Smack: Privilege check on key operations

Smack: Privilege check on key operations Operations on key objects are subjected to Smack policy even if the process is privileged. This is inconsistent with the general behavior of Smack and may cause issues with authentication by privileged daemons. This patch allows processes with CAP_MAC_OVERRIDE to access keys even if the Smack rules indicate otherwise. Reported-by: Jose Bollo <[email protected]> Signed-off-by: Casey Schaufler <[email protected]>
johnjwang · Jan 10, 2018 · d19dfe5 · d19dfe5
1 parent da49b5d
commit d19dfe5
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Showing 3 changed files with 34 additions and 11 deletions.
diff --git a/security/smack/smack.h b/security/smack/smack.h
@@ -321,6 +321,7 @@ struct smack_known *smk_import_entry(const char *, int);
 void smk_insert_entry(struct smack_known *skp);
 struct smack_known *smk_find_entry(const char *);
 bool smack_privileged(int cap);
+bool smack_privileged_cred(int cap, const struct cred *cred);
 void smk_destroy_label_list(struct list_head *list);
 
 /*

diff --git a/security/smack/smack_access.c b/security/smack/smack_access.c
@@ -623,26 +623,24 @@ struct smack_known *smack_from_secid(const u32 secid)
 LIST_HEAD(smack_onlycap_list);
 DEFINE_MUTEX(smack_onlycap_lock);
 
-/*
+/**
+ * smack_privileged_cred - are all privilege requirements met by cred
+ * @cap: The requested capability
+ * @cred: the credential to use
+ *
  * Is the task privileged and allowed to be privileged
  * by the onlycap rule.
  *
  * Returns true if the task is allowed to be privileged, false if it's not.
  */
-bool smack_privileged(int cap)
+bool smack_privileged_cred(int cap, const struct cred *cred)
 {
-	struct smack_known *skp = smk_of_current();
+	struct task_smack *tsp = cred->security;
+	struct smack_known *skp = tsp->smk_task;
 	struct smack_known_list_elem *sklep;
 	int rc;
 
-	/*
-	 * All kernel tasks are privileged
-	 */
-	if (unlikely(current->flags & PF_KTHREAD))
-		return true;
-
-	rc = cap_capable(current_cred(), &init_user_ns, cap,
-				SECURITY_CAP_AUDIT);
+	rc = cap_capable(cred, &init_user_ns, cap, SECURITY_CAP_AUDIT);
 	if (rc)
 		return false;
 
@@ -662,3 +660,23 @@ bool smack_privileged(int cap)
 
 	return false;
 }
+
+/**
+ * smack_privileged - are all privilege requirements met
+ * @cap: The requested capability
+ *
+ * Is the task privileged and allowed to be privileged
+ * by the onlycap rule.
+ *
+ * Returns true if the task is allowed to be privileged, false if it's not.
+ */
+bool smack_privileged(int cap)
+{
+	/*
+	 * All kernel tasks are privileged
+	 */
+	if (unlikely(current->flags & PF_KTHREAD))
+		return true;
+
+	return smack_privileged_cred(cap, current_cred());
+}
diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c
@@ -4369,6 +4369,10 @@ static int smack_key_permission(key_ref_t key_ref,
 	 */
 	if (tkp == NULL)
 		return -EACCES;
+
+	if (smack_privileged_cred(CAP_MAC_OVERRIDE, cred))
+		return 0;
+
 #ifdef CONFIG_AUDIT
 	smk_ad_init(&ad, __func__, LSM_AUDIT_DATA_KEY);
 	ad.a.u.key_struct.key = keyp->serial;