xz_dec_stream.c

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/*
 * .xz Stream decoder
 *
 * Author: Lasse Collin <[email protected]>
 *
 * This file has been put into the public domain.
 * You can do whatever you want with this file.
 */

#include "xz_private.h"
#include "xz_stream.h"

/* Hash used to validate the Index field */
struct xz_dec_hash {
    vli_type unpadded;
    vli_type uncompressed;
    uint32_t crc32;
};

struct xz_dec {
    /* Position in dec_main() */
    enum {
        SEQ_STREAM_HEADER,
        SEQ_BLOCK_START,
        SEQ_BLOCK_HEADER,
        SEQ_BLOCK_UNCOMPRESS,
        SEQ_BLOCK_PADDING,
        SEQ_BLOCK_CHECK,
        SEQ_INDEX,
        SEQ_INDEX_PADDING,
        SEQ_INDEX_CRC32,
        SEQ_STREAM_FOOTER
    } sequence;

    /* Position in variable-length integers and Check fields */
    uint32_t pos;

    /* Variable-length integer decoded by dec_vli() */
    vli_type vli;

    /* Saved in_pos and out_pos */
    size_t in_start;
    size_t out_start;

    /* CRC32 value in Block or Index */
    uint32_t crc32;

    /* Type of the integrity check calculated from uncompressed data */
    enum xz_check check_type;

    /* Operation mode */
    enum xz_mode mode;

    /*
     * True if the next call to xz_dec_run() is allowed to return
     * XZ_BUF_ERROR.
     */
    bool allow_buf_error;

    /* Information stored in Block Header */
    struct {
        /*
         * Value stored in the Compressed Size field, or
         * VLI_UNKNOWN if Compressed Size is not present.
         */
        vli_type compressed;

        /*
         * Value stored in the Uncompressed Size field, or
         * VLI_UNKNOWN if Uncompressed Size is not present.
         */
        vli_type uncompressed;

        /* Size of the Block Header field */
        uint32_t size;
    } block_header;

    /* Information collected when decoding Blocks */
    struct {
        /* Observed compressed size of the current Block */
        vli_type compressed;

        /* Observed uncompressed size of the current Block */
        vli_type uncompressed;

        /* Number of Blocks decoded so far */
        vli_type count;

        /*
         * Hash calculated from the Block sizes. This is used to
         * validate the Index field.
         */
        struct xz_dec_hash hash;
    } block;

    /* Variables needed when verifying the Index field */
    struct {
        /* Position in dec_index() */
        enum {
            SEQ_INDEX_COUNT,
            SEQ_INDEX_UNPADDED,
            SEQ_INDEX_UNCOMPRESSED
        } sequence;

        /* Size of the Index in bytes */
        vli_type size;

        /* Number of Records (matches block.count in valid files) */
        vli_type count;

        /*
         * Hash calculated from the Records (matches block.hash in
         * valid files).
         */
        struct xz_dec_hash hash;
    } index;

    /*
     * Temporary buffer needed to hold Stream Header, Block Header,
     * and Stream Footer. The Block Header is the biggest (1 KiB)
     * so we reserve space according to that. buf[] has to be aligned
     * to a multiple of four bytes; the size_t variables before it
     * should guarantee this.
     */
    struct {
        size_t pos;
        size_t size;
        uint8_t buf[1024];
    } temp;

    struct xz_dec_lzma2 *lzma2;

#ifdef XZ_DEC_BCJ
    struct xz_dec_bcj *bcj;
    bool bcj_active;
#endif
};

#ifdef XZ_DEC_ANY_CHECK
/* Sizes of the Check field with different Check IDs */
static const uint8_t check_sizes[16] = {
    0,
    4, 4, 4,
    8, 8, 8,
    16, 16, 16,
    32, 32, 32,
    64, 64, 64
};
#endif

