linux-kernel - Re: [PATCH 04/13] Audit: maintain an lsmblob in audit

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Message-ID: <a8aeacdc4afec5855fa4b80f0f5f43e8f7d3b5cb.camel@canonical.com>
Date: Tue, 27 Aug 2024 12:01:58 -0300
From: Georgia Garcia <georgia.garcia@...onical.com>
To: Casey Schaufler <casey@...aufler-ca.com>, paul@...l-moore.com, 
	linux-security-module@...r.kernel.org
Cc: jmorris@...ei.org, serge@...lyn.com, keescook@...omium.org, 
 john.johansen@...onical.com, penguin-kernel@...ove.sakura.ne.jp, 
 stephen.smalley.work@...il.com, linux-kernel@...r.kernel.org,
 mic@...ikod.net
Subject: Re: [PATCH 04/13] Audit: maintain an lsmblob in audit_context

On Sun, 2024-08-25 at 12:00 -0700, Casey Schaufler wrote:
> Replace the secid value stored in struct audit_context with a struct
> lsmblob. Change the code that uses this value to accommodate the
> change. security_audit_rule_match() expects a lsmblob, so existing
> scaffolding can be removed. A call to security_secid_to_secctx()
> is changed to security_lsmblob_to_secctx().  The call to
> security_ipc_getsecid() is scaffolded.
> 
> A new function lsmblob_is_set() is introduced to identify whether
> an lsmblob contains a non-zero value.
> 
> Signed-off-by: Casey Schaufler <casey@...aufler-ca.com>
> ---
>  include/linux/security.h | 13 +++++++++++++
>  kernel/audit.h           |  3 ++-
>  kernel/auditsc.c         | 19 ++++++++-----------
>  3 files changed, 23 insertions(+), 12 deletions(-)
> 
> diff --git a/include/linux/security.h b/include/linux/security.h
> index 457fafc32fb0..a0b23b6e8734 100644
> --- a/include/linux/security.h
> +++ b/include/linux/security.h
> @@ -277,6 +277,19 @@ static inline const char *kernel_load_data_id_str(enum kernel_load_data_id id)
>  	return kernel_load_data_str[id];
>  }
>  
> +/**
> + * lsmblob_is_set - report if there is a value in the lsmblob
> + * @blob: Pointer to the exported LSM data
> + *
> + * Returns true if there is a value set, false otherwise
> + */
> +static inline bool lsmblob_is_set(struct lsmblob *blob)
> +{
> +	const struct lsmblob empty = {};
> +
> +	return !!memcmp(blob, &empty, sizeof(*blob));
> +}
> +
>  #ifdef CONFIG_SECURITY
>  
>  int call_blocking_lsm_notifier(enum lsm_event event, void *data);
> diff --git a/kernel/audit.h b/kernel/audit.h
> index a60d2840559e..b1f2de4d4f1e 100644
> --- a/kernel/audit.h
> +++ b/kernel/audit.h
> @@ -11,6 +11,7 @@
>  
>  #include <linux/fs.h>
>  #include <linux/audit.h>
> +#include <linux/security.h>
>  #include <linux/skbuff.h>
>  #include <uapi/linux/mqueue.h>
>  #include <linux/tty.h>
> @@ -160,7 +161,7 @@ struct audit_context {
>  			kuid_t			uid;
>  			kgid_t			gid;
>  			umode_t			mode;
> -			u32			osid;
> +			struct lsmblob		oblob;
>  			int			has_perm;
>  			uid_t			perm_uid;
>  			gid_t			perm_gid;
> diff --git a/kernel/auditsc.c b/kernel/auditsc.c
> index 23adb15cae43..84f6e9356b8f 100644
> --- a/kernel/auditsc.c
> +++ b/kernel/auditsc.c
> @@ -724,9 +724,7 @@ static int audit_filter_rules(struct task_struct *tsk,
>  				/* Find ipc objects that match */
>  				if (!ctx || ctx->type != AUDIT_IPC)
>  					break;
> -				/* scaffolding */
> -				blob.scaffold.secid = ctx->ipc.osid;
> -				if (security_audit_rule_match(&blob,
> +				if (security_audit_rule_match(&ctx->ipc.oblob,
>  							      f->type, f->op,
>  							      f->lsm_rule))
>  					++result;
> @@ -1394,19 +1392,17 @@ static void show_special(struct audit_context *context, int *call_panic)
>  			audit_log_format(ab, " a%d=%lx", i,
>  				context->socketcall.args[i]);
>  		break; }
> -	case AUDIT_IPC: {
> -		u32 osid = context->ipc.osid;
> -
> +	case AUDIT_IPC:
>  		audit_log_format(ab, "ouid=%u ogid=%u mode=%#ho",
>  				 from_kuid(&init_user_ns, context->ipc.uid),
>  				 from_kgid(&init_user_ns, context->ipc.gid),
>  				 context->ipc.mode);
> -		if (osid) {
> +		if (lsmblob_is_set(&context->ipc.oblob)) {
>  			char *ctx = NULL;
>  			u32 len;
>  
> -			if (security_secid_to_secctx(osid, &ctx, &len)) {
> -				audit_log_format(ab, " osid=%u", osid);
> +			if (security_lsmblob_to_secctx(&context->ipc.oblob,
> +						       &ctx, &len)) {

Is there any reason to stop auditing secid when we fail to get the
security context?

>  				*call_panic = 1;
>  			} else {
>  				audit_log_format(ab, " obj=%s", ctx);
> @@ -1426,7 +1422,7 @@ static void show_special(struct audit_context *context, int *call_panic)
>  				context->ipc.perm_gid,
>  				context->ipc.perm_mode);
>  		}
> -		break; }
> +		break;
>  	case AUDIT_MQ_OPEN:
>  		audit_log_format(ab,
>  			"oflag=0x%x mode=%#ho mq_flags=0x%lx mq_maxmsg=%ld "
> @@ -2642,7 +2638,8 @@ void __audit_ipc_obj(struct kern_ipc_perm *ipcp)
>  	context->ipc.gid = ipcp->gid;
>  	context->ipc.mode = ipcp->mode;
>  	context->ipc.has_perm = 0;
> -	security_ipc_getsecid(ipcp, &context->ipc.osid);
> +	/* scaffolding */
> +	security_ipc_getsecid(ipcp, &context->ipc.oblob.scaffold.secid);
>  	context->type = AUDIT_IPC;
>  }
>