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 <[email protected]> Signed-off-by: Richard Guy Briggs <[email protected]> Signed-off-by: Eric Paris <[email protected]>
ambv · Nov 5, 2013 · 81407c8 · 81407c8
1 parent 83fa6bb
commit 81407c8
Show file tree

Hide file tree

Showing 2 changed files with 13 additions and 5 deletions.
diff --git a/fs/proc/base.c b/fs/proc/base.c
@@ -1151,10 +1151,16 @@ static ssize_t proc_loginuid_write(struct file * file, const char __user * buf,
 		goto out_free_page;
 
 	}
-	kloginuid = make_kuid(file->f_cred->user_ns, loginuid);
-	if (!uid_valid(kloginuid)) {
-		length = -EINVAL;
-		goto out_free_page;
+
+	/* is userspace tring to explicitly UNSET the loginuid? */
+	if (loginuid == AUDIT_UID_UNSET) {
+		kloginuid = INVALID_UID;
+	} else {
+		kloginuid = make_kuid(file->f_cred->user_ns, loginuid);
+		if (!uid_valid(kloginuid)) {
+			length = -EINVAL;
+			goto out_free_page;
+		}
 	}
 
 	length = audit_set_loginuid(kloginuid);

diff --git 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;