/*
 * Fill s->temp by copying data starting from b->in[b->in_pos]. Caller
 * must have set s->temp.pos to indicate how much data we are supposed
 * to copy into s->temp.buf. Return true once s->temp.pos has reached
 * s->temp.size.
 */
static bool fill_temp(struct xz_dec *s, struct xz_buf *b)
{
    size_t copy_size = min_t(size_t,
            b->in_size - b->in_pos, s->temp.size - s->temp.pos);

    memcpy(s->temp.buf + s->temp.pos, b->in + b->in_pos, copy_size);
    b->in_pos += copy_size;
    s->temp.pos += copy_size;

    if (s->temp.pos == s->temp.size) {
        s->temp.pos = 0;
        return true;
    }

    return false;
}

/* Decode a variable-length integer (little-endian base-128 encoding) */
static enum xz_ret dec_vli(struct xz_dec *s, const uint8_t *in,
               size_t *in_pos, size_t in_size)
{
    uint8_t byte;

    if (s->pos == 0)
        s->vli = 0;

    while (*in_pos < in_size) {
        byte = in[*in_pos];
        ++*in_pos;

        s->vli |= (vli_type)(byte & 0x7F) << s->pos;

        if ((byte & 0x80) == 0) {
            /* Don't allow non-minimal encodings. */
            if (byte == 0 && s->pos != 0)
                return XZ_DATA_ERROR;

            s->pos = 0;
            return XZ_STREAM_END;
        }

        s->pos += 7;
        if (s->pos == 7 * VLI_BYTES_MAX)
            return XZ_DATA_ERROR;
    }

    return XZ_OK;
}

/*
 * Decode the Compressed Data field from a Block. Update and validate
 * the observed compressed and uncompressed sizes of the Block so that
 * they don't exceed the values possibly stored in the Block Header
 * (validation assumes that no integer overflow occurs, since vli_type
 * is normally uint64_t). Update the CRC32 if presence of the CRC32
 * field was indicated in Stream Header.
 *
 * Once the decoding is finished, validate that the observed sizes match
 * the sizes possibly stored in the Block Header. Update the hash and
 * Block count, which are later used to validate the Index field.
 */
static enum xz_ret dec_block(struct xz_dec *s, struct xz_buf *b)
{
    enum xz_ret ret;

    s->in_start = b->in_pos;
    s->out_start = b->out_pos;

#ifdef XZ_DEC_BCJ
    if (s->bcj_active)
        ret = xz_dec_bcj_run(s->bcj, s->lzma2, b);
    else
#endif
        ret = xz_dec_lzma2_run(s->lzma2, b);

    s->block.compressed += b->in_pos - s->in_start;
    s->block.uncompressed += b->out_pos - s->out_start;

    /*
     * There is no need to separately check for VLI_UNKNOWN, since
     * the observed sizes are always smaller than VLI_UNKNOWN.
     */
    if (s->block.compressed > s->block_header.compressed
            || s->block.uncompressed
                > s->block_header.uncompressed)
        return XZ_DATA_ERROR;

    if (s->check_type == XZ_CHECK_CRC32)
        s->crc32 = xz_crc32(b->out + s->out_start,
                b->out_pos - s->out_start, s->crc32);

    if (ret == XZ_STREAM_END) {
        if (s->block_header.compressed != VLI_UNKNOWN
                && s->block_header.compressed
                    != s->block.compressed)
            return XZ_DATA_ERROR;

        if (s->block_header.uncompressed != VLI_UNKNOWN
                && s->block_header.uncompressed
                    != s->block.uncompressed)
            return XZ_DATA_ERROR;

        s->block.hash.unpadded += s->block_header.size
                + s->block.compressed;

#ifdef XZ_DEC_ANY_CHECK
        s->block.hash.unpadded += check_sizes[s->check_type];
#else
        if (s->check_type == XZ_CHECK_CRC32)
            s->block.hash.unpadded += 4;
#endif

        s->block.hash.uncompressed += s->block.uncompressed;
        s->block.hash.crc32 = xz_crc32(
                (const uint8_t *)&s->block.hash,
                sizeof(s->block.hash), s->block.hash.crc32);

        ++s->block.count;
    }

    return ret;
}

/* Update the Index size and the CRC32 value. */
static void index_update(struct xz_dec *s, const struct xz_buf *b)
{
    size_t in_used = b->in_pos - s->in_start;
    s->index.size += in_used;
    s->crc32 = xz_crc32(b->in + s->in_start, in_used, s->crc32);
}

