audit: tidy and extend netfilter_cfg x_tables

NETFILTER_CFG record generation was inconsistent for x_tables and
ebtables configuration changes.  The call was needlessly messy and there
were supporting records missing at times while they were produced when
not requested.  Simplify the logging call into a new audit_log_nfcfg
call.  Honour the audit_enabled setting while more consistently
recording information including supporting records by tidying up dummy
checks.

Add an op= field that indicates the operation being performed (register
or replace).

Here is the enhanced sample record:
  type=NETFILTER_CFG msg=audit(1580905834.919:82970): table=filter family=2 entries=83 op=replace

Generate audit NETFILTER_CFG records on ebtables table registration.
Previously this was being done for x_tables registration and replacement
operations and ebtables table replacement only.

See: linux-audit/audit-kernel#25
See: linux-audit/audit-kernel#35
See: linux-audit/audit-kernel#43

Signed-off-by: Richard Guy Briggs <[email protected]>
Signed-off-by: Paul Moore <[email protected]>

include/linux/audit.h

@@ -94,6 +94,11 @@ struct audit_ntp_data {
 struct audit_ntp_data {};
 #endif
 
+enum audit_nfcfgop {
+	AUDIT_XT_OP_REGISTER,
+	AUDIT_XT_OP_REPLACE,
+};
+
 extern int is_audit_feature_set(int which);
 
 extern int __init audit_register_class(int class, unsigned *list);
@@ -379,6 +384,8 @@ extern void __audit_log_kern_module(char *name);
 extern void __audit_fanotify(unsigned int response);
 extern void __audit_tk_injoffset(struct timespec64 offset);
 extern void __audit_ntp_log(const struct audit_ntp_data *ad);
+extern void __audit_log_nfcfg(const char *name, u8 af, unsigned int nentries,
+			      enum audit_nfcfgop op);
 
 static inline void audit_ipc_obj(struct kern_ipc_perm *ipcp)
 {
@@ -514,6 +521,14 @@ static inline void audit_ntp_log(const struct audit_ntp_data *ad)
 		__audit_ntp_log(ad);
 }
 
+static inline void audit_log_nfcfg(const char *name, u8 af,
+				   unsigned int nentries,
+				   enum audit_nfcfgop op)
+{
+	if (audit_enabled)
+		__audit_log_nfcfg(name, af, nentries, op);
+}
+
 extern int audit_n_rules;
 extern int audit_signals;
 #else /* CONFIG_AUDITSYSCALL */
@@ -646,6 +661,12 @@ static inline void audit_ntp_log(const struct audit_ntp_data *ad)
 
 static inline void audit_ptrace(struct task_struct *t)
 { }
+
+static inline void audit_log_nfcfg(const char *name, u8 af,
+				   unsigned int nentries,
+				   enum audit_nfcfgop op)
+{ }
+
 #define audit_n_rules 0
 #define audit_signals 0
 #endif /* CONFIG_AUDITSYSCALL */

kernel/auditsc.c

@@ -130,6 +130,16 @@ struct audit_tree_refs {
 	struct audit_chunk *c[31];
 };
 
+struct audit_nfcfgop_tab {
+	enum audit_nfcfgop	op;
+	const char		*s;
+};
+
+const struct audit_nfcfgop_tab audit_nfcfgs[] = {
+	{ AUDIT_XT_OP_REGISTER,	"register"	},
+	{ AUDIT_XT_OP_REPLACE,	"replace"	},
+};
+
 static int audit_match_perm(struct audit_context *ctx, int mask)
 {
 	unsigned n;
@@ -2542,6 +2552,20 @@ void __audit_ntp_log(const struct audit_ntp_data *ad)
 	audit_log_ntp_val(ad, "adjust",	AUDIT_NTP_ADJUST);
 }
 
+void __audit_log_nfcfg(const char *name, u8 af, unsigned int nentries,
+		       enum audit_nfcfgop op)
+{
+	struct audit_buffer *ab;
+
+	ab = audit_log_start(audit_context(), GFP_KERNEL, AUDIT_NETFILTER_CFG);
+	if (!ab)
+		return;
+	audit_log_format(ab, "table=%s family=%u entries=%u op=%s",
+			 name, af, nentries, audit_nfcfgs[op].s);
+	audit_log_end(ab);
+}
+EXPORT_SYMBOL_GPL(__audit_log_nfcfg);
+
 static void audit_log_task(struct audit_buffer *ab)
 {
 	kuid_t auid, uid;

net/bridge/netfilter/ebtables.c

@@ -1046,14 +1046,8 @@ static int do_replace_finish(struct net *net, struct ebt_replace *repl,
 	vfree(table);
 	vfree(counterstmp);
 
-#ifdef CONFIG_AUDIT
-	if (audit_enabled) {
-		audit_log(audit_context(), GFP_KERNEL,
-			  AUDIT_NETFILTER_CFG,
-			  "table=%s family=%u entries=%u",
-			  repl->name, AF_BRIDGE, repl->nentries);
-	}
-#endif
+	audit_log_nfcfg(repl->name, AF_BRIDGE, repl->nentries,
+			AUDIT_XT_OP_REPLACE);
 	return ret;
 
 free_unlock:
@@ -1223,6 +1217,8 @@ int ebt_register_table(struct net *net, const struct ebt_table *input_table,
 		*res = NULL;
 	}
 
+	audit_log_nfcfg(repl->name, AF_BRIDGE, repl->nentries,
+			AUDIT_XT_OP_REGISTER);
 	return ret;
 free_unlock:
 	mutex_unlock(&ebt_mutex);

net/netfilter/x_tables.c

@@ -1408,15 +1408,9 @@ xt_replace_table(struct xt_table *table,
 		}
 	}
 
-#ifdef CONFIG_AUDIT
-	if (audit_enabled) {
-		audit_log(audit_context(), GFP_KERNEL,
-			  AUDIT_NETFILTER_CFG,
-			  "table=%s family=%u entries=%u",
-			  table->name, table->af, private->number);
-	}
-#endif
-
+	audit_log_nfcfg(table->name, table->af, private->number,
+			!private->number ? AUDIT_XT_OP_REGISTER :
+					   AUDIT_XT_OP_REPLACE);
 	return private;
 }
 EXPORT_SYMBOL_GPL(xt_replace_table);