[PATCH] add rule filterkey

Add support for a rule key, which can be used to tie audit records to audit
rules.  This is useful when a watched file is accessed through a link or
symlink, as well as for general audit log analysis.

Because this patch uses a string key instead of an integer key, there is a bit
of extra overhead to do the kstrdup() when a rule fires.  However, we're also
allocating memory for the audit record buffer, so it's probably not that
significant.  I went ahead with a string key because it seems more
user-friendly.

Note that the user must ensure that filterkeys are unique.  The kernel only
checks for duplicate rules.

Signed-off-by: Amy Griffis <amy.griffis@hpd.com>

4 files changed, 78 insertions, 36 deletions

diff --git a/include/linux/audit.h b/include/linux/audit.h
index e051ff9c5b50..a489104ae3a4 100644
--- a/include/linux/audit.h
+++ b/include/linux/audit.h
@@ -122,6 +122,7 @@
 /* Rule structure sizes -- if these change, different AUDIT_ADD and
  * AUDIT_LIST commands must be implemented. */
 #define AUDIT_MAX_FIELDS   64
+#define AUDIT_MAX_KEY_LEN  32
 #define AUDIT_BITMASK_SIZE 64
 #define AUDIT_WORD(nr) ((__u32)((nr)/32))
 #define AUDIT_BIT(nr)  (1 << ((nr) - AUDIT_WORD(nr)*32))
@@ -171,6 +172,8 @@
 #define AUDIT_ARG2      (AUDIT_ARG0+2)
 #define AUDIT_ARG3      (AUDIT_ARG0+3)
 
+#define AUDIT_FILTERKEY 210
+
 #define AUDIT_NEGATE                    0x80000000
 
 /* These are the supported operators.
diff --git a/kernel/audit.h b/kernel/audit.h
index 8323e4132a33..6aa33b848cf2 100644
--- a/kernel/audit.h
+++ b/kernel/audit.h
@@ -81,6 +81,7 @@ struct audit_krule {
         u32                     mask[AUDIT_BITMASK_SIZE];
         u32                     buflen; /* for data alloc on list rules */
         u32                     field_count;
+        char                    *filterkey; /* ties events to rules */
         struct audit_field      *fields;
         struct audit_field      *inode_f; /* quick access to an inode field */
         struct audit_watch      *watch; /* associated watch */
diff --git a/kernel/auditfilter.c b/kernel/auditfilter.c
index 4c99d2c586ed..e98db08fc6df 100644
--- a/kernel/auditfilter.c
+++ b/kernel/auditfilter.c
@@ -141,6 +141,7 @@ static inline void audit_free_rule(struct audit_entry *e)
                         selinux_audit_rule_free(f->se_rule);
                 }
         kfree(e->rule.fields);
+        kfree(e->rule.filterkey);
         kfree(e);
 }
 
@@ -511,6 +512,16 @@ static struct audit_entry *audit_data_to_entry(struct audit_rule_data *data,
                         if (err)
                                 goto exit_free;
                         break;
+                case AUDIT_FILTERKEY:
+                        err = -EINVAL;
+                        if (entry->rule.filterkey || f->val > AUDIT_MAX_KEY_LEN)
+                                goto exit_free;
+                        str = audit_unpack_string(&bufp, &remain, f->val);
+                        if (IS_ERR(str))
+                                goto exit_free;
+                        entry->rule.buflen += f->val;
+                        entry->rule.filterkey = str;
+                        break;
                 default:
                         goto exit_free;
                 }
@@ -612,6 +623,10 @@ static struct audit_rule_data *audit_krule_to_data(struct audit_krule *krule)
                         data->buflen += data->values[i] =
                                 audit_pack_string(&bufp, krule->watch->path);
                         break;
+                case AUDIT_FILTERKEY:
+                        data->buflen += data->values[i] =
+                                audit_pack_string(&bufp, krule->filterkey);
+                        break;
                 default:
                         data->values[i] = f->val;
                 }
@@ -651,6 +666,11 @@ static int audit_compare_rule(struct audit_krule *a, struct audit_krule *b)
                         if (strcmp(a->watch->path, b->watch->path))
                                 return 1;
                         break;
+                case AUDIT_FILTERKEY:
+                        /* both filterkeys exist based on above type compare */
+                        if (strcmp(a->filterkey, b->filterkey))
+                                return 1;
+                        break;
                 default:
                         if (a->fields[i].val != b->fields[i].val)
                                 return 1;
@@ -730,6 +750,7 @@ static struct audit_entry *audit_dupe_rule(struct audit_krule *old,
         u32 fcount = old->field_count;
         struct audit_entry *entry;
         struct audit_krule *new;
+        char *fk;
         int i, err = 0;
 
