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

diff --git a/src/liblzma/common/alone_decoder.c b/src/liblzma/common/alone_decoder.c
index 678c79e6543339219a19aafaf387c4af463f727d..c25112e6875f5e061bc185608fb65b0a08df611e 100644 (file)
--- 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 70d0d2a0ffa4deff7bbcb3bff52a3a61b4118d26..f666fc3823e1c59b04526e21aa73bf922a67e83f 100644 (file)
--- 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 ae6c3e78642ca52346265f6da4139bd0e92151c3..35c895fd14c28fce7d32de754d5f75160a037f68 100644 (file)
--- 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