Re: [PATCH] audit: allow not equal op for audit by executable

[Steve Grubb <sgrubb@redhat.com>]

On Friday, April 6, 2018 4:43:00 AM EDT Ondrej Mosnacek wrote:
> Current implementation of auditing by executable name only implements
> the 'equal' operator. This patch extends it to also support the 'not
> equal' operator.
> 
> See: https://github.com/linux-audit/audit-kernel/issues/53

What would an audit rule that uses this new capability look like?

-Steve

> Signed-off-by: Ondrej Mosnacek <omosnace@redhat.com>
> ---
> 
> Hi Paul,
> 
> this turned out to be easier than I anticipated so I'm sending the patch
> already :) I hope I got everything right. Note that the userspace tools
> also need to be updated to check the feature bit and allow/disallow the
> operator based on that.
> 
> Ondrej
> 
>  include/uapi/linux/audit.h | 18 ++++++++++--------
>  kernel/auditfilter.c       |  2 +-
>  kernel/auditsc.c           |  2 ++
>  3 files changed, 13 insertions(+), 9 deletions(-)
> 
> diff --git a/include/uapi/linux/audit.h b/include/uapi/linux/audit.h
> index 4e61a9e05132..03393f7e8932 100644
> --- a/include/uapi/linux/audit.h
> +++ b/include/uapi/linux/audit.h
> @@ -333,13 +333,14 @@ enum {
>  #define AUDIT_STATUS_BACKLOG_WAIT_TIME	0x0020
>  #define AUDIT_STATUS_LOST		0x0040
> 
> -#define AUDIT_FEATURE_BITMAP_BACKLOG_LIMIT	0x00000001
> -#define AUDIT_FEATURE_BITMAP_BACKLOG_WAIT_TIME	0x00000002
> -#define AUDIT_FEATURE_BITMAP_EXECUTABLE_PATH	0x00000004
> -#define AUDIT_FEATURE_BITMAP_EXCLUDE_EXTEND	0x00000008
> -#define AUDIT_FEATURE_BITMAP_SESSIONID_FILTER	0x00000010
> -#define AUDIT_FEATURE_BITMAP_LOST_RESET		0x00000020
> -#define AUDIT_FEATURE_BITMAP_FILTER_FS		0x00000040
> +#define AUDIT_FEATURE_BITMAP_BACKLOG_LIMIT		0x00000001
> +#define AUDIT_FEATURE_BITMAP_BACKLOG_WAIT_TIME		0x00000002
> +#define AUDIT_FEATURE_BITMAP_EXECUTABLE_PATH		0x00000004
> +#define AUDIT_FEATURE_BITMAP_EXCLUDE_EXTEND		0x00000008
> +#define AUDIT_FEATURE_BITMAP_SESSIONID_FILTER		0x00000010
> +#define AUDIT_FEATURE_BITMAP_LOST_RESET			0x00000020
> +#define AUDIT_FEATURE_BITMAP_FILTER_FS			0x00000040
> +#define AUDIT_FEATURE_BITMAP_EXECUTABLE_PATH_NEQ	0x00000080
> 
>  #define AUDIT_FEATURE_BITMAP_ALL (AUDIT_FEATURE_BITMAP_BACKLOG_LIMIT | \
>  				  AUDIT_FEATURE_BITMAP_BACKLOG_WAIT_TIME | \
> @@ -347,7 +348,8 @@ enum {
>  				  AUDIT_FEATURE_BITMAP_EXCLUDE_EXTEND | \
>  				  AUDIT_FEATURE_BITMAP_SESSIONID_FILTER | \
>  				  AUDIT_FEATURE_BITMAP_LOST_RESET | \
> -				  AUDIT_FEATURE_BITMAP_FILTER_FS)
> +				  AUDIT_FEATURE_BITMAP_FILTER_FS | \
> +				  AUDIT_FEATURE_BITMAP_EXECUTABLE_PATH_NEQ)
> 
>  /* deprecated: AUDIT_VERSION_* */
>  #define AUDIT_VERSION_LATEST 		AUDIT_FEATURE_BITMAP_ALL
> diff --git a/kernel/auditfilter.c b/kernel/auditfilter.c
> index d7a807e81451..a0c5a3ec6e60 100644
> --- a/kernel/auditfilter.c
> +++ b/kernel/auditfilter.c
> @@ -426,7 +426,7 @@ static int audit_field_valid(struct audit_entry *entry,
> struct audit_field *f) return -EINVAL;
>  		break;
>  	case AUDIT_EXE:
> -		if (f->op != Audit_equal)
> +		if (f->op != Audit_not_equal && f->op != Audit_equal)
>  			return -EINVAL;
>  		if (entry->rule.listnr != AUDIT_FILTER_EXIT)
>  			return -EINVAL;
> diff --git a/kernel/auditsc.c b/kernel/auditsc.c
> index 4e0a4ac803db..479c031ec54c 100644
> --- a/kernel/auditsc.c
> +++ b/kernel/auditsc.c
> @@ -471,6 +471,8 @@ static int audit_filter_rules(struct task_struct *tsk,
>  			break;
>  		case AUDIT_EXE:
>  			result = audit_exe_compare(tsk, rule->exe);
> +			if (f->op == Audit_not_equal)
> +				result = !result;
>  			break;
>  		case AUDIT_UID:
>  			result = audit_uid_comparator(cred->uid, f->op, f->uid);