linux-kernel - Re: [PATCH v5 4/8] LSM: lsm_get_self_attr syscall for LSM self attributes

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Message-Id: <f8dca9d2-6e5e-4584-88b3-f71f62988dab@app.fastmail.com>
Date:   Thu, 12 Jan 2023 15:40:00 +0100
From:   "Arnd Bergmann" <arnd@...db.de>
To:     "Casey Schaufler" <casey@...aufler-ca.com>,
        casey.schaufler@...el.com, "Paul Moore" <paul@...l-moore.com>,
        linux-security-module@...r.kernel.org
Cc:     jmorris@...ei.org, "Kees Cook" <keescook@...omium.org>,
        john.johansen@...onical.com,
        "Tetsuo Handa" <penguin-kernel@...ove.sakura.ne.jp>,
        stephen.smalley.work@...il.com, linux-kernel@...r.kernel.org,
        linux-api@...r.kernel.org, mic@...ikod.net
Subject: Re: [PATCH v5 4/8] LSM: lsm_get_self_attr syscall for LSM self attributes

On Mon, Jan 9, 2023, at 19:07, Casey Schaufler wrote:
> +/**
> + * struct lsm_ctx - LSM context
> + * @id: the LSM id number, see LSM_ID_XXX
> + * @flags: context specifier and LSM specific flags
> + * @ctx_len: the size of @ctx
> + * @ctx: the LSM context, a nul terminated string
> + *
> + * @ctx in a nul terminated string.
> + *	(strlen(@ctx) < @ctx_len) is always true.
> + *	(strlen(@ctx) == @ctx_len + 1) is not guaranteed.
> + */
> +struct lsm_ctx {
> +	__u32		id;
> +	__u64		flags;
> +	__kernel_size_t	ctx_len;
> +	__u8		ctx[];
> +};

I think this should be changed to be the same layout on
all architectures regardless of __u64 alignment and
sizeof(__kernel_size_t) differences, to avoid the need
for compat syscalls and explicit clearing of the
internal padding.

Maybe just use __u64 fields for all three integers?

     Arnd