[PATCH v10 5/8] rust: security: add abstraction for secctx

[Kees Cook]

On Sun, Sep 15, 2024 at 02:31:31PM +0000, Alice Ryhl wrote:
> Add an abstraction for viewing the string representation of a security
> context.

Hm, this may collide with "LSM: Move away from secids" is going to happen.
https://lore.kernel.org/all/20240830003411.16818-1-casey@schaufler-ca.com/

This series is not yet landed, but in the future, the API changes should
be something like this, though the "lsmblob" name is likely to change to
"lsmprop"?
security_cred_getsecid()   -> security_cred_getlsmblob()
security_secid_to_secctx() -> security_lsmblob_to_secctx()

> This is needed by Rust Binder because it has a feature where a process
> can view the string representation of the security context for incoming
> transactions. The process can use that to authenticate incoming
> transactions, and since the feature is provided by the kernel, the
> process can trust that the security context is legitimate.
> 
> This abstraction makes the following assumptions about the C side:
> * When a call to `security_secid_to_secctx` is successful, it returns a
>   pointer and length. The pointer references a byte string and is valid
>   for reading for that many bytes.

Yes. (len includes trailing C-String NUL character.)

> * The string may be referenced until `security_release_secctx` is
>   called.

Yes.

> * If CONFIG_SECURITY is set, then the three methods mentioned in
>   rust/helpers are available without a helper. (That is, they are not a
>   #define or `static inline`.)

Yes.

> 
> Reviewed-by: Benno Lossin <benno.lossin at proton.me>
> Reviewed-by: Martin Rodriguez Reboredo <yakoyoku at gmail.com>
> Reviewed-by: Trevor Gross <tmgross at umich.edu>
> Reviewed-by: Gary Guo <gary at garyguo.net>
> Signed-off-by: Alice Ryhl <aliceryhl at google.com>

Reviewed-by: Kees Cook <kees at kernel.org>

-- 
Kees Cook