Smack: Integrate Smack with Audit

Setup the new Audit hooks for Smack. SELinux Audit rule fields are recycled
to avoid `auditd' userspace modifications. Currently only equality testing
is supported on labels acting as a subject (AUDIT_SUBJ_USER) or as an object
(AUDIT_OBJ_USER).

Signed-off-by: Ahmed S. Darwish <darwish.07@gmail.com>
Acked-by: Casey Schaufler <casey@schaufler-ca.com>

1 files changed, 155 insertions, 0 deletions

diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c
index 92baee53a7dc..fe0ae1bf1650 100644
--- a/security/smack/smack_lsm.c
+++ b/security/smack/smack_lsm.c
@@ -26,6 +26,7 @@
 #include <linux/pipe_fs_i.h>
 #include <net/netlabel.h>
 #include <net/cipso_ipv4.h>
+#include <linux/audit.h>
 
 #include "smack.h"
 
@@ -752,6 +753,18 @@ static int smack_inode_listsecurity(struct inode *inode, char *buffer,
         return -EINVAL;
 }
 
+/**
+ * smack_inode_getsecid - Extract inode's security id
+ * @inode: inode to extract the info from
+ * @secid: where result will be saved
+ */
+static void smack_inode_getsecid(const struct inode *inode, u32 *secid)
+{
+        struct inode_smack *isp = inode->i_security;
+
+        *secid = smack_to_secid(isp->smk_inode);
+}
+
 /*
  * File Hooks
  */
@@ -1805,6 +1818,18 @@ static int smack_ipc_permission(struct kern_ipc_perm *ipp, short flag)
         return smk_curacc(isp, may);
 }
 
+/**
+ * smack_ipc_getsecid - Extract smack security id
+ * @ipcp: the object permissions
+ * @secid: where result will be saved
+ */
+static void smack_ipc_getsecid(struct kern_ipc_perm *ipp, u32 *secid)
+{
+        char *smack = ipp->security;
+
+        *secid = smack_to_secid(smack);
+}
+
 /* module stacking operations */
 
 /**
@@ -2382,6 +2407,124 @@ static int smack_key_permission(key_ref_t key_ref,
 #endif /* CONFIG_KEYS */
 
