audit: audit feature to set loginuid immutable

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>
Signed-off-by: Richard Guy Briggs <rgb@redhat.com>
Signed-off-by: Eric Paris <eparis@redhat.com>

3 files changed, 7 insertions, 2 deletions

diff --git a/include/uapi/linux/audit.h b/include/uapi/linux/audit.h
index 05e5e8fc2ac4..e2f0d9977131 100644
--- a/include/uapi/linux/audit.h
+++ b/include/uapi/linux/audit.h
@@ -387,7 +387,8 @@ 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 fbfa3a74decb..f3f36f5eb4ae 100644
--- a/kernel/audit.c
+++ b/kernel/audit.c
@@ -144,8 +144,9 @@ 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 924c0bf048d2..63223d671a6e 100644
--- a/kernel/auditsc.c
+++ b/kernel/auditsc.c
@@ -1971,6 +1971,9 @@ 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;