Re: [PATCH ALT4 V2 2/2] 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_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

Test case: https://github.com/linux-audit/audit-testsuite/issues/42 Signed-off-by: Richard Guy Briggs <rgb(a)redhat.com&gt; --- 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