[PATCH] add rule filterkey

Add support for a rule key, which can be used to tie audit records to audit
rules.  This is useful when a watched file is accessed through a link or
symlink, as well as for general audit log analysis.

Because this patch uses a string key instead of an integer key, there is a bit
of extra overhead to do the kstrdup() when a rule fires.  However, we're also
allocating memory for the audit record buffer, so it's probably not that
significant.  I went ahead with a string key because it seems more
user-friendly.

Note that the user must ensure that filterkeys are unique.  The kernel only
checks for duplicate rules.
Signed-off-by: Amy Griffis <amy.griffis@hpd.com>

include/linux/audit.h

@@ -122,6 +122,7 @@
 /* Rule structure sizes -- if these change, different AUDIT_ADD and
  * AUDIT_LIST commands must be implemented. */
 #define AUDIT_MAX_FIELDS   64
+#define AUDIT_MAX_KEY_LEN  32
 #define AUDIT_BITMASK_SIZE 64
 #define AUDIT_WORD(nr) ((__u32)((nr)/32))
 #define AUDIT_BIT(nr)  (1 << ((nr) - AUDIT_WORD(nr)*32))
@@ -171,6 +172,8 @@
 #define AUDIT_ARG2      (AUDIT_ARG0+2)
 #define AUDIT_ARG3      (AUDIT_ARG0+3)
 
+#define AUDIT_FILTERKEY	210
+
 #define AUDIT_NEGATE			0x80000000
 
 /* These are the supported operators.

kernel/audit.h

@@ -81,6 +81,7 @@ struct audit_krule {
 	u32			mask[AUDIT_BITMASK_SIZE];
 	u32			buflen; /* for data alloc on list rules */
 	u32			field_count;
+	char			*filterkey; /* ties events to rules */
 	struct audit_field	*fields;
 	struct audit_field	*inode_f; /* quick access to an inode field */
 	struct audit_watch	*watch;	/* associated watch */

kernel/auditfilter.c

@@ -141,6 +141,7 @@ static inline void audit_free_rule(struct audit_entry *e)
 			selinux_audit_rule_free(f->se_rule);
 		}
 	kfree(e->rule.fields);
+	kfree(e->rule.filterkey);
 	kfree(e);
 }
 
@@ -511,6 +512,16 @@ static struct audit_entry *audit_data_to_entry(struct audit_rule_data *data,
 			if (err)
 				goto exit_free;
 			break;
+		case AUDIT_FILTERKEY:
+			err = -EINVAL;
+			if (entry->rule.filterkey || f->val > AUDIT_MAX_KEY_LEN)
+				goto exit_free;
+			str = audit_unpack_string(&bufp, &remain, f->val);
+			if (IS_ERR(str))
+				goto exit_free;
+			entry->rule.buflen += f->val;
+			entry->rule.filterkey = str;
+			break;
 		default:
 			goto exit_free;
 		}
@@ -612,6 +623,10 @@ static struct audit_rule_data *audit_krule_to_data(struct audit_krule *krule)
 			data->buflen += data->values[i] =
 				audit_pack_string(&bufp, krule->watch->path);
 			break;
+		case AUDIT_FILTERKEY:
+			data->buflen += data->values[i] =
+				audit_pack_string(&bufp, krule->filterkey);
+			break;
 		default:
 			data->values[i] = f->val;
 		}
@@ -651,6 +666,11 @@ static int audit_compare_rule(struct audit_krule *a, struct audit_krule *b)
 			if (strcmp(a->watch->path, b->watch->path))
 				return 1;
 			break;
+		case AUDIT_FILTERKEY:
+			/* both filterkeys exist based on above type compare */
+			if (strcmp(a->filterkey, b->filterkey))
+				return 1;
+			break;
 		default:
 			if (a->fields[i].val != b->fields[i].val)
 				return 1;
@@ -730,6 +750,7 @@ static struct audit_entry *audit_dupe_rule(struct audit_krule *old,
 	u32 fcount = old->field_count;
 	struct audit_entry *entry;
 	struct audit_krule *new;
+	char *fk;
 	int i, err = 0;
 
 	entry = audit_init_entry(fcount);
@@ -760,6 +781,13 @@ static struct audit_entry *audit_dupe_rule(struct audit_krule *old,
 		case AUDIT_SE_CLR:
 			err = audit_dupe_selinux_field(&new->fields[i],
 						       &old->fields[i]);
+			break;
+		case AUDIT_FILTERKEY:
+			fk = kstrdup(old->filterkey, GFP_KERNEL);
+			if (unlikely(!fk))
+				err = -ENOMEM;
+			else
+				new->filterkey = fk;
 		}
 		if (err) {
 			audit_free_rule(entry);
@@ -1245,6 +1273,34 @@ static void audit_list_rules(int pid, int seq, struct sk_buff_head *q)
 		skb_queue_tail(q, skb);
 }
 
