asn1.c

snmp up 2

 * asn_parse_length - interprets the length of the current object.
 *  On exit, length contains the value of this length field.
 *
 *  Returns a pointer to the first byte after this length
 *  field (aka: the start of the data field).
 *  Returns NULL on any error.
 
 u_char * asn_parse_length(
 u_char     *data         IN - pointer to start of length field
 u_long     *length       OUT - value of length field
 */
u_char         *
asn_parse_length(u_char * data, u_long * length)
{
    static const char *errpre = "parse length";
    char            ebuf[128];
    register u_char lengthbyte;

    if (!data || !length) {
        ERROR_MSG("parse length: NULL pointer");
        return NULL;
    }
    lengthbyte = *data;

    if (lengthbyte & ASN_LONG_LEN) {
        lengthbyte &= ~ASN_LONG_LEN;    /* turn MSb off */
        if (lengthbyte == 0) {
            snprintf(ebuf, sizeof(ebuf),
                     "%s: indefinite length not supported", errpre);
            ebuf[ sizeof(ebuf)-1 ] = 0;
            ERROR_MSG(ebuf);
            return NULL;
        }
        if (lengthbyte > sizeof(long)) {
            snprintf(ebuf, sizeof(ebuf),
                    "%s: data length %d > %d not supported", errpre,
                    lengthbyte, sizeof(long));
            ebuf[ sizeof(ebuf)-1 ] = 0;
            ERROR_MSG(ebuf);
            return NULL;
        }
        data++;
        *length = 0;            /* protect against short lengths */
        while (lengthbyte--) {
            *length <<= 8;
            *length |= *data++;
        }
        if ((long) *length < 0) {
            snprintf(ebuf, sizeof(ebuf),
                     "%s: negative data length %ld\n", errpre,
                     (long) *length);
            ebuf[ sizeof(ebuf)-1 ] = 0;
            ERROR_MSG(ebuf);
            return NULL;
        }
        return data;
    } else {                    /* short asnlength */
        *length = (long) lengthbyte;
        return data + 1;
    }
}

/*
 * 
 * u_char * asn_build_length(
 * u_char     *data         IN - pointer to start of object
 * int        *datalength   IN/OUT - number of valid bytes left in buffer
 * int         length       IN - length of object
 */
u_char         *
asn_build_length(u_char * data, size_t * datalength, size_t length)
{
    static const char *errpre = "build length";
    char            ebuf[128];

    u_char         *start_data = data;

    /*
     * no indefinite lengths sent 
     */
    if (length < 0x80) {
        if (*datalength < 1) {
            snprintf(ebuf, sizeof(ebuf),
                    "%s: bad length < 1 :%d, %d", errpre,
                    *datalength, length);
            ebuf[ sizeof(ebuf)-1 ] = 0;
            ERROR_MSG(ebuf);
            return NULL;
        }
        *data++ = (u_char) length;
    } else if (length <= 0xFF) {
        if (*datalength < 2) {
            snprintf(ebuf, sizeof(ebuf),
                    "%s: bad length < 2 :%d, %d", errpre,
                    *datalength, length);
            ebuf[ sizeof(ebuf)-1 ] = 0;
            ERROR_MSG(ebuf);
            return NULL;
        }
        *data++ = (u_char) (0x01 | ASN_LONG_LEN);
        *data++ = (u_char) length;
    } else {                    /* 0xFF < length <= 0xFFFF */
        if (*datalength < 3) {
            snprintf(ebuf, sizeof(ebuf),
                    "%s: bad length < 3 :%d, %d", errpre,
                    *datalength, length);
            ebuf[ sizeof(ebuf)-1 ] = 0;
            ERROR_MSG(ebuf);
            return NULL;
        }
        *data++ = (u_char) (0x02 | ASN_LONG_LEN);
        *data++ = (u_char) ((length >> 8) & 0xFF);
        *data++ = (u_char) (length & 0xFF);
    }
    *datalength -= (data - start_data);
    return data;

}

/*
 * asn_parse_objid - pulls an object indentifier out of an ASN object identifier type.
 *  On entry, datalength is input as the number of valid bytes following
 *   "data".  On exit, it is returned as the number of valid bytes
 *   following the beginning of the next object.
 *
 *  "objid" is filled with the object identifier.
 *
 *  Returns a pointer to the first byte past the end
 *   of this object (i.e. the start of the next object).
 *  Returns NULL on any error.
 
