[PATCH] audit: printk USER_AVC messages when audit isn't enabled

[Tyler Hicks]

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
4a4cd633b575609b741a1de7837223a2d9e1c34c ("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.

Signed-off-by: Tyler Hicks <tyhicks at canonical.com>
Cc: Al Viro <viro at zeniv.linux.org.uk>
Cc: Eric Paris <eparis at redhat.com>
Cc: linux-audit at redhat.com
---

It looks like commit 50397bd1e471391d27f64efad9271459c913de87 ("[AUDIT] clean
up audit_receive_msg()") introduced this bug, so I think that this patch should
also get the tag:

  Cc: <stable at kernel.org> # v2.6.25+

Al and Eric, I'll leave that up to you two.


Here's my test matrix showing where messages end up as a result of a call to
libaudit's audit_log_user_avc_message():

		|	unpatched	patched
----------------+--------------------------------
w/o audit=1 &	|	*dropped*	syslog
w/o auditd	|
		|
w/ audit=1 &	|	syslog		syslog
w/o auditd	|
		|
w/o audit=1 &	|	audit.log	audit.log
w/ auditd	|
		|
w/ audit=1 &	|	audit.log	audit.log
w/ auditd	|

Thanks!

 kernel/audit.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/audit.c b/kernel/audit.c
index 91e53d0..f4f2773 100644
--- 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;
 	}
-- 
1.8.3.2