/*
 * Decode the Number of Records, Unpadded Size, and Uncompressed Size
 * fields from the Index field. That is, Index Padding and CRC32 are not
 * decoded by this function.
 *
 * This can return XZ_OK (more input needed), XZ_STREAM_END (everything
 * successfully decoded), or XZ_DATA_ERROR (input is corrupt).
 */
static enum xz_ret dec_index(struct xz_dec *s, struct xz_buf *b)
{
    enum xz_ret ret;

    do {
        ret = dec_vli(s, b->in, &b->in_pos, b->in_size);
        if (ret != XZ_STREAM_END) {
            index_update(s, b);
            return ret;
        }

        switch (s->index.sequence) {
        case SEQ_INDEX_COUNT:
            s->index.count = s->vli;

            /*
             * Validate that the Number of Records field
             * indicates the same number of Records as
             * there were Blocks in the Stream.
             */
            if (s->index.count != s->block.count)
                return XZ_DATA_ERROR;

            s->index.sequence = SEQ_INDEX_UNPADDED;
            break;

        case SEQ_INDEX_UNPADDED:
            s->index.hash.unpadded += s->vli;
            s->index.sequence = SEQ_INDEX_UNCOMPRESSED;
            break;

        case SEQ_INDEX_UNCOMPRESSED:
            s->index.hash.uncompressed += s->vli;
            s->index.hash.crc32 = xz_crc32(
                    (const uint8_t *)&s->index.hash,
                    sizeof(s->index.hash),
                    s->index.hash.crc32);
            --s->index.count;
            s->index.sequence = SEQ_INDEX_UNPADDED;
            break;
        }
    } while (s->index.count > 0);

    return XZ_STREAM_END;
}

/*
 * Validate that the next four input bytes match the value of s->crc32.
 * s->pos must be zero when starting to validate the first byte.
 */
static enum xz_ret crc32_validate(struct xz_dec *s, struct xz_buf *b)
{
    do {
        if (b->in_pos == b->in_size)
            return XZ_OK;

        if (((s->crc32 >> s->pos) & 0xFF) != b->in[b->in_pos++])
            return XZ_DATA_ERROR;

        s->pos += 8;

    } while (s->pos < 32);

    s->crc32 = 0;
    s->pos = 0;

    return XZ_STREAM_END;
}

#ifdef XZ_DEC_ANY_CHECK
/*
 * Skip over the Check field when the Check ID is not supported.
 * Returns true once the whole Check field has been skipped over.
 */
static bool check_skip(struct xz_dec *s, struct xz_buf *b)
{
    while (s->pos < check_sizes[s->check_type]) {
        if (b->in_pos == b->in_size)
            return false;

        ++b->in_pos;
        ++s->pos;
    }

    s->pos = 0;

    return true;
}
#endif

/* Decode the Stream Header field (the first 12 bytes of the .xz Stream). */
static enum xz_ret dec_stream_header(struct xz_dec *s)
{
    if (!memeq(s->temp.buf, HEADER_MAGIC, HEADER_MAGIC_SIZE))
        return XZ_FORMAT_ERROR;

    if (xz_crc32(s->temp.buf + HEADER_MAGIC_SIZE, 2, 0)
            != get_le32(s->temp.buf + HEADER_MAGIC_SIZE + 2))
        return XZ_DATA_ERROR;

    if (s->temp.buf[HEADER_MAGIC_SIZE] != 0)
        return XZ_OPTIONS_ERROR;

    /*
     * Of integrity checks, we support only none (Check ID = 0) and
     * CRC32 (Check ID = 1). However, if XZ_DEC_ANY_CHECK is defined,
     * we will accept other check types too, but then the check won't
     * be verified and a warning (XZ_UNSUPPORTED_CHECK) will be given.
     */
    s->check_type = s->temp.buf[HEADER_MAGIC_SIZE + 1];

#ifdef XZ_DEC_ANY_CHECK
    if (s->check_type > XZ_CHECK_MAX)
        return XZ_OPTIONS_ERROR;

    if (s->check_type > XZ_CHECK_CRC32)
        return XZ_UNSUPPORTED_CHECK;
#else
    if (s->check_type > XZ_CHECK_CRC32)
        return XZ_OPTIONS_ERROR;
#endif

    return XZ_OK;
}

/* Decode the Stream Footer field (the last 12 bytes of the .xz Stream) */
static enum xz_ret dec_stream_footer(struct xz_dec *s)
{
    if (!memeq(s->temp.buf + 10, FOOTER_MAGIC, FOOTER_MAGIC_SIZE))
        return XZ_DATA_ERROR;

    if (xz_crc32(s->temp.buf + 4, 6, 0) != get_le32(s->temp.buf))
        return XZ_DATA_ERROR;

