Quelle asn1_encoder.c Sprache: C

// SPDX-License-Identifier: GPL-2.0-only
/*
* Simple encoder primitives for ASN.1 BER/DER/CER
*
* Copyright (C) 2019 James.Bottomley@HansenPartnership.com
*/

#include <linux/asn1_encoder.h>
#include <linux/bug.h>
#include <linux/string.h>
#include <linux/module.h>

/**
* asn1_encode_integer() - encode positive integer 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
* @integer: integer to be encoded
*
* This is a simplified encoder: it only currently does
* positive integers, but it should be simple enough to add the
* negative case if a use comes along.
*/
unsigned char *
asn1_encode_integer(unsigned char *data, const unsigned char *end_data,
      s64 integer)
{
int data_len = end_data - data;
unsigned char *d = &data[2];
bool found = false;
int i;

if (WARN(integer < 0,
   "BUG: integer encode only supports positive integers"))
  return ERR_PTR(-EINVAL);

if (IS_ERR(data))
  return data;

/* need at least 3 bytes for tag, length and integer encoding */
if (data_len < 3)
  return ERR_PTR(-EINVAL);

/* remaining length where at d (the start of the integer encoding) */
data_len -= 2;

data[0] = _tag(UNIV, PRIM, INT);
if (integer == 0) {
  *d++ = 0;
  goto out;
}

for (i = sizeof(integer); i > 0 ; i--) {
  int byte = integer >> (8 * (i - 1));

  if (!found && byte == 0)
   continue;

  /*
* for a positive number the first byte must have bit
* 7 clear in two's complement (otherwise it's a
* negative number) so prepend a leading zero if
* that's not the case
*/
  if (!found && (byte & 0x80)) {
   /*
* no check needed here, we already know we
* have len >= 1
*/
   *d++ = 0;
   data_len--;
  }

  found = true;
  if (data_len == 0)
   return ERR_PTR(-EINVAL);

  *d++ = byte;
  data_len--;
}

out:
data[1] = d - data - 2;

return d;
}
EXPORT_SYMBOL_GPL(asn1_encode_integer);

/* 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)
{
unsigned char *data = *_data;
int start = 7 + 7 + 7 + 7;
int ret = 0;

if (*data_len < 1)
  return -EINVAL;

/* quick case */
if (oid == 0) {
  *data++ = 0x80;
  (*data_len)--;
  goto out;
}

while (oid >> start == 0)
  start -= 7;

while (start > 0 && *data_len > 0) {
  u8 byte;

  byte = oid >> start;
  oid = oid - (byte << start);
  start -= 7;
  byte |= 0x80;
  *data++ = byte;
  (*data_len)--;
}

if (*data_len > 0) {
  *data++ = oid;
  (*data_len)--;
} else {
  ret = -EINVAL;
}

out:
*_data = data;
return ret;
}

/**
* asn1_encode_oid() - encode an oid to ASN.1
* @data: position to begin encoding at
* @end_data: end of data pointer, points one beyond last usable byte in @data
* @oid: array of oids
* @oid_len: length of oid array
*
* this encodes an OID up to ASN.1 when presented as an array of OID values
*/
unsigned char *
asn1_encode_oid(unsigned char *data, const unsigned char *end_data,
  u32 oid[], int oid_len)
{
int data_len = end_data - data;
unsigned char *d = data + 2;
int i, ret;

if (WARN(oid_len < 2, "OID must have at least two elements"))
  return ERR_PTR(-EINVAL);

if (WARN(oid_len > 32, "OID is too large"))
  return ERR_PTR(-EINVAL);

if (IS_ERR(data))
  return data;

/* need at least 3 bytes for tag, length and OID encoding */
if (data_len < 3)
  return ERR_PTR(-EINVAL);

data[0] = _tag(UNIV, PRIM, OID);
*d++ = oid[0] * 40 + oid[1];

data_len -= 3;

for (i = 2; i < oid_len; i++) {
  ret = asn1_encode_oid_digit(&d, &data_len, oid[i]);
  if (ret < 0)
   return ERR_PTR(ret);
}

data[1] = d - data - 2;

return d;
}
EXPORT_SYMBOL_GPL(asn1_encode_oid);

