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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>
This commit is contained in:
Richard Guy Briggs 2017-08-23 07:03:39 -04:00 committed by Paul Moore
parent f7b53637c0
commit 42d5e37654
3 changed files with 61 additions and 9 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

8
include/uapi/linux/audit.h
View File

@ -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

39
kernel/auditfilter.c
View File

@ -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);

23
kernel/auditsc.c
View File

@ -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);