+/* Log rule additions and removals */
+static void audit_log_rule_change(uid_t loginuid, u32 sid, char *action,
+				  struct audit_krule *rule, int res)
+{
+	struct audit_buffer *ab;
+
+	ab = audit_log_start(NULL, GFP_KERNEL, AUDIT_CONFIG_CHANGE);
+	if (!ab)
+		return;
+	audit_log_format(ab, "auid=%u", loginuid);
+	if (sid) {
+		char *ctx = NULL;
+		u32 len;
+		if (selinux_ctxid_to_string(sid, &ctx, &len))
+			audit_log_format(ab, " ssid=%u", sid);
+		else
+			audit_log_format(ab, " subj=%s", ctx);
+		kfree(ctx);
+	}
+	audit_log_format(ab, " %s rule key=", action);
+	if (rule->filterkey)
+		audit_log_untrustedstring(ab, rule->filterkey);
+	else
+		audit_log_format(ab, "(null)");
+	audit_log_format(ab, " list=%d res=%d", rule->listnr, res);
+	audit_log_end(ab);
+}
+
 /**
  * audit_receive_filter - apply all rules to the specified message type
  * @type: audit message type
@@ -1304,24 +1360,7 @@ int audit_receive_filter(int type, int pid, int uid, int seq, void *data,
 
 		err = audit_add_rule(entry,
 				     &audit_filter_list[entry->rule.listnr]);
-
-		if (sid) {
-			char *ctx = NULL;
-			u32 len;
-			if (selinux_ctxid_to_string(sid, &ctx, &len)) {
-				/* Maybe call audit_panic? */
-				audit_log(NULL, GFP_KERNEL, AUDIT_CONFIG_CHANGE,
-				 "auid=%u ssid=%u add rule to list=%d res=%d",
-				 loginuid, sid, entry->rule.listnr, !err);
-			} else
-				audit_log(NULL, GFP_KERNEL, AUDIT_CONFIG_CHANGE,
-				 "auid=%u subj=%s add rule to list=%d res=%d",
-				 loginuid, ctx, entry->rule.listnr, !err);
-			kfree(ctx);
-		} else
-			audit_log(NULL, GFP_KERNEL, AUDIT_CONFIG_CHANGE,
-				"auid=%u add rule to list=%d res=%d",
-				loginuid, entry->rule.listnr, !err);
+		audit_log_rule_change(loginuid, sid, "add", &entry->rule, !err);
 
 		if (err)
 			audit_free_rule(entry);
@@ -1337,24 +1376,8 @@ int audit_receive_filter(int type, int pid, int uid, int seq, void *data,
 
 		err = audit_del_rule(entry,
 				     &audit_filter_list[entry->rule.listnr]);
-
-		if (sid) {
-			char *ctx = NULL;
-			u32 len;
-			if (selinux_ctxid_to_string(sid, &ctx, &len)) {
-				/* Maybe call audit_panic? */
-				audit_log(NULL, GFP_KERNEL, AUDIT_CONFIG_CHANGE,
-					"auid=%u ssid=%u remove rule from list=%d res=%d",
-					 loginuid, sid, entry->rule.listnr, !err);
-			} else
-				audit_log(NULL, GFP_KERNEL, AUDIT_CONFIG_CHANGE,
-					"auid=%u subj=%s remove rule from list=%d res=%d",
-					 loginuid, ctx, entry->rule.listnr, !err);
-			kfree(ctx);
-		} else
-			audit_log(NULL, GFP_KERNEL, AUDIT_CONFIG_CHANGE,
-				"auid=%u remove rule from list=%d res=%d",
-				loginuid, entry->rule.listnr, !err);
+		audit_log_rule_change(loginuid, sid, "remove", &entry->rule,
+				      !err);
 
 		audit_free_rule(entry);
 		break;

kernel/auditsc.c

@@ -186,6 +186,7 @@ struct audit_context {
 	int		    auditable;  /* 1 if record should be written */
 	int		    name_count;
 	struct audit_names  names[AUDIT_NAMES];
+	char *		    filterkey;	/* key for rule that triggered record */
 	struct dentry *	    pwd;
 	struct vfsmount *   pwdmnt;
 	struct audit_context *previous; /* For nested syscalls */
@@ -348,11 +349,17 @@ static int audit_filter_rules(struct task_struct *tsk,
 			if (ctx)
 				result = audit_comparator(ctx->argv[f->type-AUDIT_ARG0], f->op, f->val);
 			break;
+		case AUDIT_FILTERKEY:
+			/* ignore this field for filtering */
+			result = 1;
+			break;
 		}
 
 		if (!result)
 			return 0;
 	}
+	if (rule->filterkey)
+		ctx->filterkey = kstrdup(rule->filterkey, GFP_ATOMIC);
 	switch (rule->action) {
 	case AUDIT_NEVER:    *state = AUDIT_DISABLED;	    break;
 	case AUDIT_ALWAYS:   *state = AUDIT_RECORD_CONTEXT; break;
@@ -627,6 +634,7 @@ static inline void audit_free_context(struct audit_context *context)
 		}
 		audit_free_names(context);
 		audit_free_aux(context);
+		kfree(context->filterkey);
 		kfree(context);
 		context  = previous;
 	} while (context);
@@ -735,6 +743,11 @@ static void audit_log_exit(struct audit_context *context, struct task_struct *ts
 		  context->euid, context->suid, context->fsuid,
 		  context->egid, context->sgid, context->fsgid, tty);
 	audit_log_task_info(ab, tsk);
+	if (context->filterkey) {
+		audit_log_format(ab, " key=");
+		audit_log_untrustedstring(ab, context->filterkey);
+	} else
+		audit_log_format(ab, " key=(null)");
 	audit_log_end(ab);
 
 	for (aux = context->aux; aux; aux = aux->next) {
@@ -1060,6 +1073,8 @@ void audit_syscall_exit(int valid, long return_code)
 	} else {
 		audit_free_names(context);
 		audit_free_aux(context);
+		kfree(context->filterkey);
+		context->filterkey = NULL;
 		tsk->audit_context = context;
 	}
 }