]
mod allocator;
mod build_assert;
+pub mod cred;
pub mod error;
pub mod file;
pub mod init;
diff --git a/rust/bindings/bindings_helper.h b/rust/bindings/bindings_helper.h
index c5b2cfd02bac..d89f0df93615 100644
--- a/rust/bindings/bindings_helper.h
+++ b/rust/bindings/bindings_helper.h
@@ -6,9 +6,11 @@
* Sorted alphabetically.
*/
+#include <linux/cred.h>
#include <linux/errname.h>
#include <linux/file.h>
#include <linux/fs.h>
+#include <linux/security.h>
#include <linux/slab.h>
#include <linux/refcount.h>
#include <linux/wait.h>
diff --git a/rust/helpers.c b/rust/helpers.c
index 072f7ef80ea5..e13a7da430b1 100644
--- a/rust/helpers.c
+++ b/rust/helpers.c
@@ -22,12 +22,14 @@
#include <linux/bug.h>
#include <linux/build_bug.h>
+#include <linux/cred.h>
#include <linux/err.h>
#include <linux/errname.h>
#include <linux/fs.h>
#include <linux/mutex.h>
#include <linux/refcount.h>
#include <linux/sched/signal.h>
+#include <linux/security.h>
#include <linux/spinlock.h>
#include <linux/wait.h>
@@ -144,6 +146,26 @@ struct file *rust_helper_get_file(struct file *f)
}
EXPORT_SYMBOL_GPL(rust_helper_get_file);
+const struct cred *rust_helper_get_cred(const struct cred *cred)
+{
+ return get_cred(cred);
+}
+EXPORT_SYMBOL_GPL(rust_helper_get_cred);
+
+void rust_helper_put_cred(const struct cred *cred)
+{
+ put_cred(cred);
+}
+EXPORT_SYMBOL_GPL(rust_helper_put_cred);
+
+#ifndef CONFIG_SECURITY
+void rust_helper_security_cred_getsecid(const struct cred *c, u32 *secid)
+{
+ security_cred_getsecid(c, secid);
+}
+EXPORT_SYMBOL_GPL(rust_helper_security_cred_getsecid);
+#endif
+
/*
* We use `bindgen`'s `--size_t-is-usize` option to bind the C `size_t` type
* as the Rust `usize` type, so we can use it in contexts where Rust
--
2.41.0.255.g8b1d071c50-goog