[PATCH ALT4 V3 2/2] audit: filter PATH records keyed on filesystem magic
From: Richard Guy Briggs
Date: Wed Aug 23 2017 - 07:04:20 EST
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@xxxxxxxxxx>
---
v3: rebase
v2: convert AUDIT_FILTER_PATH to AUDIT_FILTER_FS
---
include/uapi/linux/audit.h | 8 ++++++--
kernel/auditfilter.c | 39 ++++++++++++++++++++++++++++++++-------
kernel/auditsc.c | 23 +++++++++++++++++++++++
3 files changed, 61 insertions(+), 9 deletions(-)
diff --git a/include/uapi/linux/audit.h b/include/uapi/linux/audit.h
index 0714a66..be71134 100644
--- a/include/uapi/linux/audit.h
+++ b/include/uapi/linux/audit.h
@@ -155,8 +155,9 @@
#define AUDIT_FILTER_WATCH 0x03 /* Apply rule to file system watches */
#define AUDIT_FILTER_EXIT 0x04 /* Apply rule at syscall exit */
#define AUDIT_FILTER_TYPE 0x05 /* Apply rule at audit_log_start */
+#define AUDIT_FILTER_FS 0x06 /* Apply rule at __audit_inode_child */
-#define AUDIT_NR_FILTERS 6
+#define AUDIT_NR_FILTERS 7
#define AUDIT_FILTER_PREPEND 0x10 /* Prepend to front of list */
@@ -256,6 +257,7 @@
#define AUDIT_OBJ_LEV_HIGH 23
#define AUDIT_LOGINUID_SET 24
#define AUDIT_SESSIONID 25 /* Session ID */
+#define AUDIT_FSTYPE 26 /* FileSystem Type */
/* These are ONLY useful when checking
* at syscall exit time (AUDIT_AT_EXIT). */
@@ -335,13 +337,15 @@ enum {
#define AUDIT_FEATURE_BITMAP_EXCLUDE_EXTEND 0x00000008
#define AUDIT_FEATURE_BITMAP_SESSIONID_FILTER 0x00000010
#define AUDIT_FEATURE_BITMAP_LOST_RESET 0x00000020
+#define AUDIT_FEATURE_BITMAP_FILTER_FS 0x00000040
#define AUDIT_FEATURE_BITMAP_ALL (AUDIT_FEATURE_BITMAP_BACKLOG_LIMIT | \
AUDIT_FEATURE_BITMAP_BACKLOG_WAIT_TIME | \
AUDIT_FEATURE_BITMAP_EXECUTABLE_PATH | \
AUDIT_FEATURE_BITMAP_EXCLUDE_EXTEND | \
AUDIT_FEATURE_BITMAP_SESSIONID_FILTER | \
- AUDIT_FEATURE_BITMAP_LOST_RESET)
+ AUDIT_FEATURE_BITMAP_LOST_RESET | \
+ AUDIT_FEATURE_BITMAP_FILTER_FS)
/* deprecated: AUDIT_VERSION_* */
#define AUDIT_VERSION_LATEST AUDIT_FEATURE_BITMAP_ALL
diff --git a/kernel/auditfilter.c b/kernel/auditfilter.c
index 0b0aa58..4a1758a 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 @@ struct list_head audit_filter_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 int audit_match_signal(struct audit_entry *entry)
#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 11848df..ce6cbda 100644
--- a/kernel/auditsc.c
+++ b/kernel/auditsc.c
@@ -1871,10 +1871,33 @@ 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);
--
1.7.1