Re: [PATCH] lsm: rust: mark SecurityCtx methods inline

Casey Schaufler
2025-03-03T17:17:21Z

On 3/3/2025 7:29 AM, Alice Ryhl wrote:
> I'm seeing Binder generating calls to methods on SecurityCtx such as
> from_secid and drop without inlining. Since these methods are really
> simple wrappers around C functions, mark the methods to inline to avoid
> generating these useless small functions.
>
> Signed-off-by: Alice Ryhl <aliceryhl@google.com>
> ---
> rust/kernel/security.rs | 5 +++++
> 1 file changed, 5 insertions(+)
>
> diff --git a/rust/kernel/security.rs b/rust/kernel/security.rs
> index 25d2b1ac3833..243211050526 100644
> --- a/rust/kernel/security.rs
> +++ b/rust/kernel/security.rs
> @@ -23,6 +23,7 @@ pub struct SecurityCtx {
>
> 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() };
> @@ -35,16 +36,19 @@ pub fn from_secid(secid: u32) -> Result<Self> {
> }
>
> /// 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() {
> @@ -61,6 +65,7 @@ pub fn as_bytes(&self) -> &[u8] {
> }
>
> impl Drop for SecurityCtx {
> + #[inline]
> fn drop(&mut self) {
> // SAFETY: By the invariant of `Self`, this frees a context that came from a successful
> // call to `security_secid_to_secctx` and has not yet been destroyed by

I don't speak rust (well, yet?) so I can't talk about that, but this comment
has me concerned. Security contexts (secctx) are not destroyed, they are released.
While SELinux allocates and frees them, Smack maintains a list of contexts that
is never freed. A call to security_release_secctx() on SELinux "destroys" the
secctx, but for Smack does not.

>
> ---
> base-commit: a64dcfb451e254085a7daee5fe51bf22959d52d3
> change-id: 20250303-inline-securityctx-6fc1ca669156
>
> Best regards,