asn1_decoder.c

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/* Decoder for ASN.1 BER/DER/CER encoded bytestream
 *
 * Copyright (C) 2012 Red Hat, Inc. All Rights Reserved.
 * Written by David Howells ([email protected])
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public Licence
 * as published by the Free Software Foundation; either version
 * 2 of the Licence, or (at your option) any later version.
 */

#include <linux/export.h>
#include <linux/kernel.h>
#include <linux/errno.h>
#include <linux/asn1_decoder.h>
#include <linux/asn1_ber_bytecode.h>

static const unsigned char asn1_op_lengths[ASN1_OP__NR] = {
    /*                  OPC TAG JMP ACT */
    [ASN1_OP_MATCH]             = 1 + 1,
    [ASN1_OP_MATCH_OR_SKIP]         = 1 + 1,
    [ASN1_OP_MATCH_ACT]         = 1 + 1     + 1,
    [ASN1_OP_MATCH_ACT_OR_SKIP]     = 1 + 1     + 1,
    [ASN1_OP_MATCH_JUMP]            = 1 + 1 + 1,
    [ASN1_OP_MATCH_JUMP_OR_SKIP]        = 1 + 1 + 1,
    [ASN1_OP_MATCH_ANY]         = 1,
    [ASN1_OP_MATCH_ANY_ACT]         = 1         + 1,
    [ASN1_OP_COND_MATCH_OR_SKIP]        = 1 + 1,
    [ASN1_OP_COND_MATCH_ACT_OR_SKIP]    = 1 + 1     + 1,
    [ASN1_OP_COND_MATCH_JUMP_OR_SKIP]   = 1 + 1 + 1,
    [ASN1_OP_COND_MATCH_ANY]        = 1,
    [ASN1_OP_COND_MATCH_ANY_ACT]        = 1         + 1,
    [ASN1_OP_COND_FAIL]         = 1,
    [ASN1_OP_COMPLETE]          = 1,
    [ASN1_OP_ACT]               = 1         + 1,
    [ASN1_OP_RETURN]            = 1,
    [ASN1_OP_END_SEQ]           = 1,
    [ASN1_OP_END_SEQ_OF]            = 1     + 1,
    [ASN1_OP_END_SET]           = 1,
    [ASN1_OP_END_SET_OF]            = 1     + 1,
    [ASN1_OP_END_SEQ_ACT]           = 1         + 1,
    [ASN1_OP_END_SEQ_OF_ACT]        = 1     + 1 + 1,
    [ASN1_OP_END_SET_ACT]           = 1         + 1,
    [ASN1_OP_END_SET_OF_ACT]        = 1     + 1 + 1,
};

/*
 * Find the length of an indefinite length object
 * @data: The data buffer
 * @datalen: The end of the innermost containing element in the buffer
 * @_dp: The data parse cursor (updated before returning)
 * @_len: Where to return the size of the element.
 * @_errmsg: Where to return a pointer to an error message on error
 */
static int asn1_find_indefinite_length(const unsigned char *data, size_t datalen,
                       size_t *_dp, size_t *_len,
                       const char **_errmsg)
{
    unsigned char tag, tmp;
    size_t dp = *_dp, len, n;
    int indef_level = 1;

next_tag:
    if (unlikely(datalen - dp < 2)) {
        if (datalen == dp)
            goto missing_eoc;
        goto data_overrun_error;
    }

    /* Extract a tag from the data */
    tag = data[dp++];
    if (tag == 0) {
        /* It appears to be an EOC. */
        if (data[dp++] != 0)
            goto invalid_eoc;
        if (--indef_level <= 0) {
            *_len = dp - *_dp;
            *_dp = dp;
            return 0;
        }
        goto next_tag;
    }

    if (unlikely((tag & 0x1f) == 0x1f)) {
        do {
            if (unlikely(datalen - dp < 2))
                goto data_overrun_error;
            tmp = data[dp++];
        } while (tmp & 0x80);
    }

