audit: move loginuid and sessionid from CONFIG_AUDITSYSCALL to CONFIG_AUDIT

loginuid and sessionid (and audit_log_session_info) should be part of
CONFIG_AUDIT scope and not CONFIG_AUDITSYSCALL since it is used in
CONFIG_CHANGE, ANOM_LINK, FEATURE_CHANGE (and INTEGRITY_RULE), none of
which are otherwise dependent on AUDITSYSCALL.

Please see github issue
https://github.com/linux-audit/audit-kernel/issues/104

Signed-off-by: Richard Guy Briggs <rgb@redhat.com>
[PM: tweaked subject line for better grep'ing]
Signed-off-by: Paul Moore <paul@paul-moore.com>

1 files changed, 85 insertions, 0 deletions

diff --git a/kernel/audit.c b/kernel/audit.c
index c2a7662cc254..2a32f304223d 100644
--- a/kernel/audit.c
+++ b/kernel/audit.c
@@ -2335,6 +2335,91 @@ void audit_log_link_denied(const char *operation)
 	audit_log_end(ab);
 }
 
+/* global counter which is incremented every time something logs in */
+static atomic_t session_id = ATOMIC_INIT(0);
+
+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;
+	/* 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;
+}
+
+static void audit_log_set_loginuid(kuid_t koldloginuid, kuid_t kloginuid,
+				   unsigned int oldsessionid,
+				   unsigned int sessionid, int rc)
+{
+	struct audit_buffer *ab;
+	uid_t uid, oldloginuid, loginuid;
+	struct tty_struct *tty;
+
+	if (!audit_enabled)
+		return;
+
+	ab = audit_log_start(NULL, GFP_KERNEL, AUDIT_LOGIN);
+	if (!ab)
+		return;
+
+	uid = from_kuid(&init_user_ns, task_uid(current));
+	oldloginuid = from_kuid(&init_user_ns, koldloginuid);
+	loginuid = from_kuid(&init_user_ns, kloginuid),
+	tty = audit_get_tty();
+
+	audit_log_format(ab, "pid=%d uid=%u", task_tgid_nr(current), uid);
+	audit_log_task_context(ab);
+	audit_log_format(ab, " old-auid=%u auid=%u tty=%s old-ses=%u ses=%u res=%d",
+			 oldloginuid, loginuid, tty ? tty_name(tty) : "(none)",
+			 oldsessionid, sessionid, !rc);
+	audit_put_tty(tty);
+	audit_log_end(ab);
+}
+
+/**
+ * audit_set_loginuid - set current task's loginuid
+ * @loginuid: loginuid value
+ *
+ * Returns 0.
+ *
+ * Called (set) from fs/proc/base.c::proc_loginuid_write().
+ */
+int audit_set_loginuid(kuid_t loginuid)
+{
+	unsigned int oldsessionid, sessionid = AUDIT_SID_UNSET;
+	kuid_t oldloginuid;
+	int rc;
+
+	oldloginuid = audit_get_loginuid(current);
+	oldsessionid = audit_get_sessionid(current);
+
+	rc = audit_set_loginuid_perm(loginuid);
+	if (rc)
+		goto out;
+
+	/* are we setting or clearing? */
+	if (uid_valid(loginuid)) {
+		sessionid = (unsigned int)atomic_inc_return(&session_id);
+		if (unlikely(sessionid == AUDIT_SID_UNSET))
+			sessionid = (unsigned int)atomic_inc_return(&session_id);
+	}
+
+	current->sessionid = sessionid;
+	current->loginuid = loginuid;
+out:
+	audit_log_set_loginuid(oldloginuid, loginuid, oldsessionid, sessionid, rc);
+	return rc;
+}
+
 /**
  * audit_log_end - end one audit record
  * @ab: the audit_buffer