Fix OTP validation in FIPS mode

NSS doesn't allow keys to be loaded directly in FIPS mode. To work around
this, we encrypt the input key using an ephemeral key and then unwrap the
encrypted key.

https://pagure.io/freeipa/issue/7168

Reviewed-By: Rob Crittenden <rcritten@redhat.com>
Reviewed-By: Christian Heimes <cheimes@redhat.com>
Reviewed-By: Rob Crittenden <rcritten@redhat.com>

daemons/ipa-slapi-plugins/libotp/hotp.c

@@ -46,6 +46,7 @@
 #include <time.h>
 
 #include <nss.h>
+#include <blapit.h>
 #include <pk11pub.h>
 #include <hasht.h>
 #include <prnetdb.h>
@@ -66,6 +67,49 @@ static const struct {
     { }
 };
 
+static PK11SymKey *
+import_key(PK11SlotInfo *slot, CK_MECHANISM_TYPE mech, SECItem *key)
+{
+    uint8_t ct[(key->len / AES_BLOCK_SIZE + 1) * AES_BLOCK_SIZE];
+    uint8_t iv[AES_BLOCK_SIZE] = {};
+    SECItem ivitem = { .data = iv, .len = sizeof(iv), .type = siBuffer };
+    SECItem ctitem = { .data = ct, .len = sizeof(ct), .type = siBuffer };
+    PK11SymKey *ekey = NULL;
+    PK11SymKey *skey = NULL;
+
+    /* Try to import the key directly. */
+    skey = PK11_ImportSymKey(slot, mech, PK11_OriginUnwrap,
+                             CKA_SIGN, key, NULL);
+    if (skey)
+        return skey;
+
+    /* If we get here, we are probably in FIPS mode. Let's encrypt the key so
+     * that we can unseal it instead of loading it directly. */
+
+    /* Generate an ephemeral key. */
+    ekey = PK11_TokenKeyGenWithFlags(slot, CKM_AES_CBC_PAD, NULL,
+                                     AES_128_KEY_LENGTH, NULL,
+                                     CKF_ENCRYPT | CKF_UNWRAP,
+                                     PK11_ATTR_SESSION |
+                                     PK11_ATTR_PRIVATE |
+                                     PK11_ATTR_SENSITIVE, NULL);
+    if (!ekey)
+        goto egress;
+
+    /* Encrypt the input key. */
+    if (PK11_Encrypt(ekey, CKM_AES_CBC_PAD, &ivitem, ctitem.data, &ctitem.len,
+                     ctitem.len, key->data, key->len) != SECSuccess)
+        goto egress;
+
+    /* Unwrap the input key. */
+    skey = PK11_UnwrapSymKey(ekey, CKM_AES_CBC_PAD, &ivitem,
+                             &ctitem, mech, CKA_SIGN, key->len);
+
+egress:
+    PK11_FreeSymKey(ekey);
+    return skey;
+}
+
 /*
  * This code is mostly cargo-cult taken from here:
  *   http://www.mozilla.org/projects/security/pki/nss/tech-notes/tn5.html
@@ -90,8 +134,7 @@ static bool hmac(SECItem *key, CK_MECHANISM_TYPE mech, const SECItem *in,
         }
     }
 
-    symkey = PK11_ImportSymKey(slot, mech, PK11_OriginUnwrap,
-                               CKA_SIGN, key, NULL);
+    symkey = import_key(slot, mech, key);
     if (symkey == NULL)
         goto done;