ber_tlv_length.c

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/*-
 * Copyright (c) 2003, 2004 Lev Walkin <vlm@lionet.info>. All rights reserved.
 * Redistribution and modifications are permitted subject to BSD license.
 */
#include <asn_internal.h>
#include <ber_tlv_length.h>
#include <ber_tlv_tag.h>

ssize_t
ber_fetch_length(int _is_constructed, const void *bufptr, size_t size,
        ber_tlv_len_t *len_r) {
    const uint8_t *buf = (const uint8_t *)bufptr;
    unsigned oct;

    if(size == 0)
        return 0;   /* Want more */

    oct = *(const uint8_t *)buf;
    if((oct & 0x80) == 0) {
        /*
         * Short definite length.
         */
        *len_r = oct;   /* & 0x7F */
        return 1;
    } else {
        ber_tlv_len_t len;
        size_t skipped;

        if(_is_constructed && oct == 0x80) {
            *len_r = -1;    /* Indefinite length */
            return 1;
        }

        if(oct == 0xff) {
            /* Reserved in standard for future use. */
            return -1;
        }

        oct &= 0x7F;    /* Leave only the 7 LS bits */
        for(len = 0, buf++, skipped = 1;
            oct && (++skipped <= size); buf++, oct--) {

            len = (len << 8) | *buf;
            if(len < 0
            || (len >> ((8 * sizeof(len)) - 8) && oct > 1)) {
                /*
                 * Too large length value.
                 */
                return -1;
            }
        }

        if(oct == 0) {
            ber_tlv_len_t lenplusepsilon = (size_t)len + 1024;
            /*
             * Here length may be very close or equal to 2G.
             * However, the arithmetics used in some decoders
             * may add some (small) quantities to the length,
             * to check the resulting value against some limits.
             * This may result in integer wrap-around, which
             * we try to avoid by checking it earlier here.
             */
            if(lenplusepsilon < 0) {
                /* Too large length value */
                return -1;
            }

            *len_r = len;
            return skipped;
        }

        return 0;   /* Want more */
    }

}

ssize_t
ber_skip_length(asn_codec_ctx_t *opt_codec_ctx,
        int _is_constructed, const void *ptr, size_t size) {
    ber_tlv_len_t vlen; /* Length of V in TLV */
    ssize_t tl;     /* Length of L in TLV */
    ssize_t ll;     /* Length of L in TLV */
    size_t skip;

    /*
     * Make sure we didn't exceed the maximum stack size.
     */
    if(_ASN_STACK_OVERFLOW_CHECK(opt_codec_ctx))
        return -1;

    /*
     * Determine the size of L in TLV.
     */
    ll = ber_fetch_length(_is_constructed, ptr, size, &vlen);
    if(ll <= 0) return ll;

    /*
     * Definite length.
     */
    if(vlen >= 0) {
        skip = ll + vlen;
        if(skip > size)
            return 0;   /* Want more */
        return skip;
    }

    /*
     * Indefinite length!
     */
    ASN_DEBUG("Skipping indefinite length");
    for(skip = ll, ptr = ((const char *)ptr) + ll, size -= ll;;) {
        ber_tlv_tag_t tag;

        /* Fetch the tag */
        tl = ber_fetch_tag(ptr, size, &tag);
        if(tl <= 0) return tl;

        ll = ber_skip_length(opt_codec_ctx,
            BER_TLV_CONSTRUCTED(ptr),
            ((const char *)ptr) + tl, size - tl);
        if(ll <= 0) return ll;

        skip += tl + ll;

        /*
         * This may be the end of the indefinite length structure,
         * two consecutive 0 octets.
         * Check if it is true.
         */
        if(((const uint8_t *)ptr)[0] == 0
        && ((const uint8_t *)ptr)[1] == 0)
            return skip;

        ptr = ((const char *)ptr) + tl + ll;
        size -= tl + ll;
    }

    /* UNREACHABLE */
}

size_t
der_tlv_length_serialize(ber_tlv_len_t len, void *bufp, size_t size) {
    size_t required_size;   /* Size of len encoding */
    uint8_t *buf = (uint8_t *)bufp;
    uint8_t *end;
    size_t i;

    if(len <= 127) {
        /* Encoded in 1 octet */
        if(size) *buf = (uint8_t)len;
        return 1;
    }

    /*
     * Compute the size of the subsequent bytes.
     */
    for(required_size = 1, i = 8; i < 8 * sizeof(len); i += 8) {
        if(len >> i)
            required_size++;
        else
            break;
    }

    if(size <= required_size)
        return required_size + 1;

    *buf++ = (uint8_t)(0x80 | required_size);  /* Length of the encoding */

    /*
     * Produce the len encoding, space permitting.
     */
    end = buf + required_size;
    for(i -= 8; buf < end; i -= 8, buf++)
        *buf = (uint8_t)(len >> i);

    return required_size + 1;
}