From 9271a3eb0e022b23e8712154be851d0afe4c02e4 Mon Sep 17 00:00:00 2001 From: Lasse Collin Date: Fri, 5 Apr 2013 19:34:09 +0300 Subject: [PATCH] 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 --- src/liblzma/common/alone_decoder.c | 22 ++++++++++++++-------- src/liblzma/common/alone_decoder.h | 5 +++-- src/liblzma/common/auto_decoder.c | 2 +- 3 files changed, 18 insertions(+), 11 deletions(-) diff --git a/src/liblzma/common/alone_decoder.c b/src/liblzma/common/alone_decoder.c index 678c79e6..c25112e6 100644 --- a/src/liblzma/common/alone_decoder.c +++ b/src/liblzma/common/alone_decoder.c @@ -26,6 +26,11 @@ struct lzma_coder_s { SEQ_CODE, } 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 size_t pos; @@ -68,13 +73,13 @@ alone_decode(lzma_coder *coder, |= (size_t)(in[*in_pos]) << (coder->pos * 8); 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: // We allow only dictionary sizes that are // 2^n or 2^n + 2^(n-1). LZMA_Alone created // only files with 2^n, but accepts any - // dictionary size. If someone complains, this - // will be reconsidered. + // dictionary size. uint32_t d = coder->options.dict_size - 1; d |= d >> 2; d |= d >> 3; @@ -103,9 +108,9 @@ alone_decode(lzma_coder *coder, // Another hack to ditch false positives: Assume that // if the uncompressed size is known, it must be less - // than 256 GiB. Again, if someone complains, this - // will be reconsidered. - if (coder->uncompressed_size != LZMA_VLI_UNKNOWN + // than 256 GiB. + if (coder->picky + && coder->uncompressed_size != LZMA_VLI_UNKNOWN && coder->uncompressed_size >= (LZMA_VLI_C(1) << 38)) return LZMA_FORMAT_ERROR; @@ -189,7 +194,7 @@ alone_decoder_memconfig(lzma_coder *coder, uint64_t *memusage, extern lzma_ret 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); @@ -208,6 +213,7 @@ lzma_alone_decoder_init(lzma_next_coder *next, lzma_allocator *allocator, } next->coder->sequence = SEQ_PROPERTIES; + next->coder->picky = picky; next->coder->pos = 0; next->coder->options.dict_size = 0; 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) 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_FINISH] = true; diff --git a/src/liblzma/common/alone_decoder.h b/src/liblzma/common/alone_decoder.h index 70d0d2a0..f666fc38 100644 --- a/src/liblzma/common/alone_decoder.h +++ b/src/liblzma/common/alone_decoder.h @@ -16,7 +16,8 @@ #include "common.h" -extern lzma_ret lzma_alone_decoder_init(lzma_next_coder *next, - lzma_allocator *allocator, uint64_t memlimit); +extern lzma_ret lzma_alone_decoder_init( + lzma_next_coder *next, lzma_allocator *allocator, + uint64_t memlimit, bool picky); #endif diff --git a/src/liblzma/common/auto_decoder.c b/src/liblzma/common/auto_decoder.c index ae6c3e78..35c895fd 100644 --- a/src/liblzma/common/auto_decoder.c +++ b/src/liblzma/common/auto_decoder.c @@ -54,7 +54,7 @@ auto_decode(lzma_coder *coder, lzma_allocator *allocator, coder->memlimit, coder->flags)); } else { return_if_error(lzma_alone_decoder_init(&coder->next, - allocator, coder->memlimit)); + allocator, coder->memlimit, true)); // If the application wants to know about missing // integrity check or about the check in general, we