 /*
+ * Smack Audit hooks
+ *
+ * Audit requires a unique representation of each Smack specific
+ * rule. This unique representation is used to distinguish the
+ * object to be audited from remaining kernel objects and also
+ * works as a glue between the audit hooks.
+ *
+ * Since repository entries are added but never deleted, we'll use
+ * the smack_known label address related to the given audit rule as
+ * the needed unique representation. This also better fits the smack
+ * model where nearly everything is a label.
+ */
+#ifdef CONFIG_AUDIT
+
+/**
+ * smack_audit_rule_init - Initialize a smack audit rule
+ * @field: audit rule fields given from user-space (audit.h)
+ * @op: required testing operator (=, !=, >, <, ...)
+ * @rulestr: smack label to be audited
+ * @vrule: pointer to save our own audit rule representation
+ *
+ * Prepare to audit cases where (@field @op @rulestr) is true.
+ * The label to be audited is created if necessay.
+ */
+static int smack_audit_rule_init(u32 field, u32 op, char *rulestr, void **vrule)
+{
+        char **rule = (char **)vrule;
+        *rule = NULL;
+
+        if (field != AUDIT_SUBJ_USER && field != AUDIT_OBJ_USER)
+                return -EINVAL;
+
+        if (op != AUDIT_EQUAL && op != AUDIT_NOT_EQUAL)
+                return -EINVAL;
+
+        *rule = smk_import(rulestr, 0);
+
+        return 0;
+}
+
+/**
+ * smack_audit_rule_known - Distinguish Smack audit rules
+ * @krule: rule of interest, in Audit kernel representation format
+ *
+ * This is used to filter Smack rules from remaining Audit ones.
+ * If it's proved that this rule belongs to us, the
+ * audit_rule_match hook will be called to do the final judgement.
+ */
+static int smack_audit_rule_known(struct audit_krule *krule)
+{
+        struct audit_field *f;
+        int i;
+
+        for (i = 0; i < krule->field_count; i++) {
+                f = &krule->fields[i];
+
+                if (f->type == AUDIT_SUBJ_USER || f->type == AUDIT_OBJ_USER)
+                        return 1;
+        }
+
+        return 0;
+}
+
+/**
+ * smack_audit_rule_match - Audit given object ?
+ * @secid: security id for identifying the object to test
+ * @field: audit rule flags given from user-space
+ * @op: required testing operator
+ * @vrule: smack internal rule presentation
+ * @actx: audit context associated with the check
+ *
+ * The core Audit hook. It's used to take the decision of
+ * whether to audit or not to audit a given object.
+ */
+static int smack_audit_rule_match(u32 secid, u32 field, u32 op, void *vrule,
+                                  struct audit_context *actx)
+{
+        char *smack;
+        char *rule = vrule;
+
+        if (!rule) {
+                audit_log(actx, GFP_KERNEL, AUDIT_SELINUX_ERR,
+                          "Smack: missing rule\n");
+                return -ENOENT;
+        }
+
+        if (field != AUDIT_SUBJ_USER && field != AUDIT_OBJ_USER)
+                return 0;
+
+        smack = smack_from_secid(secid);
+
+        /*
+         * No need to do string comparisons. If a match occurs,
+         * both pointers will point to the same smack_known
+         * label.
+         */
+        if (op == AUDIT_EQUAL)
+                return (rule == smack);
+        if (op == AUDIT_NOT_EQUAL)
+                return (rule != smack);
+
+        return 0;
+}
+
+/**
+ * smack_audit_rule_free - free smack rule representation
+ * @vrule: rule to be freed.
+ *
+ * No memory was allocated.
+ */
+static void smack_audit_rule_free(void *vrule)
+{
+        /* No-op */
+}
+
+#endif /* CONFIG_AUDIT */
+
+/*
  * smack_secid_to_secctx - return the smack label for a secid
  * @secid: incoming integer
  * @secdata: destination
@@ -2467,6 +2610,7 @@ struct security_operations smack_ops = {
         .inode_getsecurity =            smack_inode_getsecurity,
         .inode_setsecurity =            smack_inode_setsecurity,
         .inode_listsecurity =           smack_inode_listsecurity,
+        .inode_getsecid =               smack_inode_getsecid,
 
         .file_permission =              smack_file_permission,
         .file_alloc_security =          smack_file_alloc_security,
@@ -2498,6 +2642,7 @@ struct security_operations smack_ops = {
         .task_prctl =                   cap_task_prctl,
 
         .ipc_permission =               smack_ipc_permission,
+        .ipc_getsecid =                 smack_ipc_getsecid,
 
         .msg_msg_alloc_security =       smack_msg_msg_alloc_security,
         .msg_msg_free_security =        smack_msg_msg_free_security,
@@ -2542,12 +2687,22 @@ struct security_operations smack_ops = {
         .sk_free_security =             smack_sk_free_security,
         .sock_graft =                   smack_sock_graft,
         .inet_conn_request =            smack_inet_conn_request,
+
  /* key management security hooks */
 #ifdef CONFIG_KEYS
         .key_alloc =                    smack_key_alloc,
         .key_free =                     smack_key_free,
         .key_permission =               smack_key_permission,
 #endif /* CONFIG_KEYS */
+
+ /* Audit hooks */
+#ifdef CONFIG_AUDIT
+        .audit_rule_init =              smack_audit_rule_init,
+        .audit_rule_known =             smack_audit_rule_known,
+        .audit_rule_match =             smack_audit_rule_match,
+        .audit_rule_free =              smack_audit_rule_free,
+#endif /* CONFIG_AUDIT */
+
         .secid_to_secctx =              smack_secid_to_secctx,
         .secctx_to_secid =              smack_secctx_to_secid,
         .release_secctx =               smack_release_secctx,