1 files changed, 74 insertions, 0 deletions
diff --git a/rust/kernel/security.rs b/rust/kernel/security.rs
new file mode 100644
index 000000000000..0c63e9e7e564
--- /dev/null
+++ b/rust/kernel/security.rs
@@ -0,0 +1,74 @@
+// SPDX-License-Identifier: GPL-2.0
+
+// Copyright (C) 2024 Google LLC.
+
+//! Linux Security Modules (LSM).
+//!
+//! C header: [`include/linux/security.h`](srctree/include/linux/security.h).
+
+use crate::{
+    bindings,
+    error::{to_result, Result},
+};
+
+/// A security context string.
+///
+/// # Invariants
+///
+/// The `ctx` field corresponds to a valid security context as returned by a successful call to
+/// `security_secid_to_secctx`, that has not yet been released by `security_release_secctx`.
+pub struct SecurityCtx {
+    ctx: bindings::lsm_context,
+}
+
+impl SecurityCtx {
+    /// Get the security context given its id.
+    #[inline]
+    pub fn from_secid(secid: u32) -> Result<Self> {
+        // SAFETY: `struct lsm_context` can be initialized to all zeros.
+        let mut ctx: bindings::lsm_context = unsafe { core::mem::zeroed() };
+
+        // SAFETY: Just a C FFI call. The pointer is valid for writes.
+        to_result(unsafe { bindings::security_secid_to_secctx(secid, &mut ctx) })?;
+
+        // INVARIANT: If the above call did not fail, then we have a valid security context.
+        Ok(Self { ctx })
+    }
+
+    /// Returns whether the security context is empty.
+    #[inline]
+    pub fn is_empty(&self) -> bool {
+        self.ctx.len == 0
+    }
+
+    /// Returns the length of this security context.
+    #[inline]
+    pub fn len(&self) -> usize {
+        self.ctx.len as usize
+    }
+
+    /// Returns the bytes for this security context.
+    #[inline]
+    pub fn as_bytes(&self) -> &[u8] {
+        let ptr = self.ctx.context;
+        if ptr.is_null() {
+            debug_assert_eq!(self.len(), 0);
+            // We can't pass a null pointer to `slice::from_raw_parts` even if the length is zero.
+            return &[];
+        }
+
+        // SAFETY: The call to `security_secid_to_secctx` guarantees that the pointer is valid for
+        // `self.len()` bytes. Furthermore, if the length is zero, then we have ensured that the
+        // pointer is not null.
+        unsafe { core::slice::from_raw_parts(ptr.cast(), self.len()) }
+    }
+}
+
+impl Drop for SecurityCtx {
+    #[inline]
+    fn drop(&mut self) {
+        // SAFETY: By the invariant of `Self`, this releases an lsm context that came from a
+        // successful call to `security_secid_to_secctx` and has not yet been released.
+        unsafe { bindings::security_release_secctx(&mut self.ctx) };
+    }
+}