 u_char * asn_parse_objid(
 u_char     *data         IN - pointer to start of object
 int        *datalength   IN/OUT - number of valid bytes left in buffer
 u_char     *type         OUT - asn type of object
 oid        *objid        IN/OUT - pointer to start of output buffer
 int        *objidlength  IN/OUT - number of sub-id's in objid
 */
u_char         *
asn_parse_objid(u_char * data,
                size_t * datalength,
                u_char * type, oid * objid, size_t * objidlength)
{
    /*
     * ASN.1 objid ::= 0x06 asnlength subidentifier {subidentifier}*
     * subidentifier ::= {leadingbyte}* lastbyte
     * leadingbyte ::= 1 7bitvalue
     * lastbyte ::= 0 7bitvalue
     */
    register u_char *bufp = data;
    register oid   *oidp = objid + 1;
    register u_long subidentifier;
    register long   length;
    u_long          asn_length;

    *type = *bufp++;
    bufp = asn_parse_length(bufp, &asn_length);
    if (_asn_parse_length_check("parse objid", bufp, data,
                                asn_length, *datalength))
        return NULL;

    *datalength -= (int) asn_length + (bufp - data);

    DEBUGDUMPSETUP("recv", data, bufp - data + asn_length);

    /*
     * Handle invalid object identifier encodings of the form 06 00 robustly 
     */
    if (asn_length == 0)
        objid[0] = objid[1] = 0;

    length = asn_length;
    (*objidlength)--;           /* account for expansion of first byte */

    while (length > 0 && (*objidlength)-- > 0) {
        subidentifier = 0;
        do {                    /* shift and add in low order 7 bits */
            subidentifier =
                (subidentifier << 7) + (*(u_char *) bufp & ~ASN_BIT8);
            length--;
        } while (*(u_char *) bufp++ & ASN_BIT8);        /* last byte has high bit clear */
        /*
         * ?? note, this test will never be true, since the largest value
         * of subidentifier is the value of MAX_SUBID! 
         */
        if (subidentifier > (u_long) MAX_SUBID) {
            ERROR_MSG("subidentifier too large");
            return NULL;
        }
        *oidp++ = (oid) subidentifier;
    }

    /*
     * The first two subidentifiers are encoded into the first component
     * with the value (X * 40) + Y, where:
     *  X is the value of the first subidentifier.
     *  Y is the value of the second subidentifier.
     */
    subidentifier = (u_long) objid[1];
    if (subidentifier == 0x2B) {
        objid[0] = 1;
        objid[1] = 3;
    } else {
        if (subidentifier < 40) {
            objid[0] = 0;
            objid[1] = subidentifier;
        } else if (subidentifier < 80) {
            objid[0] = 1;
            objid[1] = subidentifier - 40;
        } else {
            objid[0] = 2;
            objid[1] = subidentifier - 80;
        }
    }

    *objidlength = (int) (oidp - objid);

    DEBUGMSG(("dumpv_recv", "  ObjID: "));
    DEBUGMSGOID(("dumpv_recv", objid, *objidlength));
    DEBUGMSG(("dumpv_recv", "\n"));
    return bufp;
}

/*
 * asn_build_objid - Builds an ASN object identifier object containing the
 * input string.
 *  On entry, datalength is input as the number of valid bytes following
 *   "data".  On exit, it is returned as the number of valid bytes
 *   following the beginning of the next object.
 *
 *  Returns a pointer to the first byte past the end
 *   of this object (i.e. the start of the next object).
 *  Returns NULL on any error.
 
 u_char * asn_build_objid(
 u_char     *data         IN - pointer to start of object
 int        *datalength   IN/OUT - number of valid bytes left in buffer
 int        type         IN - asn type of object
 oid        *objid        IN - pointer to start of input buffer
 int         objidlength  IN - number of sub-id's in objid
 */
u_char         *
asn_build_objid(u_char * data,
                size_t * datalength,
                u_char type, oid * objid, size_t objidlength)
{
    /*
     * ASN.1 objid ::= 0x06 asnlength subidentifier {subidentifier}*
     * subidentifier ::= {leadingbyte}* lastbyte
     * leadingbyte ::= 1 7bitvalue
     * lastbyte ::= 0 7bitvalue
     */
    size_t          asnlength;
    register oid   *op = objid;
    u_char          objid_size[MAX_OID_LEN];
    register u_long objid_val;
    u_long          first_objid_val;
    register int    i;
#ifndef SNMP_NO_DEBUGGING
    u_char         *initdatap = data;
#endif

    /*
     * check if there are at least 2 sub-identifiers 
     */
    if (objidlength == 0) {
        /*
         * there are not, so make OID have two with value of zero 
         */
        objid_val = 0;
        objidlength = 2;
    } else if (objid[0] > 2) {
        ERROR_MSG("build objid: bad first subidentifier");
        return NULL;
    } else if (objidlength == 1) {
        /*
         * encode the first value 
         */
        objid_val = (op[0] * 40);
        objidlength = 2;
        op++;
    } else {
        /*
         * combine the first two values 
         */
        if ((op[1] > 40) &&
            (op[0] < 2)) {
            ERROR_MSG("build objid: bad second subidentifier");
            return NULL;
        }
        objid_val = (op[0] * 40) + op[1];
        op += 2;
    }
    first_objid_val = objid_val;

