// SPDX-License-Identifier: GPL-2.0-or-later
/* Decoder for ASN.1 BER/DER/CER encoded bytestream
 *
 * Copyright (C) 2012 Red Hat, Inc. All Rights Reserved.
 * Written by David Howells (dhowells@redhat.com)
 */

#include <linux/export.h>
#include <linux/kernel.h>
#include <linux/errno.h>
#include <linux/module.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_OR_SKIP]             = 1,
        [ASN1_OP_MATCH_ANY_ACT]                 = 1         + 1,
        [ASN1_OP_MATCH_ANY_ACT_OR_SKIP]         = 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_OR_SKIP]        = 1,
        [ASN1_OP_COND_MATCH_ANY_ACT]            = 1         + 1,
        [ASN1_OP_COND_MATCH_ANY_ACT_OR_SKIP]    = 1         + 1,
        [ASN1_OP_COND_FAIL]                     = 1,
        [ASN1_OP_COMPLETE]                      = 1,
        [ASN1_OP_ACT]                           = 1         + 1,
        [ASN1_OP_MAYBE_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 == ASN1_EOC) {
                /* 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) == ASN1_LONG_TAG)) {
                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)
                goto check_length;

        if (unlikely(len == ASN1_INDEFINITE_LENGTH)) {
                /* 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(len) - 1))
                goto length_too_long;
        if (unlikely(n > datalen - dp))
                goto data_overrun_error;
        len = 0;
        for (; n > 0; n--) {
                len <<= 8;
                len |= data[dp++];
        }
check_length:
        if (len > datalen - dp)
                goto data_overrun_error;
        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;
}

/**
 * asn1_ber_decoder - Decoder BER/DER/CER ASN.1 according to pattern
 * @decoder: The decoder definition (produced by asn1_compiler)
 * @context: The caller's context (to be passed to the action functions)
 * @data: The encoded data
 * @datalen: The size of the encoded data
 *
 * Decode BER/DER/CER encoded ASN.1 data according to a bytecode pattern
 * produced by asn1_compiler.  Action functions are called on marked tags to
 * allow the caller to retrieve significant data.
 *
 * LIMITATIONS:
 *
 * To keep down the amount of stack used by this function, the following limits
 * have been imposed:
 *
 *  (1) This won't handle datalen > 65535 without increasing the size of the
 *      cons stack elements and length_too_long checking.
 *
 *  (2) The stack of constructed types is 10 deep.  If the depth of non-leaf
 *      constructed types exceeds this, the decode will fail.
 *
 *  (3) The SET type (not the SET OF type) isn't really supported as tracking
 *      what members of the set have been seen is a pain.
 */
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_LAST_MATCHED       0x04 /* Last tag matched */
#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) ||
                    (op & ASN1_OP_MATCH__SKIP && dp == datalen)) {
                        flags &= ~FLAG_LAST_MATCHED;
                        pc += asn1_op_lengths[op];
                        goto next_op;
                }

                flags = 0;
                hdr = 2;

                /* Extract a tag from the data */
                if (unlikely(datalen - dp < 2))
                        goto data_overrun_error;
                tag = data[dp++];
                if (unlikely((tag & 0x1f) == ASN1_LONG_TAG))
                        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 == ASN1_INDEFINITE_LENGTH)) {
                                /* 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(n > datalen - dp))
                                        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;
                        }
                } else {
                        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:
        case ASN1_OP_MATCH_OR_SKIP:
        case ASN1_OP_MATCH_ACT:
        case ASN1_OP_MATCH_ACT_OR_SKIP:
        case ASN1_OP_MATCH_ANY:
        case ASN1_OP_MATCH_ANY_OR_SKIP:
        case ASN1_OP_MATCH_ANY_ACT:
        case ASN1_OP_MATCH_ANY_ACT_OR_SKIP:
        case ASN1_OP_COND_MATCH_OR_SKIP:
        case ASN1_OP_COND_MATCH_ACT_OR_SKIP:
        case ASN1_OP_COND_MATCH_ANY:
        case ASN1_OP_COND_MATCH_ANY_OR_SKIP:
        case ASN1_OP_COND_MATCH_ANY_ACT:
        case ASN1_OP_COND_MATCH_ANY_ACT_OR_SKIP:

                if (!(flags & FLAG_CONS)) {
                        if (flags & FLAG_INDEFINITE_LENGTH) {
                                size_t tmp = dp;

                                ret = asn1_find_indefinite_length(
                                        data, datalen, &tmp, &len, &errmsg);
                                if (ret < 0)
                                        goto error;
                        }
                        pr_debug("- LEAF: %zu\n", len);
                }

                if (op & ASN1_OP_MATCH__ACT) {
                        unsigned char act;

                        if (op & ASN1_OP_MATCH__ANY)
                                act = machine[pc + 1];
                        else
                                act = machine[pc + 2];
                        ret = actions[act](context, hdr, tag, data + dp, len);
                        if (ret < 0)
                                return ret;
                }

                if (!(flags & FLAG_CONS))
                        dp += 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;
                fallthrough;

        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);
                        if (ret < 0)
                                return ret;
                }
                pc += asn1_op_lengths[op];
                goto next_op;

        case ASN1_OP_MAYBE_ACT:
                if (!(flags & FLAG_LAST_MATCHED)) {
                        pc += asn1_op_lengths[op];
                        goto next_op;
                }
                fallthrough;

        case ASN1_OP_ACT:
                ret = actions[machine[pc + 1]](context, hdr, tag, data + tdp, len);
                if (ret < 0)
                        return ret;
                pc += asn1_op_lengths[op];
                goto next_op;

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

        default:
                break;
        }

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

MODULE_DESCRIPTION("Decoder for ASN.1 BER/DER/CER encoded bytestream");
MODULE_LICENSE("GPL");