linux-kernel - Re: [PATCH bpf-next v2 04/10] bpf: lsm: Add mutable hooks list for the BPF LSM

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Date:   Wed, 15 Jan 2020 12:30:08 -0500
From:   Stephen Smalley <sds@...ho.nsa.gov>
To:     KP Singh <kpsingh@...omium.org>, linux-kernel@...r.kernel.org,
        bpf@...r.kernel.org, linux-security-module@...r.kernel.org
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        James Morris <jmorris@...ei.org>,
        Kees Cook <keescook@...omium.org>,
        Thomas Garnier <thgarnie@...omium.org>,
        Michael Halcrow <mhalcrow@...gle.com>,
        Paul Turner <pjt@...gle.com>,
        Brendan Gregg <brendan.d.gregg@...il.com>,
        Jann Horn <jannh@...gle.com>,
        Matthew Garrett <mjg59@...gle.com>,
        Christian Brauner <christian@...uner.io>,
        Mickaël Salaün <mic@...ikod.net>,
        Florent Revest <revest@...omium.org>,
        Brendan Jackman <jackmanb@...omium.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        "Serge E. Hallyn" <serge@...lyn.com>,
        Mauro Carvalho Chehab <mchehab+samsung@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Nicolas Ferre <nicolas.ferre@...rochip.com>,
        Stanislav Fomichev <sdf@...gle.com>,
        Quentin Monnet <quentin.monnet@...ronome.com>,
        Andrey Ignatov <rdna@...com>, Joe Stringer <joe@...d.net.nz>
Subject: Re: [PATCH bpf-next v2 04/10] bpf: lsm: Add mutable hooks list for
 the BPF LSM

On 1/15/20 12:13 PM, KP Singh wrote:
> From: KP Singh <kpsingh@...gle.com>
> 
> - The list of hooks registered by an LSM is currently immutable as they
>    are declared with __lsm_ro_after_init and they are attached to a
>    security_hook_heads struct.
> - For the BPF LSM we need to de/register the hooks at runtime. Making
>    the existing security_hook_heads mutable broadens an
>    attack vector, so a separate security_hook_heads is added for only
>    those that ~must~ be mutable.
> - These mutable hooks are run only after all the static hooks have
>    successfully executed.
> 
> This is based on the ideas discussed in:
> 
>    https://lore.kernel.org/lkml/20180408065916.GA2832@ircssh-2.c.rugged-nimbus-611.internal
> 
> Signed-off-by: KP Singh <kpsingh@...gle.com>
> ---
[...]
> diff --git a/security/security.c b/security/security.c
> index cd2d18d2d279..4a2eb4c089b2 100644
> --- a/security/security.c
> +++ b/security/security.c
> @@ -652,20 +653,21 @@ static void __init lsm_early_task(struct task_struct *task)
>   								\
>   		hlist_for_each_entry(P, &security_hook_heads.FUNC, list) \
>   			P->hook.FUNC(__VA_ARGS__);		\
> +		CALL_BPF_LSM_VOID_HOOKS(FUNC, __VA_ARGS__);	\
>   	} while (0)
>   
> -#define call_int_hook(FUNC, IRC, ...) ({			\
> -	int RC = IRC;						\
> -	do {							\
> -		struct security_hook_list *P;			\
> -								\
> +#define call_int_hook(FUNC, IRC, ...) ({				\
> +	int RC = IRC;							\
> +	do {								\
> +		struct security_hook_list *P;				\
>   		hlist_for_each_entry(P, &security_hook_heads.FUNC, list) { \
> -			RC = P->hook.FUNC(__VA_ARGS__);		\
> -			if (RC != 0)				\
> -				break;				\
> -		}						\
> -	} while (0);						\
> -	RC;							\
> +			RC = P->hook.FUNC(__VA_ARGS__);			\
> +			if (RC != 0)					\
> +				break;					\
> +		}							\
> +		RC = CALL_BPF_LSM_INT_HOOKS(RC, FUNC, __VA_ARGS__);	\

Let's not clobber the return code from the other LSMs with the bpf one.

> +	} while (0);							\
> +	RC;								\
>   })
>   
>   /* Security operations */
>