    /* Extract the length */
    len = data[dp++];
    if (len <= 0x7f) {
        dp += len;
        goto next_tag;
    }

    if (unlikely(len == 0x80)) {
        /* Indefinite length */
        if (unlikely((tag & ASN1_CONS_BIT) == ASN1_PRIM << 5))
            goto indefinite_len_primitive;
        indef_level++;
        goto next_tag;
    }

    n = len - 0x80;
    if (unlikely(n > sizeof(size_t) - 1))
        goto length_too_long;
    if (unlikely(n > datalen - dp))
        goto data_overrun_error;
    for (len = 0; n > 0; n--) {
        len <<= 8;
        len |= data[dp++];
    }
    dp += len;
    goto next_tag;

length_too_long:
    *_errmsg = "Unsupported length";
    goto error;
indefinite_len_primitive:
    *_errmsg = "Indefinite len primitive not permitted";
    goto error;
invalid_eoc:
    *_errmsg = "Invalid length EOC";
    goto error;
data_overrun_error:
    *_errmsg = "Data overrun error";
    goto error;
missing_eoc:
    *_errmsg = "Missing EOC in indefinite len cons";
error:
    *_dp = dp;
    return -1;
}

int asn1_ber_decoder(const struct asn1_decoder *decoder,
             void *context,
             const unsigned char *data,
             size_t datalen)
{
    const unsigned char *machine = decoder->machine;
    const asn1_action_t *actions = decoder->actions;
    size_t machlen = decoder->machlen;
    enum asn1_opcode op;
    unsigned char tag = 0, csp = 0, jsp = 0, optag = 0, hdr = 0;
    const char *errmsg;
    size_t pc = 0, dp = 0, tdp = 0, len = 0;
    int ret;

    unsigned char flags = 0;
#define FLAG_INDEFINITE_LENGTH  0x01
#define FLAG_MATCHED        0x02
#define FLAG_CONS       0x20 /* Corresponds to CONS bit in the opcode tag
                      * - ie. whether or not we are going to parse
                      *   a compound type.
                      */

#define NR_CONS_STACK 10
    unsigned short cons_dp_stack[NR_CONS_STACK];
    unsigned short cons_datalen_stack[NR_CONS_STACK];
    unsigned char cons_hdrlen_stack[NR_CONS_STACK];
#define NR_JUMP_STACK 10
    unsigned char jump_stack[NR_JUMP_STACK];

    if (datalen > 65535)
        return -EMSGSIZE;

next_op:
    pr_debug("next_op: pc=\e[32m%zu\e[m/%zu dp=\e[33m%zu\e[m/%zu C=%d J=%d\n",
         pc, machlen, dp, datalen, csp, jsp);
    if (unlikely(pc >= machlen))
        goto machine_overrun_error;
    op = machine[pc];
    if (unlikely(pc + asn1_op_lengths[op] > machlen))
        goto machine_overrun_error;

    /* If this command is meant to match a tag, then do that before
     * evaluating the command.
     */
    if (op <= ASN1_OP__MATCHES_TAG) {
        unsigned char tmp;

        /* Skip conditional matches if possible */
        if ((op & ASN1_OP_MATCH__COND &&
             flags & FLAG_MATCHED) ||
            dp == datalen) {
            pc += asn1_op_lengths[op];
            goto next_op;
        }

        flags = 0;
        hdr = 2;

        /* Extract a tag from the data */
        if (unlikely(dp >= datalen - 1))
            goto data_overrun_error;
        tag = data[dp++];
        if (unlikely((tag & 0x1f) == 0x1f))
            goto long_tag_not_supported;

        if (op & ASN1_OP_MATCH__ANY) {
            pr_debug("- any %02x\n", tag);
        } else {
            /* Extract the tag from the machine
             * - Either CONS or PRIM are permitted in the data if
             *   CONS is not set in the op stream, otherwise CONS
             *   is mandatory.
             */
            optag = machine[pc + 1];
            flags |= optag & FLAG_CONS;

