[lwip-devel] [bug #51520] Big endian bug in apps/snmp/snmp_asn1.c

[Art Heers]

Follow-up Comment #5, bug #51520 (project lwip):

A patch with no reference to byte order: tested on a big endian machine.

/**
 * Decodes integer into s32_t.
 *
 * @param pbuf_stream points to a pbuf stream
 * @param len length of the coded integer field
 * @param value return host order integer
 * @return ERR_OK if successful, ERR_ARG if we can't (or won't) decode
 *
 * @note ASN coded integers are _always_ signed!
 */
err_t
snmp_asn1_dec_s32t(struct snmp_pbuf_stream *pbuf_stream, u16_t len, s32_t
*value)
{
  u8_t data;

  if ((len > 0) && (len < 5)) {
    PBUF_OP_EXEC(snmp_pbuf_stream_read(pbuf_stream, &data));

    if (data & 0x80) {
      /* negative, start from -1 */
      *value = (-1 << 8) | data;
    } else {
      /* positive, start from 0 */
      *value = data;
    }
    len--;
    /* shift in the remaining value */
    while (len > 0) {
      PBUF_OP_EXEC(snmp_pbuf_stream_read(pbuf_stream, &data));
      *value = (*value << 8) | data;
      len--;
    }
    return ERR_OK;
  }

  return ERR_VAL;
}


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