[PATCH v2] audit: add feature audit_lost reset

[Richard Guy Briggs <rgb@redhat.com>]

Add a method to reset the audit_lost value.

An AUDIT_SET message with the AUDIT_STATUS_LOST flag set by itself
will return a positive value repesenting the current audit_lost value
and reset the counter to zero.  If AUDIT_STATUS_LOST is not the
only flag set, the reset command will be ignored.  The value sent with
the command is ignored.

An AUDIT_LOST_RESET message will be sent to the listening audit daemon.
The data field will contain a u32 with the positive value of the
audit_lost value when it was reset.

See: https://github.com/linux-audit/audit-kernel/issues/3

Signed-off-by: Richard Guy Briggs <rgb@redhat.com>
---
 include/uapi/linux/audit.h |    2 ++
 kernel/audit.c             |    8 +++++++-
 2 files changed, 9 insertions(+), 1 deletions(-)

diff --git a/include/uapi/linux/audit.h b/include/uapi/linux/audit.h
index 208df7b..6d38bff 100644
--- a/include/uapi/linux/audit.h
+++ b/include/uapi/linux/audit.h
@@ -70,6 +70,7 @@
 #define AUDIT_TTY_SET		1017	/* Set TTY auditing status */
 #define AUDIT_SET_FEATURE	1018	/* Turn an audit feature on or off */
 #define AUDIT_GET_FEATURE	1019	/* Get which features are enabled */
+#define AUDIT_LOST_RESET	1020	/* Reset the audit_lost value */
 
 #define AUDIT_FIRST_USER_MSG	1100	/* Userspace messages mostly uninteresting to kernel */
 #define AUDIT_USER_AVC		1107	/* We filter this differently */
@@ -325,6 +326,7 @@ enum {
 #define AUDIT_STATUS_RATE_LIMIT		0x0008
 #define AUDIT_STATUS_BACKLOG_LIMIT	0x0010
 #define AUDIT_STATUS_BACKLOG_WAIT_TIME	0x0020
+#define AUDIT_STATUS_LOST		0x0040
 
 #define AUDIT_FEATURE_BITMAP_BACKLOG_LIMIT	0x00000001
 #define AUDIT_FEATURE_BITMAP_BACKLOG_WAIT_TIME	0x00000002
diff --git a/kernel/audit.c b/kernel/audit.c
index f1ca116..19cfee0 100644
--- a/kernel/audit.c
+++ b/kernel/audit.c
@@ -122,7 +122,7 @@
    3) suppressed due to audit_rate_limit
    4) suppressed due to audit_backlog_limit
 */
-static atomic_t    audit_lost = ATOMIC_INIT(0);
+static atomic_t	audit_lost = ATOMIC_INIT(0);
 
 /* The netlink socket. */
 static struct sock *audit_sock;
@@ -920,6 +920,12 @@ static int audit_receive_msg(struct sk_buff *skb, struct nlmsghdr *nlh)
 			if (err < 0)
 				return err;
 		}
+		if (s.mask == AUDIT_STATUS_LOST) {
+			u32 lost = atomic_xchg(&audit_lost, 0);
+
+			audit_send_reply(skb, seq, AUDIT_LOST_RESET, 0, 0, &lost, sizeof(lost));
+			return lost;
+		}
 		break;
 	}
 	case AUDIT_GET_FEATURE:
-- 
1.7.1