audit: filter PATH records keyed on filesystem magic

Tracefs or debugfs were causing hundreds to thousands of PATH records to
be associated with the init_module and finit_module SYSCALL records on a
few modules when the following rule was in place for startup:
	-a always,exit -F arch=x86_64 -S init_module -F key=mod-load

Provide a method to ignore these large number of PATH records from
overwhelming the logs if they are not of interest.  Introduce a new
filter list "AUDIT_FILTER_FS", with a new field type AUDIT_FSTYPE,
which keys off the filesystem 4-octet hexadecimal magic identifier to
filter specific filesystem PATH records.

An example rule would look like:
	-a never,filesystem -F fstype=0x74726163 -F key=ignore_tracefs
	-a never,filesystem -F fstype=0x64626720 -F key=ignore_debugfs

Arguably the better way to address this issue is to disable tracefs and
debugfs on boot from production systems.

See: https://github.com/linux-audit/audit-kernel/issues/16
See: https://github.com/linux-audit/audit-userspace/issues/8
Test case: https://github.com/linux-audit/audit-testsuite/issues/42

Signed-off-by: Richard Guy Briggs <rgb@redhat.com>
[PM: fixed the whitespace damage in kernel/auditsc.c]
Signed-off-by: Paul Moore <paul@paul-moore.com>

2 files changed, 55 insertions, 7 deletions

diff --git a/kernel/auditfilter.c b/kernel/auditfilter.c
index 0b0aa5854dac..4a1758adb222 100644
--- a/kernel/auditfilter.c
+++ b/kernel/auditfilter.c
@@ -56,7 +56,8 @@ struct list_head audit_filter_list[AUDIT_NR_FILTERS] = {
 	LIST_HEAD_INIT(audit_filter_list[3]),
 	LIST_HEAD_INIT(audit_filter_list[4]),
 	LIST_HEAD_INIT(audit_filter_list[5]),
-#if AUDIT_NR_FILTERS != 6
+	LIST_HEAD_INIT(audit_filter_list[6]),
+#if AUDIT_NR_FILTERS != 7
 #error Fix audit_filter_list initialiser
 #endif
 };
@@ -67,6 +68,7 @@ static struct list_head audit_rules_list[AUDIT_NR_FILTERS] = {
 	LIST_HEAD_INIT(audit_rules_list[3]),
 	LIST_HEAD_INIT(audit_rules_list[4]),
 	LIST_HEAD_INIT(audit_rules_list[5]),
+	LIST_HEAD_INIT(audit_rules_list[6]),
 };
 
 DEFINE_MUTEX(audit_filter_mutex);
@@ -263,6 +265,7 @@ static inline struct audit_entry *audit_to_entry_common(struct audit_rule_data *
 #endif
 	case AUDIT_FILTER_USER:
 	case AUDIT_FILTER_TYPE:
+	case AUDIT_FILTER_FS:
 		;
 	}
 	if (unlikely(rule->action == AUDIT_POSSIBLE)) {
@@ -338,6 +341,21 @@ static int audit_field_valid(struct audit_entry *entry, struct audit_field *f)
 		    entry->rule.listnr != AUDIT_FILTER_USER)
 			return -EINVAL;
 		break;
+	case AUDIT_FSTYPE:
+		if (entry->rule.listnr != AUDIT_FILTER_FS)
+			return -EINVAL;
+		break;
+	}
+
+	switch(entry->rule.listnr) {
+	case AUDIT_FILTER_FS:
+		switch(f->type) {
+		case AUDIT_FSTYPE:
+		case AUDIT_FILTERKEY:
+			break;
+		default:
+			return -EINVAL;
+		}
 	}
 
 	switch(f->type) {
@@ -391,6 +409,7 @@ static int audit_field_valid(struct audit_entry *entry, struct audit_field *f)
 			return -EINVAL;
 	/* FALL THROUGH */
 	case AUDIT_ARCH:
+	case AUDIT_FSTYPE:
 		if (f->op != Audit_not_equal && f->op != Audit_equal)
 			return -EINVAL;
 		break;
@@ -910,10 +929,13 @@ static inline int audit_add_rule(struct audit_entry *entry)
 #ifdef CONFIG_AUDITSYSCALL
 	int dont_count = 0;
 
-	/* If either of these, don't count towards total */
-	if (entry->rule.listnr == AUDIT_FILTER_USER ||
-		entry->rule.listnr == AUDIT_FILTER_TYPE)
+	/* If any of these, don't count towards total */
+	switch(entry->rule.listnr) {
+	case AUDIT_FILTER_USER:
+	case AUDIT_FILTER_TYPE:
+	case AUDIT_FILTER_FS:
 		dont_count = 1;
+	}
 #endif
 
 	mutex_lock(&audit_filter_mutex);
@@ -989,10 +1011,13 @@ int audit_del_rule(struct audit_entry *entry)
 #ifdef CONFIG_AUDITSYSCALL
 	int dont_count = 0;
 
-	/* If either of these, don't count towards total */
-	if (entry->rule.listnr == AUDIT_FILTER_USER ||
-		entry->rule.listnr == AUDIT_FILTER_TYPE)
+	/* If any of these, don't count towards total */
+	switch(entry->rule.listnr) {
+	case AUDIT_FILTER_USER:
+	case AUDIT_FILTER_TYPE:
+	case AUDIT_FILTER_FS:
 		dont_count = 1;
+	}
 #endif
 
 	mutex_lock(&audit_filter_mutex);
diff --git a/kernel/auditsc.c b/kernel/auditsc.c
index aac1a41f82bd..c9bb29e17335 100644
--- a/kernel/auditsc.c
+++ b/kernel/auditsc.c
@@ -1869,10 +1869,33 @@ void __audit_inode_child(struct inode *parent,
 	struct inode *inode = d_backing_inode(dentry);
 	const char *dname = dentry->d_name.name;
 	struct audit_names *n, *found_parent = NULL, *found_child = NULL;
+	struct audit_entry *e;
+	struct list_head *list = &audit_filter_list[AUDIT_FILTER_FS];
+	int i;
 
 	if (!context->in_syscall)
 		return;
 
+	rcu_read_lock();
+	if (!list_empty(list)) {
+		list_for_each_entry_rcu(e, list, list) {
+			for (i = 0; i < e->rule.field_count; i++) {
+				struct audit_field *f = &e->rule.fields[i];
+
+				if (f->type == AUDIT_FSTYPE) {
+					if (audit_comparator(parent->i_sb->s_magic,
+					    f->op, f->val)) {
+						if (e->rule.action == AUDIT_NEVER) {
+							rcu_read_unlock();
+							return;
+						}
+					}
+				}
+			}
+		}
+	}
+	rcu_read_unlock();
+
 	if (inode)
 		handle_one(inode);