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liblzma: Be less picky in lzma_alone_decoder(). 

To avoid false positives when detecting .lzma files,
rare values in dictionary size and uncompressed size fields
were rejected. They will still be rejected if .lzma files
are decoded with lzma_auto_decoder(), but when using
lzma_alone_decoder() directly, such files will now be accepted.
Hopefully this is an OK compromise.

This doesn't affect xz because xz still has its own file
format detection code. This does affect lzmadec though.
So after this commit lzmadec will accept files that xz or
xz-emulating-lzma doesn't.

NOTE: lzma_alone_decoder() still won't decode all .lzma files
because liblzma's LZMA decoder doesn't support lc + lp > 4.

Reported here:
http://sourceforge.net/projects/lzmautils/forums/forum/708858/topic/7068827

Conflicts:
	src/liblzma/common/alone_decoder.c
	src/liblzma/common/alone_decoder.h
This commit is contained in:
Lasse Collin 2013-04-05 19:34:09 +03:00
parent 211b931cee
commit 9271a3eb0e
3 changed files with 18 additions and 11 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

22
src/liblzma/common/alone_decoder.c
View File

@ -26,6 +26,11 @@ struct lzma_coder_s {
SEQ_CODE, SEQ_CODE,
} sequence; } sequence;
/// If true, reject files that are unlikely to be .lzma files.
/// If false, more non-.lzma files get accepted and will give
/// LZMA_DATA_ERROR either immediately or after a few output bytes.
bool picky;
/// Position in the header fields /// Position in the header fields
size_t pos; size_t pos;
@ -68,13 +73,13 @@ alone_decode(lzma_coder *coder,
|= (size_t)(in[*in_pos]) << (coder->pos * 8); |= (size_t)(in[*in_pos]) << (coder->pos * 8);
if (++coder->pos == 4) { if (++coder->pos == 4) {
if (coder->options.dict_size != UINT32_MAX) { if (coder->picky && coder->options.dict_size
!= UINT32_MAX) {
// A hack to ditch tons of false positives: // A hack to ditch tons of false positives:
// We allow only dictionary sizes that are // We allow only dictionary sizes that are
// 2^n or 2^n + 2^(n-1). LZMA_Alone created // 2^n or 2^n + 2^(n-1). LZMA_Alone created
// only files with 2^n, but accepts any // only files with 2^n, but accepts any
// dictionary size. If someone complains, this // dictionary size.
// will be reconsidered.
uint32_t d = coder->options.dict_size - 1; uint32_t d = coder->options.dict_size - 1;
d |= d >> 2; d |= d >> 2;
d |= d >> 3; d |= d >> 3;
@ -103,9 +108,9 @@ alone_decode(lzma_coder *coder,
// Another hack to ditch false positives: Assume that // Another hack to ditch false positives: Assume that
// if the uncompressed size is known, it must be less // if the uncompressed size is known, it must be less
// than 256 GiB. Again, if someone complains, this // than 256 GiB.
// will be reconsidered. if (coder->picky
if (coder->uncompressed_size != LZMA_VLI_UNKNOWN && coder->uncompressed_size != LZMA_VLI_UNKNOWN
&& coder->uncompressed_size && coder->uncompressed_size
>= (LZMA_VLI_C(1) << 38)) >= (LZMA_VLI_C(1) << 38))
return LZMA_FORMAT_ERROR; return LZMA_FORMAT_ERROR;
@ -189,7 +194,7 @@ alone_decoder_memconfig(lzma_coder *coder, uint64_t *memusage,
extern lzma_ret extern lzma_ret
lzma_alone_decoder_init(lzma_next_coder *next, lzma_allocator *allocator, lzma_alone_decoder_init(lzma_next_coder *next, lzma_allocator *allocator,
uint64_t memlimit) uint64_t memlimit, bool picky)
{ {
lzma_next_coder_init(&lzma_alone_decoder_init, next, allocator); lzma_next_coder_init(&lzma_alone_decoder_init, next, allocator);
@ -208,6 +213,7 @@ lzma_alone_decoder_init(lzma_next_coder *next, lzma_allocator *allocator,
} }
next->coder->sequence = SEQ_PROPERTIES; next->coder->sequence = SEQ_PROPERTIES;
next->coder->picky = picky;
next->coder->pos = 0; next->coder->pos = 0;
next->coder->options.dict_size = 0; next->coder->options.dict_size = 0;
next->coder->options.preset_dict = NULL; next->coder->options.preset_dict = NULL;
@ -223,7 +229,7 @@ lzma_alone_decoder_init(lzma_next_coder *next, lzma_allocator *allocator,
extern LZMA_API(lzma_ret) extern LZMA_API(lzma_ret)
lzma_alone_decoder(lzma_stream *strm, uint64_t memlimit) lzma_alone_decoder(lzma_stream *strm, uint64_t memlimit)
{ {
lzma_next_strm_init(lzma_alone_decoder_init, strm, memlimit); lzma_next_strm_init(lzma_alone_decoder_init, strm, memlimit, false);
strm->internal->supported_actions[LZMA_RUN] = true; strm->internal->supported_actions[LZMA_RUN] = true;
strm->internal->supported_actions[LZMA_FINISH] = true; strm->internal->supported_actions[LZMA_FINISH] = true;

5
src/liblzma/common/alone_decoder.h
View File

@ -16,7 +16,8 @@
#include "common.h" #include "common.h"
extern lzma_ret lzma_alone_decoder_init(lzma_next_coder *next, extern lzma_ret lzma_alone_decoder_init(
lzma_allocator *allocator, uint64_t memlimit); lzma_next_coder *next, lzma_allocator *allocator,
uint64_t memlimit, bool picky);
#endif #endif

2
src/liblzma/common/auto_decoder.c
View File

@ -54,7 +54,7 @@ auto_decode(lzma_coder *coder, lzma_allocator *allocator,
coder->memlimit, coder->flags)); coder->memlimit, coder->flags));
} else { } else {
return_if_error(lzma_alone_decoder_init(&coder->next, return_if_error(lzma_alone_decoder_init(&coder->next,
allocator, coder->memlimit)); allocator, coder->memlimit, true));
// If the application wants to know about missing // If the application wants to know about missing
// integrity check or about the check in general, we // integrity check or about the check in general, we