            /* Determine whether the tag matched */
            tmp = optag ^ tag;
            tmp &= ~(optag & ASN1_CONS_BIT);
            pr_debug("- match? %02x %02x %02x\n", tag, optag, tmp);
            if (tmp != 0) {
                /* All odd-numbered tags are MATCH_OR_SKIP. */
                if (op & ASN1_OP_MATCH__SKIP) {
                    pc += asn1_op_lengths[op];
                    dp--;
                    goto next_op;
                }
                goto tag_mismatch;
            }
        }
        flags |= FLAG_MATCHED;

        len = data[dp++];
        if (len > 0x7f) {
            if (unlikely(len == 0x80)) {
                /* Indefinite length */
                if (unlikely(!(tag & ASN1_CONS_BIT)))
                    goto indefinite_len_primitive;
                flags |= FLAG_INDEFINITE_LENGTH;
                if (unlikely(2 > datalen - dp))
                    goto data_overrun_error;
            } else {
                int n = len - 0x80;
                if (unlikely(n > 2))
                    goto length_too_long;
                if (unlikely(dp >= datalen - n))
                    goto data_overrun_error;
                hdr += n;
                for (len = 0; n > 0; n--) {
                    len <<= 8;
                    len |= data[dp++];
                }
                if (unlikely(len > datalen - dp))
                    goto data_overrun_error;
            }
        }

        if (flags & FLAG_CONS) {
            /* For expected compound forms, we stack the positions
             * of the start and end of the data.
             */
            if (unlikely(csp >= NR_CONS_STACK))
                goto cons_stack_overflow;
            cons_dp_stack[csp] = dp;
            cons_hdrlen_stack[csp] = hdr;
            if (!(flags & FLAG_INDEFINITE_LENGTH)) {
                cons_datalen_stack[csp] = datalen;
                datalen = dp + len;
            } else {
                cons_datalen_stack[csp] = 0;
            }
            csp++;
        }

        pr_debug("- TAG: %02x %zu%s\n",
             tag, len, flags & FLAG_CONS ? " CONS" : "");
        tdp = dp;
    }

    /* Decide how to handle the operation */
    switch (op) {
    case ASN1_OP_MATCH_ANY_ACT:
    case ASN1_OP_COND_MATCH_ANY_ACT:
        ret = actions[machine[pc + 1]](context, hdr, tag, data + dp, len);
        if (ret < 0)
            return ret;
        goto skip_data;

    case ASN1_OP_MATCH_ACT:
    case ASN1_OP_MATCH_ACT_OR_SKIP:
    case ASN1_OP_COND_MATCH_ACT_OR_SKIP:
        ret = actions[machine[pc + 2]](context, hdr, tag, data + dp, len);
        if (ret < 0)
            return ret;
        goto skip_data;

    case ASN1_OP_MATCH:
    case ASN1_OP_MATCH_OR_SKIP:
    case ASN1_OP_MATCH_ANY:
    case ASN1_OP_COND_MATCH_OR_SKIP:
    case ASN1_OP_COND_MATCH_ANY:
    skip_data:
        if (!(flags & FLAG_CONS)) {
            if (flags & FLAG_INDEFINITE_LENGTH) {
                ret = asn1_find_indefinite_length(
                    data, datalen, &dp, &len, &errmsg);
                if (ret < 0)
                    goto error;
            } else {
                dp += len;
            }
            pr_debug("- LEAF: %zu\n", len);
        }
        pc += asn1_op_lengths[op];
        goto next_op;

    case ASN1_OP_MATCH_JUMP:
    case ASN1_OP_MATCH_JUMP_OR_SKIP:
    case ASN1_OP_COND_MATCH_JUMP_OR_SKIP:
        pr_debug("- MATCH_JUMP\n");
        if (unlikely(jsp == NR_JUMP_STACK))
            goto jump_stack_overflow;
        jump_stack[jsp++] = pc + asn1_op_lengths[op];
        pc = machine[pc + 2];
        goto next_op;

    case ASN1_OP_COND_FAIL:
        if (unlikely(!(flags & FLAG_MATCHED)))
            goto tag_mismatch;
        pc += asn1_op_lengths[op];
        goto next_op;

    case ASN1_OP_COMPLETE:
        if (unlikely(jsp != 0 || csp != 0)) {
            pr_err("ASN.1 decoder error: Stacks not empty at completion (%u, %u)\n",
                   jsp, csp);
            return -EBADMSG;
        }
        return 0;

