[PATCH v8 1/3] lib/asn1_encoder: Add asn1_encode_integer_bytes()

[Jarkko Sakkinen <jarkko@kernel.org>]

Add a helper encoding a positive integer from a byte array in big-endian
format.

Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>
---
 include/linux/asn1_encoder.h |  3 ++
 lib/asn1_encoder.c           | 62 ++++++++++++++++++++++++++++++++++++
 2 files changed, 65 insertions(+)

diff --git a/include/linux/asn1_encoder.h b/include/linux/asn1_encoder.h
index d17484dffb74..e206bd425854 100644
--- a/include/linux/asn1_encoder.h
+++ b/include/linux/asn1_encoder.h
@@ -12,6 +12,9 @@ unsigned char *
 asn1_encode_integer(unsigned char *data, const unsigned char *end_data,
 		    s64 integer);
 unsigned char *
+asn1_encode_integer_bytes(unsigned char *data, const unsigned char *end_data,
+			  const unsigned char *integer, u32 integer_len);
+unsigned char *
 asn1_encode_oid(unsigned char *data, const unsigned char *end_data,
 		u32 oid[], int oid_len);
 unsigned char *
diff --git a/lib/asn1_encoder.c b/lib/asn1_encoder.c
index 92f35aae13b1..22e0acd6fe08 100644
--- a/lib/asn1_encoder.c
+++ b/lib/asn1_encoder.c
@@ -10,6 +10,8 @@
 #include <linux/string.h>
 #include <linux/module.h>
 
+static int asn1_encode_length(unsigned char **data, int *data_len, int len);
+
 /**
  * asn1_encode_integer() - encode positive integer to ASN.1
  * @data:	pointer to the pointer to the data
@@ -85,6 +87,66 @@ asn1_encode_integer(unsigned char *data, const unsigned char *end_data,
 }
 EXPORT_SYMBOL_GPL(asn1_encode_integer);
 
+/**
+ * asn1_encode_integer_bytes() - encode positive integer bytes to ASN.1
+ * @data:		pointer to the pointer to the data
+ * @end_data:		end of data pointer, points one beyond last usable byte in @data
+ * @bytes:		integer bytes
+ * @bytes_len:		amount of bytes
+ *
+ * Encode a positive integer from a byte array in big-endian format. Strip
+ * leading zeros.
+ */
+unsigned char *
+asn1_encode_integer_bytes(unsigned char *data, const unsigned char *end_data,
+			  const unsigned char *bytes, u32 bytes_len)
+{
+	static const unsigned char zero;
+	int data_len = end_data - data;
+	bool add_pad = false;
+	int ret;
+
+	if (IS_ERR(data))
+		return data;
+
+	if (!bytes || !bytes_len)
+		return ERR_PTR(-EINVAL);
+
+	/* Strip leading zeros: */
+	while (bytes_len > 1 && bytes[0] == 0) {
+		bytes++;
+		bytes_len--;
+	}
+
+	if (!bytes_len) {
+		bytes = &zero;
+		bytes_len = 1;
+	} else {
+		add_pad = bytes[0] & 0x80;
+	}
+
+	if (data_len < 2)
+		return ERR_PTR(-EINVAL);
+
+	*(data++) = _tag(UNIV, PRIM, INT);
+	data_len--;
+
+	ret = asn1_encode_length(&data, &data_len, bytes_len + add_pad);
+	if (ret)
+		return ERR_PTR(ret);
+
+	if (data_len < bytes_len + add_pad)
+		return ERR_PTR(-EINVAL);
+
+	if (add_pad)
+		*(data++) = 0;
+
+	memcpy(data, bytes, bytes_len);
+	data += bytes_len;
+	return data;
+}
+EXPORT_SYMBOL_GPL(asn1_encode_integer_bytes);
+
 /* calculate the base 128 digit values setting the top bit of the first octet */
 static int asn1_encode_oid_digit(unsigned char **_data, int *data_len, u32 oid)
 {
-- 
2.47.3