         entry = audit_init_entry(fcount);
@@ -760,6 +781,13 @@ static struct audit_entry *audit_dupe_rule(struct audit_krule *old,
                 case AUDIT_SE_CLR:
                         err = audit_dupe_selinux_field(&new->fields[i],
                                                        &old->fields[i]);
+                        break;
+                case AUDIT_FILTERKEY:
+                        fk = kstrdup(old->filterkey, GFP_KERNEL);
+                        if (unlikely(!fk))
+                                err = -ENOMEM;
+                        else
+                                new->filterkey = fk;
                 }
                 if (err) {
                         audit_free_rule(entry);
@@ -1245,6 +1273,34 @@ static void audit_list_rules(int pid, int seq, struct sk_buff_head *q)
                 skb_queue_tail(q, skb);
 }
 
+/* Log rule additions and removals */
+static void audit_log_rule_change(uid_t loginuid, u32 sid, char *action,
+                                  struct audit_krule *rule, int res)
+{
+        struct audit_buffer *ab;
+
+        ab = audit_log_start(NULL, GFP_KERNEL, AUDIT_CONFIG_CHANGE);
+        if (!ab)
+                return;
+        audit_log_format(ab, "auid=%u", loginuid);
+        if (sid) {
+                char *ctx = NULL;
+                u32 len;
+                if (selinux_ctxid_to_string(sid, &ctx, &len))
+                        audit_log_format(ab, " ssid=%u", sid);
+                else
+                        audit_log_format(ab, " subj=%s", ctx);
+                kfree(ctx);
+        }
+        audit_log_format(ab, " %s rule key=", action);
+        if (rule->filterkey)
+                audit_log_untrustedstring(ab, rule->filterkey);
+        else
+                audit_log_format(ab, "(null)");
+        audit_log_format(ab, " list=%d res=%d", rule->listnr, res);
+        audit_log_end(ab);
+}
+
 /**
  * audit_receive_filter - apply all rules to the specified message type
  * @type: audit message type
@@ -1304,24 +1360,7 @@ int audit_receive_filter(int type, int pid, int uid, int seq, void *data,
 
                 err = audit_add_rule(entry,
                                      &audit_filter_list[entry->rule.listnr]);
-
-                if (sid) {
-                        char *ctx = NULL;
-                        u32 len;
-                        if (selinux_ctxid_to_string(sid, &ctx, &len)) {
-                                /* Maybe call audit_panic? */
-                                audit_log(NULL, GFP_KERNEL, AUDIT_CONFIG_CHANGE,
-                                 "auid=%u ssid=%u add rule to list=%d res=%d",
-                                 loginuid, sid, entry->rule.listnr, !err);
-                        } else
-                                audit_log(NULL, GFP_KERNEL, AUDIT_CONFIG_CHANGE,
-                                 "auid=%u subj=%s add rule to list=%d res=%d",
-                                 loginuid, ctx, entry->rule.listnr, !err);
-                        kfree(ctx);
-                } else
-                        audit_log(NULL, GFP_KERNEL, AUDIT_CONFIG_CHANGE,
-                                "auid=%u add rule to list=%d res=%d",
-                                loginuid, entry->rule.listnr, !err);
+                audit_log_rule_change(loginuid, sid, "add", &entry->rule, !err);
 
