/* * .xz Stream decoder * * Author: Lasse Collin <lasse.collin@tukaani.org> * * 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); } }