audit: allow unsetting the loginuid (with priv)

If a task has CAP_AUDIT_CONTROL allow that task to unset their loginuid.
This would allow a child of that task to set their loginuid without
CAP_AUDIT_CONTROL.  Thus when launching a new login daemon, a
priviledged helper would be able to unset the loginuid and then the
daemon, which may be malicious user facing, do not need priv to function
correctly.

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>

1 files changed, 3 insertions, 1 deletions

diff --git a/kernel/auditsc.c b/kernel/auditsc.c
index b55788bf1607..c75d7813aef2 100644
--- a/kernel/auditsc.c
+++ b/kernel/auditsc.c
@@ -2019,7 +2019,9 @@ int audit_set_loginuid(kuid_t loginuid)
         if (rc)
                 goto out;
 
-        sessionid = atomic_inc_return(&session_id);
+        /* are we setting or clearing? */
+        if (uid_valid(loginuid))
+                sessionid = atomic_inc_return(&session_id);
 
         task->sessionid = sessionid;
         task->loginuid = loginuid;