    /*
     * Validate Backward Size. Note that we never added the size of the
     * Index CRC32 field to s->index.size, thus we use s->index.size / 4
     * instead of s->index.size / 4 - 1.
     */
    if ((s->index.size >> 2) != get_le32(s->temp.buf + 4))
        return XZ_DATA_ERROR;

    if (s->temp.buf[8] != 0 || s->temp.buf[9] != s->check_type)
        return XZ_DATA_ERROR;

    /*
     * Use XZ_STREAM_END instead of XZ_OK to be more convenient
     * for the caller.
     */
    return XZ_STREAM_END;
}

/* Decode the Block Header and initialize the filter chain. */
static enum xz_ret dec_block_header(struct xz_dec *s)
{
    enum xz_ret ret;

    /*
     * Validate the CRC32. We know that the temp buffer is at least
     * eight bytes so this is safe.
     */
    s->temp.size -= 4;
    if (xz_crc32(s->temp.buf, s->temp.size, 0)
            != get_le32(s->temp.buf + s->temp.size))
        return XZ_DATA_ERROR;

    s->temp.pos = 2;

    /*
     * Catch unsupported Block Flags. We support only one or two filters
     * in the chain, so we catch that with the same test.
     */
#ifdef XZ_DEC_BCJ
    if (s->temp.buf[1] & 0x3E)
#else
    if (s->temp.buf[1] & 0x3F)
#endif
        return XZ_OPTIONS_ERROR;

    /* Compressed Size */
    if (s->temp.buf[1] & 0x40) {
        if (dec_vli(s, s->temp.buf, &s->temp.pos, s->temp.size)
                    != XZ_STREAM_END)
            return XZ_DATA_ERROR;

        s->block_header.compressed = s->vli;
    } else {
        s->block_header.compressed = VLI_UNKNOWN;
    }

    /* Uncompressed Size */
    if (s->temp.buf[1] & 0x80) {
        if (dec_vli(s, s->temp.buf, &s->temp.pos, s->temp.size)
                != XZ_STREAM_END)
            return XZ_DATA_ERROR;

        s->block_header.uncompressed = s->vli;
    } else {
        s->block_header.uncompressed = VLI_UNKNOWN;
    }

#ifdef XZ_DEC_BCJ
    /* If there are two filters, the first one must be a BCJ filter. */
    s->bcj_active = s->temp.buf[1] & 0x01;
    if (s->bcj_active) {
        if (s->temp.size - s->temp.pos < 2)
            return XZ_OPTIONS_ERROR;

        ret = xz_dec_bcj_reset(s->bcj, s->temp.buf[s->temp.pos++]);
        if (ret != XZ_OK)
            return ret;

        /*
         * We don't support custom start offset,
         * so Size of Properties must be zero.
         */
        if (s->temp.buf[s->temp.pos++] != 0x00)
            return XZ_OPTIONS_ERROR;
    }
#endif

    /* Valid Filter Flags always take at least two bytes. */
    if (s->temp.size - s->temp.pos < 2)
        return XZ_DATA_ERROR;

    /* Filter ID = LZMA2 */
    if (s->temp.buf[s->temp.pos++] != 0x21)
        return XZ_OPTIONS_ERROR;

    /* Size of Properties = 1-byte Filter Properties */
    if (s->temp.buf[s->temp.pos++] != 0x01)
        return XZ_OPTIONS_ERROR;

    /* Filter Properties contains LZMA2 dictionary size. */
    if (s->temp.size - s->temp.pos < 1)
        return XZ_DATA_ERROR;

    ret = xz_dec_lzma2_reset(s->lzma2, s->temp.buf[s->temp.pos++]);
    if (ret != XZ_OK)
        return ret;