                 if (err)
                         audit_free_rule(entry);
@@ -1337,24 +1376,8 @@ int audit_receive_filter(int type, int pid, int uid, int seq, void *data,
 
                 err = audit_del_rule(entry,
                                      &audit_filter_list[entry->rule.listnr]);
-
-                if (sid) {
-                        char *ctx = NULL;
-                        u32 len;
-                        if (selinux_ctxid_to_string(sid, &ctx, &len)) {
-                                /* Maybe call audit_panic? */
-                                audit_log(NULL, GFP_KERNEL, AUDIT_CONFIG_CHANGE,
-                                        "auid=%u ssid=%u remove rule from list=%d res=%d",
-                                         loginuid, sid, entry->rule.listnr, !err);
-                        } else
-                                audit_log(NULL, GFP_KERNEL, AUDIT_CONFIG_CHANGE,
-                                        "auid=%u subj=%s remove rule from list=%d res=%d",
-                                         loginuid, ctx, entry->rule.listnr, !err);
-                        kfree(ctx);
-                } else
-                        audit_log(NULL, GFP_KERNEL, AUDIT_CONFIG_CHANGE,
-                                "auid=%u remove rule from list=%d res=%d",
-                                loginuid, entry->rule.listnr, !err);
+                audit_log_rule_change(loginuid, sid, "remove", &entry->rule,
+                                      !err);
 
                 audit_free_rule(entry);
                 break;
diff --git a/kernel/auditsc.c b/kernel/auditsc.c
index dc5e3f01efe7..316657855165 100644
--- a/kernel/auditsc.c
+++ b/kernel/auditsc.c
@@ -186,6 +186,7 @@ struct audit_context {
         int                 auditable;  /* 1 if record should be written */
         int                 name_count;
         struct audit_names  names[AUDIT_NAMES];
+        char *              filterkey;  /* key for rule that triggered record */
         struct dentry *     pwd;
         struct vfsmount *   pwdmnt;
         struct audit_context *previous; /* For nested syscalls */
@@ -348,11 +349,17 @@ static int audit_filter_rules(struct task_struct *tsk,
                         if (ctx)
                                 result = audit_comparator(ctx->argv[f->type-AUDIT_ARG0], f->op, f->val);
                         break;
+                case AUDIT_FILTERKEY:
+                        /* ignore this field for filtering */
+                        result = 1;
+                        break;
                 }
 
                 if (!result)
                         return 0;
         }
+        if (rule->filterkey)
+                ctx->filterkey = kstrdup(rule->filterkey, GFP_ATOMIC);
         switch (rule->action) {
         case AUDIT_NEVER:    *state = AUDIT_DISABLED;       break;
         case AUDIT_ALWAYS:   *state = AUDIT_RECORD_CONTEXT; break;
@@ -627,6 +634,7 @@ static inline void audit_free_context(struct audit_context *context)
                 }
                 audit_free_names(context);
                 audit_free_aux(context);
+                kfree(context->filterkey);
                 kfree(context);
                 context  = previous;
         } while (context);
@@ -735,6 +743,11 @@ static void audit_log_exit(struct audit_context *context, struct task_struct *ts
                   context->euid, context->suid, context->fsuid,
                   context->egid, context->sgid, context->fsgid, tty);
         audit_log_task_info(ab, tsk);
+        if (context->filterkey) {
+                audit_log_format(ab, " key=");
+                audit_log_untrustedstring(ab, context->filterkey);
+        } else
+                audit_log_format(ab, " key=(null)");
         audit_log_end(ab);
 
         for (aux = context->aux; aux; aux = aux->next) {
@@ -1060,6 +1073,8 @@ void audit_syscall_exit(int valid, long return_code)
         } else {
                 audit_free_names(context);
                 audit_free_aux(context);
+                kfree(context->filterkey);
+                context->filterkey = NULL;
                 tsk->audit_context = context;
         }
 }