[RFC] Obtaining PATH entry without audit userland

[Steve Grubb]

On Thursday 10 January 2008 03:42:38 Yuichi Nakamura wrote:
> Hi.
>
> When debugging SELinux policy, PATH audit entry is useful.
> In current audit,
> context->dummy should be 0 to obtain PATH entry,
> but it is set 1 if no audit rules are registered,
> so some audit rule should be registered to obtain PATH entry.
>
> To register audit rule, we need audit userland.
> However, in embedded devices
> we want as little userland as possible,
> because hardware resource is constrained and cross-compiling is tiresome.
>
> We want PATH entry to debug SELinux policy,
> we do not want to port audit userland for this purpose,
> so we want to do it in kernel.
>
> Following is simple patch to obtain PATH entry without audit userland.
> Does this sound reasonable??

I was under the impression that Al Viro has already sent a patch allowing for 
PATH in all AVC messages. Al?


> Signed-off-by: Yuichi Nakamura<ynakam at hitachisoft.jp>
> ---
>  init/Kconfig     |   10 ++++++++++
>  kernel/audit.h   |    7 +++++++
>  kernel/auditsc.c |    9 ++++++++-
>  3 files changed, 25 insertions(+), 1 deletion(-)
> diff -purN -X linux-2.6.22.1/Documentation/dontdiff
> linux-2.6.22.1.old/kernel/audit.h linux-2.6.22.1/kernel/audit.h ---
> linux-2.6.22.1.old/kernel/audit.h	2007-12-19 10:00:19.000000000 +0900 +++
> linux-2.6.22.1/kernel/audit.h	2008-01-09 09:04:28.000000000 +0900 @@ -143,6
> +143,13 @@ static inline int audit_signal_info(int
>  extern enum audit_state audit_filter_inodes(struct task_struct *,
>  					    struct audit_context *);
>  extern void audit_set_auditable(struct audit_context *);
> +
> +#ifdef CONFIG_AUDIT_PATH
> +#define DEFAULT_AUDIT_PATH_ENTRY 1
> +#else
> +#define DEFAULT_AUDIT_PATH_ENTRY 0
> +#endif
> +
>  #else
>  #define audit_signal_info(s,t) AUDIT_DISABLED
>  #define audit_filter_inodes(t,c) AUDIT_DISABLED
> diff -purN -X linux-2.6.22.1/Documentation/dontdiff
> linux-2.6.22.1.old/kernel/auditsc.c linux-2.6.22.1/kernel/auditsc.c ---
> linux-2.6.22.1.old/kernel/auditsc.c	2007-12-19 10:00:19.000000000 +0900 +++
> linux-2.6.22.1/kernel/auditsc.c	2008-01-09 08:57:44.000000000 +0900 @@
> -227,6 +227,8 @@ struct audit_context {
>  #endif
>  };
>
> +int audit_path_entry = DEFAULT_AUDIT_PATH_ENTRY;
> +
>  #define ACC_MODE(x) ("\004\002\006\006"[(x)&O_ACCMODE])
>  static inline int open_arg(int flags, int mask)
>  {
> @@ -1198,7 +1200,12 @@ void audit_syscall_entry(int arch, int m
>  	context->argv[3]    = a4;
>
>  	state = context->state;
> -	context->dummy = !audit_n_rules;
> +
> +	if (audit_path_entry)
> +		context->dummy = 0;
> +	else
> +		context->dummy = !audit_n_rules;
> +
>  	if (!context->dummy && (state == AUDIT_SETUP_CONTEXT || state ==
> AUDIT_BUILD_CONTEXT)) state = audit_filter_syscall(tsk, context,
> &audit_filter_list[AUDIT_FILTER_ENTRY]); if (likely(state ==
> AUDIT_DISABLED))
> --- linux-2.6.22.1.old/init/Kconfig	2008-01-08 13:49:30.000000000 +0900
> +++ linux-2.6.22.1/init/Kconfig	2007-12-19 11:50:17.000000000 +0900
> @@ -245,6 +245,16 @@ config AUDITSYSCALL
>  	  such as SELinux.  To use audit's filesystem watch feature, please
>  	  ensure that INOTIFY is configured.
>
> +config AUDIT_PATH
> +	bool "Audit always PATH entry"
> +	depends on AUDITSYSCALL
> +	default n
> +	help
> +	  By default, PATH entry is not audited unless
> +          you register some audit rule.
> +	  With this option, PATH entry is always audited.
> +	  This is useful in debugging SELinux policy without audit userland.
> +
>  config IKCONFIG
>  	tristate "Kernel .config support"
>  	---help---