    /* The rest must be Header Padding. */
    while (s->temp.pos < s->temp.size)
        if (s->temp.buf[s->temp.pos++] != 0x00)
            return XZ_OPTIONS_ERROR;

    s->temp.pos = 0;
    s->block.compressed = 0;
    s->block.uncompressed = 0;

    return XZ_OK;
}

static enum xz_ret dec_main(struct xz_dec *s, struct xz_buf *b)
{
    enum xz_ret ret;

    /*
     * Store the start position for the case when we are in the middle
     * of the Index field.
     */
    s->in_start = b->in_pos;

    while (true) {
        switch (s->sequence) {
        case SEQ_STREAM_HEADER:
            /*
             * Stream Header is copied to s->temp, and then
             * decoded from there. This way if the caller
             * gives us only little input at a time, we can
             * still keep the Stream Header decoding code
             * simple. Similar approach is used in many places
             * in this file.
             */
            if (!fill_temp(s, b))
                return XZ_OK;

            /*
             * If dec_stream_header() returns
             * XZ_UNSUPPORTED_CHECK, it is still possible
             * to continue decoding if working in multi-call
             * mode. Thus, update s->sequence before calling
             * dec_stream_header().
             */
            s->sequence = SEQ_BLOCK_START;

            ret = dec_stream_header(s);
            if (ret != XZ_OK)
                return ret;

        case SEQ_BLOCK_START:
            /* We need one byte of input to continue. */
            if (b->in_pos == b->in_size)
                return XZ_OK;

            /* See if this is the beginning of the Index field. */
            if (b->in[b->in_pos] == 0) {
                s->in_start = b->in_pos++;
                s->sequence = SEQ_INDEX;
                break;
            }

            /*
             * Calculate the size of the Block Header and
             * prepare to decode it.
             */
            s->block_header.size
                = ((uint32_t)b->in[b->in_pos] + 1) * 4;

            s->temp.size = s->block_header.size;
            s->temp.pos = 0;
            s->sequence = SEQ_BLOCK_HEADER;

        case SEQ_BLOCK_HEADER:
            if (!fill_temp(s, b))
                return XZ_OK;

            ret = dec_block_header(s);
            if (ret != XZ_OK)
                return ret;

            s->sequence = SEQ_BLOCK_UNCOMPRESS;

        case SEQ_BLOCK_UNCOMPRESS:
            ret = dec_block(s, b);
            if (ret != XZ_STREAM_END)
                return ret;

            s->sequence = SEQ_BLOCK_PADDING;

        case SEQ_BLOCK_PADDING:
            /*
             * Size of Compressed Data + Block Padding
             * must be a multiple of four. We don't need
             * s->block.compressed for anything else
             * anymore, so we use it here to test the size
             * of the Block Padding field.
             */
            while (s->block.compressed & 3) {
                if (b->in_pos == b->in_size)
                    return XZ_OK;

                if (b->in[b->in_pos++] != 0)
                    return XZ_DATA_ERROR;

                ++s->block.compressed;
            }

            s->sequence = SEQ_BLOCK_CHECK;

        case SEQ_BLOCK_CHECK:
            if (s->check_type == XZ_CHECK_CRC32) {
                ret = crc32_validate(s, b);
                if (ret != XZ_STREAM_END)
                    return ret;
            }
#ifdef XZ_DEC_ANY_CHECK
            else if (!check_skip(s, b)) {
                return XZ_OK;
            }
#endif

            s->sequence = SEQ_BLOCK_START;
            break;

        case SEQ_INDEX:
            ret = dec_index(s, b);
            if (ret != XZ_STREAM_END)
                return ret;

            s->sequence = SEQ_INDEX_PADDING;

        case SEQ_INDEX_PADDING:
            while ((s->index.size + (b->in_pos - s->in_start))
                    & 3) {
                if (b->in_pos == b->in_size) {
                    index_update(s, b);
                    return XZ_OK;
                }

                if (b->in[b->in_pos++] != 0)
                    return XZ_DATA_ERROR;
            }

            /* Finish the CRC32 value and Index size. */
            index_update(s, b);