/**
* asn1_encode_length() - encode a length to follow an ASN.1 tag
* @data: pointer to encode at
* @data_len: pointer to remaining length (adjusted by routine)
* @len: length to encode
*
* This routine can encode lengths up to 65535 using the ASN.1 rules.
* It will accept a negative length and place a zero length tag
* instead (to keep the ASN.1 valid).  This convention allows other
* encoder primitives to accept negative lengths as singalling the
* sequence will be re-encoded when the length is known.
*/
static int asn1_encode_length(unsigned char **data, int *data_len, int len)
{
if (*data_len < 1)
  return -EINVAL;

if (len < 0) {
  *((*data)++) = 0;
  (*data_len)--;
  return 0;
}

if (len <= 0x7f) {
  *((*data)++) = len;
  (*data_len)--;
  return 0;
}

if (*data_len < 2)
  return -EINVAL;

if (len <= 0xff) {
  *((*data)++) = 0x81;
  *((*data)++) = len & 0xff;
  *data_len -= 2;
  return 0;
}

if (*data_len < 3)
  return -EINVAL;

if (len <= 0xffff) {
  *((*data)++) = 0x82;
  *((*data)++) = (len >> 8) & 0xff;
  *((*data)++) = len & 0xff;
  *data_len -= 3;
  return 0;
}

if (WARN(len > 0xffffff, "ASN.1 length can't be > 0xffffff"))
  return -EINVAL;

if (*data_len < 4)
  return -EINVAL;
*((*data)++) = 0x83;
*((*data)++) = (len >> 16) & 0xff;
*((*data)++) = (len >> 8) & 0xff;
*((*data)++) = len & 0xff;
*data_len -= 4;

return 0;
}

/**
* asn1_encode_tag() - add a tag for optional or explicit value
* @data: pointer to place tag at
* @end_data: end of data pointer, points one beyond last usable byte in @data
* @tag: tag to be placed
* @string: the data to be tagged
* @len: the length of the data to be tagged
*
* Note this currently only handles short form tags < 31.
*
* Standard usage is to pass in a @tag, @string and @length and the
* @string will be ASN.1 encoded with @tag and placed into @data.  If
* the encoding would put data past @end_data then an error is
* returned, otherwise a pointer to a position one beyond the encoding
* is returned.
*
* To encode in place pass a NULL @string and -1 for @len and the
* maximum allowable beginning and end of the data; all this will do
* is add the current maximum length and update the data pointer to
* the place where the tag contents should be placed is returned.  The
* data should be copied in by the calling routine which should then
* repeat the prior statement but now with the known length.  In order
* to avoid having to keep both before and after pointers, the repeat
* expects to be called with @data pointing to where the first encode
* returned it and still NULL for @string but the real length in @len.
*/
unsigned char *
asn1_encode_tag(unsigned char *data, const unsigned char *end_data,
  u32 tag, const unsigned char *string, int len)
{
int data_len = end_data - data;
int ret;

if (WARN(tag > 30, "ASN.1 tag can't be > 30"))
  return ERR_PTR(-EINVAL);

if (!string && WARN(len > 127,
       "BUG: recode tag is too big (>127)"))
  return ERR_PTR(-EINVAL);

if (IS_ERR(data))
  return data;

if (!string && len > 0) {
  /*
* we're recoding, so move back to the start of the
* tag and install a dummy length because the real
* data_len should be NULL
*/
  data -= 2;
  data_len = 2;
}

if (data_len < 2)
  return ERR_PTR(-EINVAL);