    case ASN1_OP_END_SET:
    case ASN1_OP_END_SET_ACT:
        if (unlikely(!(flags & FLAG_MATCHED)))
            goto tag_mismatch;
    case ASN1_OP_END_SEQ:
    case ASN1_OP_END_SET_OF:
    case ASN1_OP_END_SEQ_OF:
    case ASN1_OP_END_SEQ_ACT:
    case ASN1_OP_END_SET_OF_ACT:
    case ASN1_OP_END_SEQ_OF_ACT:
        if (unlikely(csp <= 0))
            goto cons_stack_underflow;
        csp--;
        tdp = cons_dp_stack[csp];
        hdr = cons_hdrlen_stack[csp];
        len = datalen;
        datalen = cons_datalen_stack[csp];
        pr_debug("- end cons t=%zu dp=%zu l=%zu/%zu\n",
             tdp, dp, len, datalen);
        if (datalen == 0) {
            /* Indefinite length - check for the EOC. */
            datalen = len;
            if (unlikely(datalen - dp < 2))
                goto data_overrun_error;
            if (data[dp++] != 0) {
                if (op & ASN1_OP_END__OF) {
                    dp--;
                    csp++;
                    pc = machine[pc + 1];
                    pr_debug("- continue\n");
                    goto next_op;
                }
                goto missing_eoc;
            }
            if (data[dp++] != 0)
                goto invalid_eoc;
            len = dp - tdp - 2;
        } else {
            if (dp < len && (op & ASN1_OP_END__OF)) {
                datalen = len;
                csp++;
                pc = machine[pc + 1];
                pr_debug("- continue\n");
                goto next_op;
            }
            if (dp != len)
                goto cons_length_error;
            len -= tdp;
            pr_debug("- cons len l=%zu d=%zu\n", len, dp - tdp);
        }

        if (op & ASN1_OP_END__ACT) {
            unsigned char act;
            if (op & ASN1_OP_END__OF)
                act = machine[pc + 2];
            else
                act = machine[pc + 1];
            ret = actions[act](context, hdr, 0, data + tdp, len);
        }
        pc += asn1_op_lengths[op];
        goto next_op;

    case ASN1_OP_ACT:
        ret = actions[machine[pc + 1]](context, hdr, tag, data + tdp, len);
        pc += asn1_op_lengths[op];
        goto next_op;

    case ASN1_OP_RETURN:
        if (unlikely(jsp <= 0))
            goto jump_stack_underflow;
        pc = jump_stack[--jsp];
        goto next_op;

    default:
        break;
    }

    /* Shouldn't reach here */
    pr_err("ASN.1 decoder error: Found reserved opcode (%u)\n", op);
    return -EBADMSG;

data_overrun_error:
    errmsg = "Data overrun error";
    goto error;
machine_overrun_error:
    errmsg = "Machine overrun error";
    goto error;
jump_stack_underflow:
    errmsg = "Jump stack underflow";
    goto error;
jump_stack_overflow:
    errmsg = "Jump stack overflow";
    goto error;
cons_stack_underflow:
    errmsg = "Cons stack underflow";
    goto error;
cons_stack_overflow:
    errmsg = "Cons stack overflow";
    goto error;
cons_length_error:
    errmsg = "Cons length error";
    goto error;
missing_eoc:
    errmsg = "Missing EOC in indefinite len cons";
    goto error;
invalid_eoc:
    errmsg = "Invalid length EOC";
    goto error;
length_too_long:
    errmsg = "Unsupported length";
    goto error;
indefinite_len_primitive:
    errmsg = "Indefinite len primitive not permitted";
    goto error;
tag_mismatch:
    errmsg = "Unexpected tag";
    goto error;
long_tag_not_supported:
    errmsg = "Long tag not supported";
error:
    pr_debug("\nASN1: %s [m=%zu d=%zu ot=%02x t=%02x l=%zu]\n",
         errmsg, pc, dp, optag, tag, len);
    return -EBADMSG;
}
EXPORT_SYMBOL_GPL(asn1_ber_decoder);