            /* Compare the hashes to validate the Index field. */
            if (!memeq(&s->block.hash, &s->index.hash,
                    sizeof(s->block.hash)))
                return XZ_DATA_ERROR;

            s->sequence = SEQ_INDEX_CRC32;

        case SEQ_INDEX_CRC32:
            ret = crc32_validate(s, b);
            if (ret != XZ_STREAM_END)
                return ret;

            s->temp.size = STREAM_HEADER_SIZE;
            s->sequence = SEQ_STREAM_FOOTER;

        case SEQ_STREAM_FOOTER:
            if (!fill_temp(s, b))
                return XZ_OK;

            return dec_stream_footer(s);
        }
    }

    /* Never reached */
}

/*
 * xz_dec_run() is a wrapper for dec_main() to handle some special cases in
 * multi-call and single-call decoding.
 *
 * In multi-call mode, we must return XZ_BUF_ERROR when it seems clear that we
 * are not going to make any progress anymore. This is to prevent the caller
 * from calling us infinitely when the input file is truncated or otherwise
 * corrupt. Since zlib-style API allows that the caller fills the input buffer
 * only when the decoder doesn't produce any new output, we have to be careful
 * to avoid returning XZ_BUF_ERROR too easily: XZ_BUF_ERROR is returned only
 * after the second consecutive call to xz_dec_run() that makes no progress.
 *
 * In single-call mode, if we couldn't decode everything and no error
 * occurred, either the input is truncated or the output buffer is too small.
 * Since we know that the last input byte never produces any output, we know
 * that if all the input was consumed and decoding wasn't finished, the file
 * must be corrupt. Otherwise the output buffer has to be too small or the
 * file is corrupt in a way that decoding it produces too big output.
 *
 * If single-call decoding fails, we reset b->in_pos and b->out_pos back to
 * their original values. This is because with some filter chains there won't
 * be any valid uncompressed data in the output buffer unless the decoding
 * actually succeeds (that's the price to pay of using the output buffer as
 * the workspace).
 */
XZ_EXTERN enum xz_ret xz_dec_run(struct xz_dec *s, struct xz_buf *b)
{
    size_t in_start;
    size_t out_start;
    enum xz_ret ret;

    if (DEC_IS_SINGLE(s->mode))
        xz_dec_reset(s);

    in_start = b->in_pos;
    out_start = b->out_pos;
    ret = dec_main(s, b);

    if (DEC_IS_SINGLE(s->mode)) {
        if (ret == XZ_OK)
            ret = b->in_pos == b->in_size
                    ? XZ_DATA_ERROR : XZ_BUF_ERROR;

        if (ret != XZ_STREAM_END) {
            b->in_pos = in_start;
            b->out_pos = out_start;
        }

    } else if (ret == XZ_OK && in_start == b->in_pos
            && out_start == b->out_pos) {
        if (s->allow_buf_error)
            ret = XZ_BUF_ERROR;

        s->allow_buf_error = true;
    } else {
        s->allow_buf_error = false;
    }

    return ret;
}

XZ_EXTERN struct xz_dec *xz_dec_init(enum xz_mode mode, uint32_t dict_max)
{
    struct xz_dec *s = kmalloc(sizeof(*s), GFP_KERNEL);
    if (s == NULL)
        return NULL;

    s->mode = mode;

#ifdef XZ_DEC_BCJ
    s->bcj = xz_dec_bcj_create(DEC_IS_SINGLE(mode));
    if (s->bcj == NULL)
        goto error_bcj;
#endif

    s->lzma2 = xz_dec_lzma2_create(mode, dict_max);
    if (s->lzma2 == NULL)
        goto error_lzma2;

    xz_dec_reset(s);
    return s;

error_lzma2:
#ifdef XZ_DEC_BCJ
    xz_dec_bcj_end(s->bcj);
error_bcj:
#endif
    kfree(s);
    return NULL;
}

XZ_EXTERN void xz_dec_reset(struct xz_dec *s)
{
    s->sequence = SEQ_STREAM_HEADER;
    s->allow_buf_error = false;
    s->pos = 0;
    s->crc32 = 0;
    memzero(&s->block, sizeof(s->block));
    memzero(&s->index, sizeof(s->index));
    s->temp.pos = 0;
    s->temp.size = STREAM_HEADER_SIZE;
}

XZ_EXTERN void xz_dec_end(struct xz_dec *s)
{
    if (s != NULL) {
        xz_dec_lzma2_end(s->lzma2);
#ifdef XZ_DEC_BCJ
        xz_dec_bcj_end(s->bcj);
#endif
        kfree(s);
    }
}