    /*
     * ditch illegal calls now 
     */
    if (objidlength > MAX_OID_LEN)
        return NULL;

    /*
     * calculate the number of bytes needed to store the encoded value 
     */
    for (i = 1, asnlength = 0;;) {
        if (objid_val < (unsigned) 0x80) {
            objid_size[i] = 1;
            asnlength += 1;
        } else if (objid_val < (unsigned) 0x4000) {
            objid_size[i] = 2;
            asnlength += 2;
        } else if (objid_val < (unsigned) 0x200000) {
            objid_size[i] = 3;
            asnlength += 3;
        } else if (objid_val < (unsigned) 0x10000000) {
            objid_size[i] = 4;
            asnlength += 4;
        } else {
            objid_size[i] = 5;
            asnlength += 5;
        }
        i++;
        if (i >= (int) objidlength)
            break;
        objid_val = *op++;	/* XXX - doesn't handle 2.X (X > 40) */
    }

    /*
     * store the ASN.1 tag and length 
     */
    data = asn_build_header(data, datalength, type, asnlength);
    if (_asn_build_header_check
        ("build objid", data, *datalength, asnlength))
        return NULL;

    /*
     * store the encoded OID value 
     */
    for (i = 1, objid_val = first_objid_val, op = objid + 2;
         i < (int) objidlength; i++) {
        if (i != 1)
            objid_val = *op++;
        switch (objid_size[i]) {
        case 1:
            *data++ = (u_char) objid_val;
            break;

        case 2:
            *data++ = (u_char) ((objid_val >> 7) | 0x80);
            *data++ = (u_char) (objid_val & 0x07f);
            break;

        case 3:
            *data++ = (u_char) ((objid_val >> 14) | 0x80);
            *data++ = (u_char) ((objid_val >> 7 & 0x7f) | 0x80);
            *data++ = (u_char) (objid_val & 0x07f);
            break;

        case 4:
            *data++ = (u_char) ((objid_val >> 21) | 0x80);
            *data++ = (u_char) ((objid_val >> 14 & 0x7f) | 0x80);
            *data++ = (u_char) ((objid_val >> 7 & 0x7f) | 0x80);
            *data++ = (u_char) (objid_val & 0x07f);
            break;

        case 5:
            *data++ = (u_char) ((objid_val >> 28) | 0x80);
            *data++ = (u_char) ((objid_val >> 21 & 0x7f) | 0x80);
            *data++ = (u_char) ((objid_val >> 14 & 0x7f) | 0x80);
            *data++ = (u_char) ((objid_val >> 7 & 0x7f) | 0x80);
            *data++ = (u_char) (objid_val & 0x07f);
            break;
        }
    }

    /*
     * return the length and data ptr 
     */
    *datalength -= asnlength;
    DEBUGDUMPSETUP("send", initdatap, data - initdatap);
    DEBUGMSG(("dumpv_send", "  ObjID: "));
    DEBUGMSGOID(("dumpv_send", objid, objidlength));
    DEBUGMSG(("dumpv_send", "\n"));
    return data;
}

/*
 * asn_parse_null - Interprets an ASN null type.
 *  On entry, datalength is input as the number of valid bytes following
 *   "data".  On exit, it is returned as the number of valid bytes
 *   following the beginning of the next object.
 *
 *  Returns a pointer to the first byte past the end
 *   of this object (i.e. the start of the next object).
 *  Returns NULL on any error.
 
 u_char * asn_parse_null(
 u_char     *data         IN - pointer to start of object
 int        *datalength   IN/OUT - number of valid bytes left in buffer
 u_char     *type         OUT - asn type of object
 */
u_char         *
asn_parse_null(u_char * data, size_t * datalength, u_char * type)
{
    /*
     * ASN.1 null ::= 0x05 0x00
     */
    register u_char *bufp = data;
    u_long          asn_length;

    *type = *bufp++;
    bufp = asn_parse_length(bufp, &asn_length);
    if (bufp == NULL) {
        ERROR_MSG("parse null: bad length");
        return NULL;
    }
    if (asn_length != 0) {
        ERROR_MSG("parse null: malformed ASN.1 null");
        return NULL;
    }

    *datalength -= (bufp - data);

    DEBUGDUMPSETUP("recv", data, bufp - data);
    DEBUGMSG(("dumpv_recv", "  NULL\n"));

    return bufp + asn_length;