[PATCH v6] audit: log AUDIT_TIME_* records only from rules

[Richard Guy Briggs]

AUDIT_TIME_* events are generated when there are syscall rules present
that are not related to time keeping.  This will produce noisy log
entries that could flood the logs and hide events we really care about.

Rather than immediately produce the AUDIT_TIME_* records, store the data
in the context and log it at syscall exit time respecting the filter
rules.

Note: This eats the audit_buffer, unlike any others in show_special().

Please see https://bugzilla.redhat.com/show_bug.cgi?id=1991919

Fixes: 7e8eda734d30 ("ntp: Audit NTP parameters adjustment")
Fixes: 2d87a0674bd6 ("timekeeping: Audit clock adjustments")
Signed-off-by: Richard Guy Briggs <rgb at redhat.com>
---
Changelog:
v2:
- rename __audit_ntp_log_ to audit_log_ntp
- pre-check ntp before storing
- move tk out of the context union and move ntp logging to the bottom of audit_show_special()
- restructure logging of ntp to use ab and allocate more only if more
- add Fixes lines
v3
- move tk into union
- rename audit_log_ntp() to audit_log_time() and add tk
- key off both AUDIT_TIME_* but favour NTP
v4
- drop tk goto in favour of ntp if clause
- add comments to clarify calling function buffer expectations
v5
- hold my nose and swallow the audit_buffer in audit_log_time()
v6
- declare audit_log_time() and ntp_name as static

 kernel/audit.h   |  4 +++
 kernel/auditsc.c | 85 ++++++++++++++++++++++++++++++++++++------------
 2 files changed, 69 insertions(+), 20 deletions(-)

diff --git a/kernel/audit.h b/kernel/audit.h
index c4498090a5bd..58b66543b4d5 100644
--- a/kernel/audit.h
+++ b/kernel/audit.h
@@ -201,6 +201,10 @@ struct audit_context {
 		struct {
 			char			*name;
 		} module;
+		struct {
+			struct audit_ntp_data	ntp_data;
+			struct timespec64	tk_injoffset;
+		} time;
 	};
 	int fds[2];
 	struct audit_proctitle proctitle;
diff --git a/kernel/auditsc.c b/kernel/auditsc.c
index fce5d43a933f..e928d94796e5 100644
--- a/kernel/auditsc.c
+++ b/kernel/auditsc.c
@@ -1340,6 +1340,51 @@ static void audit_log_fcaps(struct audit_buffer *ab, struct audit_names *name)
 			 from_kuid(&init_user_ns, name->fcap.rootid));
 }
 
+static void audit_log_time(struct audit_context *context, struct audit_buffer **ab)
+{
+	const struct audit_ntp_data *ntp = &context->time.ntp_data;
+	const struct timespec64 *tk = &context->time.tk_injoffset;
+	static const char * const ntp_name[] = {
+		"offset",
+		"freq",
+		"status",
+		"tai",
+		"tick",
+		"adjust",
+	};
+	int type;
+
+	if (context->type == AUDIT_TIME_ADJNTPVAL) {
+		for (type = 0; type < AUDIT_NTP_NVALS; type++) {
+			if (ntp->vals[type].newval != ntp->vals[type].oldval) {
+				if (!*ab) {
+					*ab = audit_log_start(context, GFP_KERNEL,
+							      AUDIT_TIME_ADJNTPVAL);
+					if (!*ab)
+						return;
+				}
+				audit_log_format(*ab, "op=%s old=%lli new=%lli",
+						 ntp_name[type], ntp->vals[type].oldval,
+						 ntp->vals[type].newval);
+				audit_log_end(*ab);
+				*ab = NULL;
+			}
+		}
+	}
+	if (tk->tv_sec != 0 || tk->tv_nsec != 0) {
+		if (!*ab) {
+			*ab = audit_log_start(context, GFP_KERNEL,
+					      AUDIT_TIME_INJOFFSET);
+			if (!*ab)
+				return;
+		}
+		audit_log_format(*ab, "sec=%lli nsec=%li",
+				 (long long)tk->tv_sec, tk->tv_nsec);
+		audit_log_end(*ab);
+		*ab = NULL;
+	}
+}
+
 static void show_special(struct audit_context *context, int *call_panic)
 {
 	struct audit_buffer *ab;
@@ -1454,6 +1499,11 @@ static void show_special(struct audit_context *context, int *call_panic)
 			audit_log_format(ab, "(null)");
 
 		break;
+	case AUDIT_TIME_ADJNTPVAL:
+	case AUDIT_TIME_INJOFFSET:
+		/* this call deviates from the rest, eating the buffer */
+		audit_log_time(context, &ab);
+		break;
 	}
 	audit_log_end(ab);
 }
@@ -2849,31 +2899,26 @@ void __audit_fanotify(unsigned int response)
 
 void __audit_tk_injoffset(struct timespec64 offset)
 {
-	audit_log(audit_context(), GFP_KERNEL, AUDIT_TIME_INJOFFSET,
-		  "sec=%lli nsec=%li",
-		  (long long)offset.tv_sec, offset.tv_nsec);
-}
-
-static void audit_log_ntp_val(const struct audit_ntp_data *ad,
-			      const char *op, enum audit_ntp_type type)
-{
-	const struct audit_ntp_val *val = &ad->vals[type];
-
-	if (val->newval == val->oldval)
-		return;
+	struct audit_context *context = audit_context();
 
-	audit_log(audit_context(), GFP_KERNEL, AUDIT_TIME_ADJNTPVAL,
-		  "op=%s old=%lli new=%lli", op, val->oldval, val->newval);
+	/* only set type if not already set by NTP */
+	if (!context->type)
+		context->type = AUDIT_TIME_INJOFFSET;
+	memcpy(&context->time.tk_injoffset, &offset, sizeof(offset));
 }
 
 void __audit_ntp_log(const struct audit_ntp_data *ad)
 {
-	audit_log_ntp_val(ad, "offset",	AUDIT_NTP_OFFSET);
-	audit_log_ntp_val(ad, "freq",	AUDIT_NTP_FREQ);
-	audit_log_ntp_val(ad, "status",	AUDIT_NTP_STATUS);
-	audit_log_ntp_val(ad, "tai",	AUDIT_NTP_TAI);
-	audit_log_ntp_val(ad, "tick",	AUDIT_NTP_TICK);
-	audit_log_ntp_val(ad, "adjust",	AUDIT_NTP_ADJUST);
+	struct audit_context *context = audit_context();
+	int type;
+
+	for (type = 0; type < AUDIT_NTP_NVALS; type++)
+		if (ad->vals[type].newval != ad->vals[type].oldval) {
+			/* unconditionally set type, overwriting TK */
+			context->type = AUDIT_TIME_ADJNTPVAL;
+			memcpy(&context->time.ntp_data, ad, sizeof(*ad));
+			break;
+		}
 }
 
 void __audit_log_nfcfg(const char *name, u8 af, unsigned int nentries,
-- 
2.27.0