[PATCH] support for context based audit filtering

The following patch provides selinux interfaces that will allow the audit
system to perform filtering based on the process context (user, role, type,
sensitivity, and clearance).  These interfaces will allow the selinux
module to perform efficient matches based on lower level selinux constructs,
rather than relying on context retrievals and string comparisons within
the audit module.  It also allows for dominance checks on the mls portion
of the contexts that are impossible with only string comparisons.

Signed-off-by: Darrel Goeddel <dgoeddel@trustedcs.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

3 files changed, 266 insertions, 3 deletions

diff --git a/security/selinux/ss/mls.c b/security/selinux/ss/mls.c
index 84047f69f9c1..7bc5b6440f70 100644
--- a/security/selinux/ss/mls.c
+++ b/security/selinux/ss/mls.c
@@ -8,7 +8,7 @@
  *
  *      Support for enhanced MLS infrastructure.
  *
- * Copyright (C) 2004-2005 Trusted Computer Solutions, Inc.
+ * Copyright (C) 2004-2006 Trusted Computer Solutions, Inc.
  */
 
 #include <linux/kernel.h>
@@ -385,6 +385,34 @@ out:
 }
 
 /*
+ * Set the MLS fields in the security context structure
+ * `context' based on the string representation in
+ * the string `str'.  This function will allocate temporary memory with the
+ * given constraints of gfp_mask.
+ */
+int mls_from_string(char *str, struct context *context, gfp_t gfp_mask)
+{
+        char *tmpstr, *freestr;
+        int rc;
+
+        if (!selinux_mls_enabled)
+                return -EINVAL;
+
+        /* we need freestr because mls_context_to_sid will change
+           the value of tmpstr */
+        tmpstr = freestr = kstrdup(str, gfp_mask);
+        if (!tmpstr) {
+                rc = -ENOMEM;
+        } else {
+                rc = mls_context_to_sid(':', &tmpstr, context,
+                                        NULL, SECSID_NULL);
+                kfree(freestr);
+        }
+
+        return rc;
+}
+
+/*
  * Copies the effective MLS range from `src' into `dst'.
  */
 static inline int mls_scopy_context(struct context *dst,
diff --git a/security/selinux/ss/mls.h b/security/selinux/ss/mls.h
index 03de697c8058..fbb42f07dd7c 100644
--- a/security/selinux/ss/mls.h
+++ b/security/selinux/ss/mls.h
@@ -8,7 +8,7 @@
  *
  *      Support for enhanced MLS infrastructure.
  *
- * Copyright (C) 2004-2005 Trusted Computer Solutions, Inc.
+ * Copyright (C) 2004-2006 Trusted Computer Solutions, Inc.
  */
 
 #ifndef _SS_MLS_H_
@@ -27,6 +27,8 @@ int mls_context_to_sid(char oldc,
                        struct sidtab *s,
                        u32 def_sid);
 
