[PATCH 6/7] audit: audit feature to only allow unsetting the loginuid

Eric Paris
2013-05-24T16:11:49Z

This is a new audit feature which only grants processes with
CAP_AUDIT_CONTROL the ability to unset their loginuid. They cannot
directly set it from a valid uid to another valid uid. The ability to
unset the loginuid is nice because a priviledged task, like that of
container creation, can unset the loginuid and then priv is not needed
inside the container when a login daemon needs to set the loginuid.

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 a053243..2963b5a 100644
--- a/include/uapi/linux/audit.h
+++ b/include/uapi/linux/audit.h
@@ -380,7 +380,8 @@ struct audit_features {
__u32 lock; /* which features to lock */
};

-#define AUDIT_LAST_FEATURE -1
+#define AUDIT_FEATURE_ONLY_UNSET_LOGINUID 0
+#define AUDIT_LAST_FEATURE AUDIT_FEATURE_ONLY_UNSET_LOGINUID

#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 3acbbc8..a5c470b 100644
--- a/kernel/audit.c
+++ b/kernel/audit.c
@@ -145,7 +145,8 @@ static struct audit_features af = {.vers = AUDIT_FEATURE_VERSION,
.features = 0,
.lock = 0,};

-static char *audit_feature_names[0] = {
+static char *audit_feature_names[1] = {
+ "only_unset_loginuid",
};

diff --git a/kernel/auditsc.c b/kernel/auditsc.c
index eea28c1..e5dbbc6 100644
--- a/kernel/auditsc.c
+++ b/kernel/auditsc.c
@@ -1972,6 +1972,9 @@ static int audit_set_loginuid_perm(kuid_t loginuid)
/* it is set, you need permission */
if (!capable(CAP_AUDIT_CONTROL))
return -EPERM;
+ /* reject if this is not an unset and we don't allow that */
+ if (is_audit_feature_set(AUDIT_FEATURE_ONLY_UNSET_LOGINUID) && uid_valid(loginuid))
+ return -EPERM;
return 0;
}

--
1.8.2.1