audit: printk USER_AVC messages when audit isn't enabled

commit 0868a5e150bc4c47e7a003367cd755811eb41e0b upstream.

When the audit=1 kernel parameter is absent and auditd is not running,
AUDIT_USER_AVC messages are being silently discarded.

AUDIT_USER_AVC messages should be sent to userspace using printk(), as
mentioned in the commit message of 4a4cd633 ("AUDIT: Optimise the
audit-disabled case for discarding user messages").

When audit_enabled is 0, audit_receive_msg() discards all user messages
except for AUDIT_USER_AVC messages. However, audit_log_common_recv_msg()
refuses to allocate an audit_buffer if audit_enabled is 0. The fix is to
special case AUDIT_USER_AVC messages in both functions.

It looks like commit 50397bd1 ("[AUDIT] clean up audit_receive_msg()")
introduced this bug.

Signed-off-by: Tyler Hicks <tyhicks@canonical.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Eric Paris <eparis@redhat.com>
Cc: linux-audit@redhat.com
Acked-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Richard Guy Briggs <rgb@redhat.com>
Signed-off-by: Eric Paris <eparis@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/kernel/audit.c b/kernel/audit.c
index 7b0e23a740ce345987c33f9e012302c24de0f4db..f5dc4b5db72e01c41d624f8cae279e96f41b45ec 100644 (file)
--- a/kernel/audit.c
+++ b/kernel/audit.c
@@ -613,7 +613,7 @@ static int audit_log_common_recv_msg(struct audit_buffer **ab, u16 msg_type)
        int rc = 0;
        uid_t uid = from_kuid(&init_user_ns, current_uid());
 
-       if (!audit_enabled) {
+       if (!audit_enabled && msg_type != AUDIT_USER_AVC) {
                *ab = NULL;
                return rc;
        }