[PATCH V4] audit: add feature audit_lost reset

[Richard Guy Briggs]

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.  The return value will be the +ve lost value at
reset time.

An AUDIT_CONFIG_CHANGE message will be queued to the listening audit
daemon.  The message will be a standard CONFIG_CHANGE message with the
fields "lost=0" and "old=" with the latter containing the value of
audit_lost at reset time.

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

Signed-off-by: Richard Guy Briggs <rgb at redhat.com>
---
There is a merge conflict anticipated with the exclude filter
FEATURE_BITMAP patch (ghak5)

v2:
   Switch from AUDIT_GET to AUDIT_SET
   Remove AUDIT_FEATURE and AUDIT_FEATURE_BITMAP
   Return +ve lost value, reply AUDIT_LOST_RESET msg to sender

v3:
   Switch, from reply to sender, to queue to audit log

v4:
   Switch from LOST_RESET to CONFIG_CHANGE log msg
   Re-add AUDIT_FEATURE_BITMASK
---
---
 include/uapi/linux/audit.h |    6 +++++-
 kernel/audit.c             |    8 +++++++-
 2 files changed, 12 insertions(+), 2 deletions(-)

diff --git a/include/uapi/linux/audit.h b/include/uapi/linux/audit.h
index c8dc97b..3f24110 100644
--- a/include/uapi/linux/audit.h
+++ b/include/uapi/linux/audit.h
@@ -326,15 +326,19 @@ 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
 #define AUDIT_FEATURE_BITMAP_EXECUTABLE_PATH	0x00000004
 #define AUDIT_FEATURE_BITMAP_SESSIONID_FILTER	0x00000010
+#define AUDIT_FEATURE_BITMAP_LOST_RESET		0x00000020
+
 #define AUDIT_FEATURE_BITMAP_ALL (AUDIT_FEATURE_BITMAP_BACKLOG_LIMIT | \
 				  AUDIT_FEATURE_BITMAP_BACKLOG_WAIT_TIME | \
 				  AUDIT_FEATURE_BITMAP_EXECUTABLE_PATH | \
-				  AUDIT_FEATURE_BITMAP_SESSIONID_FILTER)
+				  AUDIT_FEATURE_BITMAP_SESSIONID_FILTER | \
+				  AUDIT_FEATURE_BITMAP_LOST_RESET)
 
 /* deprecated: AUDIT_VERSION_* */
 #define AUDIT_VERSION_LATEST 		AUDIT_FEATURE_BITMAP_ALL
diff --git a/kernel/audit.c b/kernel/audit.c
index 57acf25..25dd70a 100644
--- a/kernel/audit.c
+++ b/kernel/audit.c
@@ -121,7 +121,7 @@ u32		audit_sig_sid = 0;
    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;
@@ -1052,6 +1052,12 @@ 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_log_config_change("lost", 0, lost, 1);
+			return lost;
+		}
 		break;
 	}
 	case AUDIT_GET_FEATURE:
-- 
1.7.1