*(data++) = _tagn(CONT, CONS, tag);
data_len--;
ret = asn1_encode_length(&data, &data_len, len);
if (ret < 0)
  return ERR_PTR(ret);

if (!string)
  return data;

if (data_len < len)
  return ERR_PTR(-EINVAL);

memcpy(data, string, len);
data += len;

return data;
}
EXPORT_SYMBOL_GPL(asn1_encode_tag);

/**
* asn1_encode_octet_string() - encode an ASN.1 OCTET STRING
* @data: pointer to encode at
* @end_data: end of data pointer, points one beyond last usable byte in @data
* @string: string to be encoded
* @len: length of string
*
* Note ASN.1 octet strings may contain zeros, so the length is obligatory.
*/
unsigned char *
asn1_encode_octet_string(unsigned char *data,
    const unsigned char *end_data,
    const unsigned char *string, u32 len)
{
int data_len = end_data - data;
int ret;

if (IS_ERR(data))
  return data;

/* need minimum of 2 bytes for tag and length of zero length string */
if (data_len < 2)
  return ERR_PTR(-EINVAL);

*(data++) = _tag(UNIV, PRIM, OTS);
data_len--;

ret = asn1_encode_length(&data, &data_len, len);
if (ret)
  return ERR_PTR(ret);

if (data_len < len)
  return ERR_PTR(-EINVAL);

memcpy(data, string, len);
data += len;

return data;
}
EXPORT_SYMBOL_GPL(asn1_encode_octet_string);

/**
* asn1_encode_sequence() - wrap a byte stream in an ASN.1 SEQUENCE
* @data: pointer to encode at
* @end_data: end of data pointer, points one beyond last usable byte in @data
* @seq: data to be encoded as a sequence
* @len: length of the data to be encoded as a sequence
*
* Fill in a sequence.  To encode in place, pass NULL for @seq and -1
* for @len; then call again once the length is known (still with NULL
* for @seq). In order to avoid having to keep both before and after
* pointers, the repeat expects to be called with @data pointing to
* where the first encode placed it.
*/
unsigned char *
asn1_encode_sequence(unsigned char *data, const unsigned char *end_data,
       const unsigned char *seq, int len)
{
int data_len = end_data - data;
int ret;

if (!seq && WARN(len > 127,
    "BUG: recode sequence is too big (>127)"))
  return ERR_PTR(-EINVAL);

if (IS_ERR(data))
  return data;

if (!seq && len >= 0) {
  /*
* we're recoding, so move back to the start of the
* sequence and install a dummy length because the
* real length should be NULL
*/
  data -= 2;
  data_len = 2;
}

if (data_len < 2)
  return ERR_PTR(-EINVAL);

*(data++) = _tag(UNIV, CONS, SEQ);
data_len--;

ret = asn1_encode_length(&data, &data_len, len);
if (ret)
  return ERR_PTR(ret);

if (!seq)
  return data;

if (data_len < len)
  return ERR_PTR(-EINVAL);

memcpy(data, seq, len);
data += len;

return data;
}
EXPORT_SYMBOL_GPL(asn1_encode_sequence);

/**
* asn1_encode_boolean() - encode a boolean value to ASN.1
* @data: pointer to encode at
* @end_data: end of data pointer, points one beyond last usable byte in @data
* @val: the boolean true/false value
*/
unsigned char *
asn1_encode_boolean(unsigned char *data, const unsigned char *end_data,
      bool val)
{
int data_len = end_data - data;

if (IS_ERR(data))
  return data;

/* booleans are 3 bytes: tag, length == 1 and value == 0 or 1 */
if (data_len < 3)
  return ERR_PTR(-EINVAL);

*(data++) = _tag(UNIV, PRIM, BOOL);
data_len--;

asn1_encode_length(&data, &data_len, 1);

if (val)
  *(data++) = 1;
else
  *(data++) = 0;

return data;
}
EXPORT_SYMBOL_GPL(asn1_encode_boolean);

MODULE_DESCRIPTION("Simple encoder primitives for ASN.1 BER/DER/CER");
MODULE_LICENSE("GPL");

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