+int mls_from_string(char *str, struct context *context, gfp_t gfp_mask);
+
 int mls_convert_context(struct policydb *oldp,
                         struct policydb *newp,
                         struct context *context);
diff --git a/security/selinux/ss/services.c b/security/selinux/ss/services.c
index 61492485de84..7177e98df7f3 100644
--- a/security/selinux/ss/services.c
+++ b/security/selinux/ss/services.c
@@ -7,12 +7,13 @@
  * Updated: Trusted Computer Solutions, Inc. <dgoeddel@trustedcs.com>
  *
  *      Support for enhanced MLS infrastructure.
+ *      Support for context based audit filters.
  *
  * Updated: Frank Mayer <mayerf@tresys.com> and Karl MacMillan <kmacmillan@tresys.com>
  *
  *      Added conditional policy language extensions
  *
- * Copyright (C) 2004-2005 Trusted Computer Solutions, Inc.
+ * Copyright (C) 2004-2006 Trusted Computer Solutions, Inc.
  * Copyright (C) 2003 - 2004 Tresys Technology, LLC
  * Copyright (C) 2003 Red Hat, Inc., James Morris <jmorris@redhat.com>
  *      This program is free software; you can redistribute it and/or modify
@@ -1811,3 +1812,235 @@ out:
         POLICY_RDUNLOCK;
         return rc;
 }
+
+struct selinux_audit_rule {
+        u32 au_seqno;
+        struct context au_ctxt;
+};
+
+void selinux_audit_rule_free(struct selinux_audit_rule *rule)
+{
+        if (rule) {
+                context_destroy(&rule->au_ctxt);
+                kfree(rule);
+        }
+}
+
+int selinux_audit_rule_init(u32 field, u32 op, char *rulestr,
+                            struct selinux_audit_rule **rule)
+{
+        struct selinux_audit_rule *tmprule;
+        struct role_datum *roledatum;
+        struct type_datum *typedatum;
+        struct user_datum *userdatum;
+        int rc = 0;
+
+        *rule = NULL;
+
+        if (!ss_initialized)
+                return -ENOTSUPP;
+
+        switch (field) {
+        case AUDIT_SE_USER:
+        case AUDIT_SE_ROLE:
+        case AUDIT_SE_TYPE:
+                /* only 'equals' and 'not equals' fit user, role, and type */
+                if (op != AUDIT_EQUAL && op != AUDIT_NOT_EQUAL)
+                        return -EINVAL;
+                break;
+        case AUDIT_SE_SEN:
+        case AUDIT_SE_CLR:
+                /* we do not allow a range, indicated by the presense of '-' */
+                if (strchr(rulestr, '-'))
+                        return -EINVAL;
+                break;
+        default:
+                /* only the above fields are valid */
+                return -EINVAL;
+        }
+
+        tmprule = kzalloc(sizeof(struct selinux_audit_rule), GFP_KERNEL);
+        if (!tmprule)
+                return -ENOMEM;
+
+        context_init(&tmprule->au_ctxt);
+
+        POLICY_RDLOCK;
+
+        tmprule->au_seqno = latest_granting;
+
+        switch (field) {
+        case AUDIT_SE_USER:
+                userdatum = hashtab_search(policydb.p_users.table, rulestr);
+                if (!userdatum)
+                        rc = -EINVAL;
+                else
+                        tmprule->au_ctxt.user = userdatum->value;
+                break;
+        case AUDIT_SE_ROLE:
+                roledatum = hashtab_search(policydb.p_roles.table, rulestr);
+                if (!roledatum)
+                        rc = -EINVAL;
+                else
+                        tmprule->au_ctxt.role = roledatum->value;
+                break;
+        case AUDIT_SE_TYPE:
+                typedatum = hashtab_search(policydb.p_types.table, rulestr);
+                if (!typedatum)
+                        rc = -EINVAL;
+                else
+                        tmprule->au_ctxt.type = typedatum->value;
+                break;
+        case AUDIT_SE_SEN:
+        case AUDIT_SE_CLR:
+                rc = mls_from_string(rulestr, &tmprule->au_ctxt, GFP_ATOMIC);
+                break;
+        }
+
+        POLICY_RDUNLOCK;
+
+        if (rc) {
+                selinux_audit_rule_free(tmprule);
+                tmprule = NULL;
+        }
+
+        *rule = tmprule;
+
+        return rc;
+}
+
+int selinux_audit_rule_match(u32 ctxid, u32 field, u32 op,
+                             struct selinux_audit_rule *rule,
+                             struct audit_context *actx)
+{
+        struct context *ctxt;
+        struct mls_level *level;
+        int match = 0;
+
+        if (!rule) {
+                audit_log(actx, GFP_ATOMIC, AUDIT_SELINUX_ERR,
+                          "selinux_audit_rule_match: missing rule\n");
+                return -ENOENT;
