[PATCH 7/7] audit: audit feature to set loginuid immutable

[Eric Paris <eparis@redhat.com>]

This adds a new 'audit_feature' bit which allows userspace to set it
such that the loginuid is absolutely immutable, even if you have
CAP_AUDIT_CONTROL.

Signed-off-by: Eric Paris <eparis@redhat.com>
---
 include/uapi/linux/audit.h | 3 ++-
 kernel/audit.c             | 3 ++-
 kernel/auditsc.c           | 3 +++
 3 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/include/uapi/linux/audit.h b/include/uapi/linux/audit.h
index 2963b5a..9539ea9 100644
--- a/include/uapi/linux/audit.h
+++ b/include/uapi/linux/audit.h
@@ -381,7 +381,8 @@ struct audit_features {
 };
 
 #define AUDIT_FEATURE_ONLY_UNSET_LOGINUID	0
-#define AUDIT_LAST_FEATURE			AUDIT_FEATURE_ONLY_UNSET_LOGINUID
+#define AUDIT_FEATURE_LOGINUID_IMMUTABLE	1
+#define AUDIT_LAST_FEATURE			AUDIT_FEATURE_LOGINUID_IMMUTABLE
 
 #define audit_feature_valid(x)		((x) >= 0 && (x) <= AUDIT_LAST_FEATURE)
 #define AUDIT_FEATURE_TO_MASK(x)	(1 << ((x) & 31)) /* mask for __u32 */
diff --git a/kernel/audit.c b/kernel/audit.c
index a5c470b..900d61d 100644
--- a/kernel/audit.c
+++ b/kernel/audit.c
@@ -145,8 +145,9 @@ static struct audit_features af = {.vers = AUDIT_FEATURE_VERSION,
 				   .features = 0,
 				   .lock = 0,};
 
-static char *audit_feature_names[1] = {
+static char *audit_feature_names[2] = {
 	"only_unset_loginuid",
+	"loginuid_immutable",
 };
 
 
diff --git a/kernel/auditsc.c b/kernel/auditsc.c
index e5dbbc6..aace3ac 100644
--- a/kernel/auditsc.c
+++ b/kernel/auditsc.c
@@ -1969,6 +1969,9 @@ static int audit_set_loginuid_perm(kuid_t loginuid)
 	/* if we are unset, we don't need privs */
 	if (!audit_loginuid_set(current))
 		return 0;
+	/* if AUDIT_FEATURE_LOGINUID_IMMUTABLE means never ever allow a change*/
+	if (is_audit_feature_set(AUDIT_FEATURE_LOGINUID_IMMUTABLE))
+		return -EPERM;
 	/* it is set, you need permission */
 	if (!capable(CAP_AUDIT_CONTROL))
 		return -EPERM;
-- 
1.8.2.1