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

[Richard Guy Briggs]

On 2017-04-04 05:21, Richard Guy Briggs 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
> 
> 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

Sorry, this issue number is wrong.
See: https://github.com/linux-audit/audit-kernel/issues/8

> 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
> 

- RGB

--
Richard Guy Briggs <rgb@xxxxxxxxxx>
Sr. S/W Engineer, Kernel Security, Base Operating Systems
Remote, Ottawa, Red Hat Canada
IRC: rgb, SunRaycer
Voice: +1.647.777.2635, Internal: (81) 32635