Re: [PATCH ALT4 V2 2/2] audit: filter PATH records keyed on filesystem magic

From: Paul Moore
Date: Tue May 30 2017 - 17:30:24 EST

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On Tue, Apr 4, 2017 at 5:21 AM, Richard Guy Briggs <rgb@xxxxxxxxxx> wrote:
> 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_PATH", 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,path -F fstype=0x74726163 -F key=ignore_tracefs
> -a never,path -F fstype=0x64626720 -F key=ignore_debugfs

Trying to look into the future I wonder if we are ever going to need
to expand the "path" filtering to regular inode lookups, e.g.
audit_inode()?

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

Agreed. A good goal whenever possible, but that is a larger topic
beyond the scope of this patchset.

> See: https://github.com/linux-audit/audit-kernel/issues/16
> Test case: https://github.com/linux-audit/audit-testsuite/issues/42
>
> Signed-off-by: Richard Guy Briggs <rgb@xxxxxxxxxx>
> ---
> 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 3c02bb2..0464910 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_PATH 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). */
> @@ -334,12 +336,14 @@ enum {
> #define AUDIT_FEATURE_BITMAP_EXECUTABLE_PATH 0x00000004
> #define AUDIT_FEATURE_BITMAP_SESSIONID_FILTER 0x00000010
> #define AUDIT_FEATURE_BITMAP_LOST_RESET 0x00000020
> +#define AUDIT_FEATURE_BITMAP_FILTER_PATH 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_SESSIONID_FILTER | \
> - AUDIT_FEATURE_BITMAP_LOST_RESET)
> + AUDIT_FEATURE_BITMAP_LOST_RESET | \
> + AUDIT_FEATURE_BITMAP_FILTER_PATH)
>
> /* deprecated: AUDIT_VERSION_* */
> #define AUDIT_VERSION_LATEST AUDIT_FEATURE_BITMAP_ALL
> diff --git a/kernel/auditfilter.c b/kernel/auditfilter.c
> index 239d11c..3e0ccf2 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_PATH:
> ;
> }
> 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_PATH)
> + return -EINVAL;
> + break;
> + }
> +
> + switch(entry->rule.listnr) {
> + case AUDIT_FILTER_PATH:
> + 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_PATH:
> 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_PATH:
> dont_count = 1;
> + }
> #endif
>
> mutex_lock(&audit_filter_mutex);
> diff --git a/kernel/auditsc.c b/kernel/auditsc.c
> index b3797c7..a12531f 100644
> --- a/kernel/auditsc.c
> +++ b/kernel/auditsc.c
> @@ -1868,10 +1868,33 @@ 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_PATH];
> + 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
>
> --
> Linux-audit mailing list
> Linux-audit@xxxxxxxxxx
> https://www.redhat.com/mailman/listinfo/linux-audit

--
paul moore
www.paul-moore.com

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