+        }
+
+        POLICY_RDLOCK;
+
+        if (rule->au_seqno < latest_granting) {
+                audit_log(actx, GFP_ATOMIC, AUDIT_SELINUX_ERR,
+                          "selinux_audit_rule_match: stale rule\n");
+                match = -ESTALE;
+                goto out;
+        }
+
+        ctxt = sidtab_search(&sidtab, ctxid);
+        if (!ctxt) {
+                audit_log(actx, GFP_ATOMIC, AUDIT_SELINUX_ERR,
+                          "selinux_audit_rule_match: unrecognized SID %d\n",
+                          ctxid);
+                match = -ENOENT;
+                goto out;
+        }
+
+        /* a field/op pair that is not caught here will simply fall through
+           without a match */
+        switch (field) {
+        case AUDIT_SE_USER:
+                switch (op) {
+                case AUDIT_EQUAL:
+                        match = (ctxt->user == rule->au_ctxt.user);
+                        break;
+                case AUDIT_NOT_EQUAL:
+                        match = (ctxt->user != rule->au_ctxt.user);
+                        break;
+                }
+                break;
+        case AUDIT_SE_ROLE:
+                switch (op) {
+                case AUDIT_EQUAL:
+                        match = (ctxt->role == rule->au_ctxt.role);
+                        break;
+                case AUDIT_NOT_EQUAL:
+                        match = (ctxt->role != rule->au_ctxt.role);
+                        break;
+                }
+                break;
+        case AUDIT_SE_TYPE:
+                switch (op) {
+                case AUDIT_EQUAL:
+                        match = (ctxt->type == rule->au_ctxt.type);
+                        break;
+                case AUDIT_NOT_EQUAL:
+                        match = (ctxt->type != rule->au_ctxt.type);
+                        break;
+                }
+                break;
+        case AUDIT_SE_SEN:
+        case AUDIT_SE_CLR:
+                level = (op == AUDIT_SE_SEN ?
+                         &ctxt->range.level[0] : &ctxt->range.level[1]);
+                switch (op) {
+                case AUDIT_EQUAL:
+                        match = mls_level_eq(&rule->au_ctxt.range.level[0],
+                                             level);
+                        break;
+                case AUDIT_NOT_EQUAL:
+                        match = !mls_level_eq(&rule->au_ctxt.range.level[0],
+                                              level);
+                        break;
+                case AUDIT_LESS_THAN:
+                        match = (mls_level_dom(&rule->au_ctxt.range.level[0],
+                                               level) &&
+                                 !mls_level_eq(&rule->au_ctxt.range.level[0],
+                                               level));
+                        break;
+                case AUDIT_LESS_THAN_OR_EQUAL:
+                        match = mls_level_dom(&rule->au_ctxt.range.level[0],
+                                              level);
+                        break;
+                case AUDIT_GREATER_THAN:
+                        match = (mls_level_dom(level,
+                                              &rule->au_ctxt.range.level[0]) &&
+                                 !mls_level_eq(level,
+                                               &rule->au_ctxt.range.level[0]));
+                        break;
+                case AUDIT_GREATER_THAN_OR_EQUAL:
+                        match = mls_level_dom(level,
+                                              &rule->au_ctxt.range.level[0]);
+                        break;
+                }
+        }
+
+out:
+        POLICY_RDUNLOCK;
+        return match;
+}
+
+static int (*aurule_callback)(void) = NULL;
+
+static int aurule_avc_callback(u32 event, u32 ssid, u32 tsid,
+                               u16 class, u32 perms, u32 *retained)
+{
+        int err = 0;
+
+        if (event == AVC_CALLBACK_RESET && aurule_callback)
+                err = aurule_callback();
+        return err;
+}
+
+static int __init aurule_init(void)
+{
+        int err;
+
+        err = avc_add_callback(aurule_avc_callback, AVC_CALLBACK_RESET,
+                               SECSID_NULL, SECSID_NULL, SECCLASS_NULL, 0);
+        if (err)
+                panic("avc_add_callback() failed, error %d\n", err);
+
+        return err;
+}
+__initcall(aurule_init);
+
+void selinux_audit_set_callback(int (*callback)(void))
+{
+        aurule_callback = callback;
+}