1 files changed, 108 insertions, 0 deletions
diff --git a/crypto/krb5/krb5_api.c b/crypto/krb5/krb5_api.c
index 5c1cd5d07fc3..f6d1bc813daa 100644
--- a/crypto/krb5/krb5_api.c
+++ b/crypto/krb5/krb5_api.c
@@ -40,3 +40,111 @@ const struct krb5_enctype *crypto_krb5_find_enctype(u32 enctype)
 	return NULL;
 }
 EXPORT_SYMBOL(crypto_krb5_find_enctype);
+
+/**
+ * crypto_krb5_how_much_buffer - Work out how much buffer is required for an amount of data
+ * @krb5: The encoding to use.
+ * @mode: The mode in which to operated (checksum/encrypt)
+ * @data_size: How much data we want to allow for
+ * @_offset: Where to place the offset into the buffer
+ *
+ * Calculate how much buffer space is required to wrap a given amount of data.
+ * This allows for a confounder, padding and checksum as appropriate.  The
+ * amount of buffer required is returned and the offset into the buffer at
+ * which the data will start is placed in *_offset.
+ */
+size_t crypto_krb5_how_much_buffer(const struct krb5_enctype *krb5,
+				   enum krb5_crypto_mode mode,
+				   size_t data_size, size_t *_offset)
+{
+	switch (mode) {
+	case KRB5_CHECKSUM_MODE:
+		*_offset = krb5->cksum_len;
+		return krb5->cksum_len + data_size;
+
+	case KRB5_ENCRYPT_MODE:
+		*_offset = krb5->conf_len;
+		return krb5->conf_len + data_size + krb5->cksum_len;
+
+	default:
+		WARN_ON(1);
+		*_offset = 0;
+		return 0;
+	}
+}
+EXPORT_SYMBOL(crypto_krb5_how_much_buffer);
+
+/**
+ * crypto_krb5_how_much_data - Work out how much data can fit in an amount of buffer
+ * @krb5: The encoding to use.
+ * @mode: The mode in which to operated (checksum/encrypt)
+ * @_buffer_size: How much buffer we want to allow for (may be reduced)
+ * @_offset: Where to place the offset into the buffer
+ *
+ * Calculate how much data can be fitted into given amount of buffer.  This
+ * allows for a confounder, padding and checksum as appropriate.  The amount of
+ * data that will fit is returned, the amount of buffer required is shrunk to
+ * allow for alignment and the offset into the buffer at which the data will
+ * start is placed in *_offset.
+ */
+size_t crypto_krb5_how_much_data(const struct krb5_enctype *krb5,
+				 enum krb5_crypto_mode mode,
+				 size_t *_buffer_size, size_t *_offset)
+{
+	size_t buffer_size = *_buffer_size, data_size;
+
+	switch (mode) {
+	case KRB5_CHECKSUM_MODE:
+		if (WARN_ON(buffer_size < krb5->cksum_len + 1))
+			goto bad;
+		*_offset = krb5->cksum_len;
+		return buffer_size - krb5->cksum_len;
+
+	case KRB5_ENCRYPT_MODE:
+		if (WARN_ON(buffer_size < krb5->conf_len + 1 + krb5->cksum_len))
+			goto bad;
+		data_size = buffer_size - krb5->cksum_len;
+		*_offset = krb5->conf_len;
+		return data_size - krb5->conf_len;
+
+	default:
+		WARN_ON(1);
+		goto bad;
+	}
+
+bad:
+	*_offset = 0;
+	return 0;
+}
+EXPORT_SYMBOL(crypto_krb5_how_much_data);
+
+/**
+ * crypto_krb5_where_is_the_data - Find the data in a decrypted message
+ * @krb5: The encoding to use.
+ * @mode: Mode of operation
+ * @_offset: Offset of the secure blob in the buffer; updated to data offset.
+ * @_len: The length of the secure blob; updated to data length.
+ *
+ * Find the offset and size of the data in a secure message so that this
+ * information can be used in the metadata buffer which will get added to the
+ * digest by crypto_krb5_verify_mic().
+ */
+void crypto_krb5_where_is_the_data(const struct krb5_enctype *krb5,
+				   enum krb5_crypto_mode mode,
+				   size_t *_offset, size_t *_len)
+{
+	switch (mode) {
+	case KRB5_CHECKSUM_MODE:
+		*_offset += krb5->cksum_len;
+		*_len -= krb5->cksum_len;
+		return;
+	case KRB5_ENCRYPT_MODE:
+		*_offset += krb5->conf_len;
+		*_len -= krb5->conf_len + krb5->cksum_len;
+		return;
+	default:
+		WARN_ON_ONCE(1);
+		return;
+	}
+}
+EXPORT_SYMBOL(crypto_krb5_where_is_the_data);