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liblzma: Make EROFS LZMA decoder work when exact uncomp_size isn't known. 

The caller must still not specify an uncompressed size bigger
than the actual uncompressed size.

As a downside, this now needs the exact compressed size.
This commit is contained in:
Lasse Collin 2021-01-17 18:53:34 +02:00
parent 421b0aa352
commit 774cc0118b
2 changed files with 91 additions and 12 deletions
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23
src/liblzma/api/lzma/container.h
View File

@ -690,11 +690,22 @@ extern LZMA_API(lzma_ret) lzma_stream_buffer_decode(
* The special behavior of lzma_code() applies to lzma_erofs_encoder() only.
*
* \param strm Pointer to properly prepared lzma_stream
* \param comp_size Compressed size of the EROFS LZMA stream.
* The caller must somehow know this exactly.
* \param uncomp_size Uncompressed size of the EROFS LZMA stream.
* The caller must somehow know this. Note that
* while the EROFS LZMA decoder in XZ Embedded needs
* also the compressed size, the implementation in
* liblzma doesn't need to know the compressed size.
* If the exact uncompressed size isn't known, this
* can be set to a value that is at most as big as
* the exact uncompressed size would be, but then the
* next argument uncomp_size_is_exact must be false.
* \param uncomp_size_is_exact
* If true, uncomp_size must be exactly correct.
* This will improve error detection at the end of
* the stream. If the exact uncompressed size isn't
* known, this must be false. uncomp_size must still
* be at most as big as the exact uncompressed size
* is. Setting this to false when the exact size is
* known will work but error detection at the end of
* the stream will be weaker.
* \param dict_size LZMA dictionary size that was used when
* compressing the data. It is OK to use a bigger
* value too but liblzma will then allocate more
@ -705,4 +716,6 @@ extern LZMA_API(lzma_ret) lzma_stream_buffer_decode(
* dictionary than actually required.)
*/
extern LZMA_API(lzma_ret) lzma_erofs_decoder(
lzma_stream *strm, uint64_t uncomp_size, uint32_t dict_size);
lzma_stream *strm, uint64_t comp_size,
uint64_t uncomp_size, lzma_bool uncomp_size_is_exact,
uint32_t dict_size);

76
src/liblzma/common/erofs_decoder.c
View File

@ -18,12 +18,27 @@ typedef struct {
/// LZMA1 decoder
lzma_next_coder lzma;
/// Uncompressed size of the stream as given by the application
/// Compressed size of the stream as given by the application.
/// This must be exactly correct.
///
/// This will be decremented when input is read.
uint64_t comp_size;
/// Uncompressed size of the stream as given by the application.
/// This may be less than the actual uncompressed size if
/// uncomp_size_is_exact is false.
///
/// This will be decremented when output is produced.
lzma_vli uncomp_size;
/// LZMA dictionary size as given by the application
uint32_t dict_size;
/// If true, the exact uncompressed size is known. If false,
/// uncomp_size may be smaller than the real uncompressed size;
/// uncomp_size may never be bigger than the real uncompressed size.
bool uncomp_size_is_exact;
/// True once the first byte of the EROFS LZMA stream
/// has been processed.
bool props_decoded;
@ -38,6 +53,26 @@ erofs_decode(void *coder_ptr, const lzma_allocator *allocator,
{
lzma_erofs_coder *coder = coder_ptr;
// Remember the in start position so that we can update comp_size.
const size_t in_start = *in_pos;
// Remember the out start position so that we can update uncomp_size.
const size_t out_start = *out_pos;
// Limit the amount of input so that the decoder won't read more than
// comp_size. This is required when uncomp_size isn't exact because
// in that case the LZMA decoder will try to decode more input even
// when it has no output space (it can be looking for EOPM).
if (in_size - *in_pos > coder->comp_size)
in_size = *in_pos + (size_t)(coder->comp_size);
// When the exact uncompressed size isn't known, we must limit
// the available output space to prevent the LZMA decoder from
// trying to decode too much.
if (!coder->uncomp_size_is_exact
&& out_size - *out_pos > coder->uncomp_size)
out_size = *out_pos + (size_t)(coder->uncomp_size);
if (!coder->props_decoded) {
// There must be at least one byte of input to decode
// the properties byte.
@ -71,6 +106,7 @@ erofs_decode(void *coder_ptr, const lzma_allocator *allocator,
allocator, filters));
// Use a hack to set the uncompressed size.
if (coder->uncomp_size_is_exact)
lzma_lz_decoder_uncompressed(coder->lzma.coder,
coder->uncomp_size);
@ -88,9 +124,30 @@ erofs_decode(void *coder_ptr, const lzma_allocator *allocator,
}
// The rest is normal LZMA decoding.
return coder->lzma.code(coder->lzma.coder, allocator,
lzma_ret ret = coder->lzma.code(coder->lzma.coder, allocator,
in, in_pos, in_size,
out, out_pos, out_size, action);
// Update the remaining compressed size.
assert(coder->comp_size >= *in_pos - in_start);
coder->comp_size -= *in_pos - in_start;
if (!coder->uncomp_size_is_exact) {
// Update the amount of output remaining.
assert(coder->uncomp_size >= *out_pos - out_start);
coder->uncomp_size -= *out_pos - out_start;
// - We must not get LZMA_STREAM_END because the stream
// shouldn't have EOPM.
// - We must use uncomp_size to determine when to
// return LZMA_STREAM_END.
if (ret == LZMA_STREAM_END)
ret = LZMA_DATA_ERROR;
else if (coder->uncomp_size == 0)
ret = LZMA_STREAM_END;
}
return ret;
}
@ -106,7 +163,9 @@ erofs_decoder_end(void *coder_ptr, const lzma_allocator *allocator)
static lzma_ret
erofs_decoder_init(lzma_next_coder *next, const lzma_allocator *allocator,
uint64_t uncomp_size, uint32_t dict_size)
uint64_t comp_size,
uint64_t uncomp_size, bool uncomp_size_is_exact,
uint32_t dict_size)
{
lzma_next_coder_init(&erofs_decoder_init, next, allocator);
@ -124,10 +183,14 @@ erofs_decoder_init(lzma_next_coder *next, const lzma_allocator *allocator,
coder->lzma = LZMA_NEXT_CODER_INIT;
}
// The public API is uint64_t but the internal LZ decoder API uses
// lzma_vli.
if (uncomp_size > LZMA_VLI_MAX)
return LZMA_OPTIONS_ERROR;
coder->comp_size = comp_size;
coder->uncomp_size = uncomp_size;
coder->uncomp_size_is_exact = uncomp_size_is_exact;
coder->dict_size = dict_size;
coder->props_decoded = false;
@ -137,9 +200,12 @@ erofs_decoder_init(lzma_next_coder *next, const lzma_allocator *allocator,
extern LZMA_API(lzma_ret)
lzma_erofs_decoder(lzma_stream *strm, uint64_t uncomp_size, uint32_t dict_size)
lzma_erofs_decoder(lzma_stream *strm, uint64_t comp_size,
uint64_t uncomp_size, lzma_bool uncomp_size_is_exact,
uint32_t dict_size)
{
lzma_next_strm_init(erofs_decoder_init, strm, uncomp_size, dict_size);
lzma_next_strm_init(erofs_decoder_init, strm, comp_size,
uncomp_size, uncomp_size_is_exact, dict_size);
strm->internal->supported_actions[LZMA_RUN] = true;
strm->internal->supported_actions[LZMA_FINISH] = true;