1 files changed, 28 insertions, 52 deletions

diff --git a/app/openvpn/src/openvpn/crypto.c b/app/openvpn/src/openvpn/crypto.c
index 62c4ab28..69df29de 100644
--- a/app/openvpn/src/openvpn/crypto.c
+++ b/app/openvpn/src/openvpn/crypto.c
@@ -223,6 +223,30 @@ err:
   return;
 }
 
+int verify_hmac(struct buffer *buf, struct key_ctx *ctx, int offset)
+{
+  uint8_t local_hmac[MAX_HMAC_KEY_LENGTH]; /* HMAC of ciphertext computed locally */
+  int hmac_len = 0;
+
+  hmac_ctx_reset(ctx->hmac);
+  /* Assume the length of the input HMAC */
+  hmac_len = hmac_ctx_size (ctx->hmac);
+
+  /* Authentication fails if insufficient data in packet for HMAC */
+  if (buf->len - offset < hmac_len)
+    return 0;
+
+  hmac_ctx_update (ctx->hmac, BPTR (buf) + hmac_len + offset,
+	BLEN (buf) - hmac_len - offset);
+  hmac_ctx_final (ctx->hmac, local_hmac);
+
+  /* Compare locally computed HMAC with packet HMAC */
+  if (memcmp_constant_time (local_hmac, BPTR (buf) + offset, hmac_len) == 0)
+    return hmac_len;
+
+  return 0;
+}
+
 /*
  * If (opt->flags & CO_USE_IV) is not NULL, we will read an IV from the packet.
  *
@@ -249,25 +273,9 @@ openvpn_decrypt (struct buffer *buf, struct buffer work,
       /* Verify the HMAC */
       if (ctx->hmac)
 	{
-	  int hmac_len;
-	  uint8_t local_hmac[MAX_HMAC_KEY_LENGTH]; /* HMAC of ciphertext computed locally */
-
-	  hmac_ctx_reset(ctx->hmac);
-
-	  /* Assume the length of the input HMAC */
-	  hmac_len = hmac_ctx_size (ctx->hmac);
-
-	  /* Authentication fails if insufficient data in packet for HMAC */
-	  if (buf->len < hmac_len)
-	    CRYPT_ERROR ("missing authentication info");
-
-	  hmac_ctx_update (ctx->hmac, BPTR (buf) + hmac_len, BLEN (buf) - hmac_len);
-	  hmac_ctx_final (ctx->hmac, local_hmac);
-
-	  /* Compare locally computed HMAC with packet HMAC */
-	  if (memcmp_constant_time (local_hmac, BPTR (buf), hmac_len))
+	  int hmac_len = verify_hmac(buf, ctx, 0);
+	  if (hmac_len == 0)
 	    CRYPT_ERROR ("packet HMAC authentication failed");
-
 	  ASSERT (buf_advance (buf, hmac_len));
 	}
 
@@ -399,10 +407,6 @@ openvpn_decrypt (struct buffer *buf, struct buffer work,
 bool
 crypto_test_hmac (struct buffer *buf, const struct crypto_options *opt)
 {
-  struct gc_arena gc;
-  gc_init (&gc);
-  int offset = 4; /* 1 byte opcode + 3 bytes session-id */
-
   if (buf->len > 0 && opt->key_ctx_bi)
     {
       struct key_ctx *ctx = &opt->key_ctx_bi->decrypt;
@@ -410,38 +414,10 @@ crypto_test_hmac (struct buffer *buf, const struct crypto_options *opt)
       /* Verify the HMAC */
       if (ctx->hmac)
 	{
-	  int hmac_len;
-	  uint8_t local_hmac[MAX_HMAC_KEY_LENGTH]; /* HMAC of ciphertext computed locally */
-
-	  hmac_ctx_reset(ctx->hmac);
-
-	  /* Assume the length of the input HMAC */
-	  hmac_len = hmac_ctx_size (ctx->hmac);
-
-	  /* Authentication fails if insufficient data in packet for HMAC */
-	  if ((buf->len - offset) < hmac_len)
-	    {
-	      gc_free (&gc);
-	      return false;
-	    }
-
-	  hmac_ctx_update (ctx->hmac, BPTR (buf) + offset + hmac_len,
-			   BLEN (buf) - offset - hmac_len);
-	  hmac_ctx_final (ctx->hmac, local_hmac);
-
-	  /* Compare locally computed HMAC with packet HMAC */
-	  if (memcmp (local_hmac, BPTR (buf) + offset, hmac_len))
-	    {
-	      gc_free (&gc);
-	      return false;
-	    }
-
-	  gc_free (&gc);
-	  return true;
+	  /* sizeof(uint32_t) comes from peer_id (3 bytes) and opcode (1 byte) */
+	  return verify_hmac(buf, ctx, sizeof(uint32_t)) != 0;
 	}
     }
-
-  gc_free (&gc);
   return false;
 }