// SPDX-License-Identifier: 0BSD
/*
* .xz Stream decoder
*
* Author: Lasse Collin <[email protected]>
*/
#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.
*/
if (s->temp.buf[HEADER_MAGIC_SIZE + 1] > XZ_CHECK_MAX)
return XZ_OPTIONS_ERROR;
s->check_type = s->temp.buf[HEADER_MAGIC_SIZE + 1];
#ifdef XZ_DEC_ANY_CHECK
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;
fallthrough;
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;
fallthrough;
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;
fallthrough;
case SEQ_BLOCK_UNCOMPRESS:
ret = dec_block(s, b);
if (ret != XZ_STREAM_END)
return ret;
s->sequence = SEQ_BLOCK_PADDING;
fallthrough;
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;
fallthrough;
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;
fallthrough;
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;
fallthrough;
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;
fallthrough;
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).
*/
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;
}
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;
}
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;
}
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);
}
}
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