liblzma: Add optional autodetection of LZMA end marker.

Turns out that this is needed for .lzma files as the spec in
LZMA SDK says that end marker may be present even if the size
is stored in the header. Such files are rare but exist in the
real world. The code in liblzma is so old that the spec didn't
exist in LZMA SDK back then and I had understood that such
files weren't possible (the lzma tool in LZMA SDK didn't
create such files).

This modifies the internal API so that LZMA decoder can be told
if EOPM is allowed even when the uncompressed size is known.
It's allowed with .lzma and not with other uses.

Thanks to Karl Beldan for reporting the problem.

1 files changed, 70 insertions, 29 deletions

diff --git a/src/liblzma/lzma/lzma_decoder.c b/src/liblzma/lzma/lzma_decoder.c
index e605a0a9..140a44f1 100644
--- a/src/liblzma/lzma/lzma_decoder.c
+++ b/src/liblzma/lzma/lzma_decoder.c
@@ -238,6 +238,11 @@ typedef struct {
 	/// payload marker is expected.
 	lzma_vli uncompressed_size;
 
+	/// True if end of payload marker (EOPM) is allowed even when
+	/// uncompressed_size is known; false if EOPM must not be present.
+	/// This is ignored if uncompressed_size == LZMA_VLI_UNKNOWN.
+	bool allow_eopm;
+
 	////////////////////////////////
 	// State of incomplete symbol //
 	////////////////////////////////
@@ -343,12 +348,19 @@ lzma_decode(void *coder_ptr, lzma_dict *restrict dictptr,
 
 	lzma_ret ret = LZMA_OK;
 
-	// If uncompressed size is known, there must be no end of payload
-	// marker.
-	const bool no_eopm = coder->uncompressed_size
-			!= LZMA_VLI_UNKNOWN;
-	if (no_eopm && coder->uncompressed_size < dict.limit - dict.pos)
+	// EOPM is always required (not just allowed) when
+	// the uncompressed size isn't known.
+	bool eopm_allowed = coder->uncompressed_size == LZMA_VLI_UNKNOWN;
+
+	// If uncompressed size is known and there is enough output space
+	// to decode all the data, limit the available buffer space so that
+	// the main loop won't try to decode past the end of the stream.
+	bool might_finish_without_eopm = false;
+	if (coder->uncompressed_size != LZMA_VLI_UNKNOWN
+			&& coder->uncompressed_size <= dict.limit - dict.pos) {
 		dict.limit = dict.pos + (size_t)(coder->uncompressed_size);
+		might_finish_without_eopm = true;
+	}
 
 	// The main decoder loop. The "switch" is used to restart the decoder at
 	// correct location. Once restarted, the "switch" is no longer used.
@@ -361,8 +373,32 @@ lzma_decode(void *coder_ptr, lzma_dict *restrict dictptr,
 
 	case SEQ_NORMALIZE:
 	case SEQ_IS_MATCH:
-		if (unlikely(no_eopm && dict.pos == dict.limit))
-			break;
+		if (unlikely(might_finish_without_eopm
+				&& dict.pos == dict.limit)) {
+			// In rare cases there is a useless byte that needs
+			// to be read anyway.
+			rc_normalize(SEQ_NORMALIZE);
+
+			// If the range decoder state is such that we can
+			// be at the end of the LZMA stream, then the
+			// decoding is finished.
+			if (rc_is_finished(rc)) {
+				ret = LZMA_STREAM_END;
+				goto out;
+			}
+
+			// If the caller hasn't allowed EOPM to be present
+			// together with known uncompressed size, then the
+			// LZMA stream is corrupt.
+			if (!coder->allow_eopm) {
+				ret = LZMA_DATA_ERROR;
+				goto out;
+			}
+
+			// Otherwise continue decoding with the expectation
+			// that the next LZMA symbol is EOPM.
+			eopm_allowed = true;
+		}
 
 		rc_if_0(coder->is_match[state][pos_state], SEQ_IS_MATCH) {
 			rc_update_0(coder->is_match[state][pos_state]);
@@ -658,11 +694,18 @@ lzma_decode(void *coder_ptr, lzma_dict *restrict dictptr,
 
 					if (rep0 == UINT32_MAX) {
 						// End of payload marker was
-						// found. It must not be
-						// present if uncompressed
-						// size is known.
-						if (coder->uncompressed_size
-						!= LZMA_VLI_UNKNOWN) {
+						// found. It may only be
+						// present if
+						//   - uncompressed size is
+						//     unknown or
+						//   - after known uncompressed
+						//     size amount of bytes has
+						//     been decompressed and
+						//     caller has indicated
+						//     that EOPM might be used
+						//     (it's not allowed in
+						//     LZMA2).
+						if (!eopm_allowed) {
 							ret = LZMA_DATA_ERROR;
 							goto out;
 						}
@@ -671,7 +714,9 @@ lzma_decode(void *coder_ptr, lzma_dict *restrict dictptr,
 						// LZMA1 stream with
 						// end-of-payload marker.
 						rc_normalize(SEQ_EOPM);
-						ret = LZMA_STREAM_END;
+						ret = rc_is_finished(rc)
+							? LZMA_STREAM_END
+							: LZMA_DATA_ERROR;
 						goto out;
 					}
 				}
@@ -793,9 +838,6 @@ lzma_decode(void *coder_ptr, lzma_dict *restrict dictptr,
 		}
 	}
 
-	rc_normalize(SEQ_NORMALIZE);
-	coder->sequence = SEQ_IS_MATCH;
-
 out:
 	// Save state
 
@@ -822,24 +864,21 @@ out:
 	if (coder->uncompressed_size != LZMA_VLI_UNKNOWN) {
 		coder->uncompressed_size -= dict.pos - dict_start;
 
-		// Since there cannot be end of payload marker if the
-		// uncompressed size was known, we check here if we
-		// finished decoding.
+		// If we have gotten all the output but the decoder wants
+		// to write more output, the file is corrupt. There are
+		// three SEQ values where output is produced.
 		if (coder->uncompressed_size == 0 && ret == LZMA_OK
-				&& coder->sequence != SEQ_NORMALIZE)
-			ret = coder->sequence == SEQ_IS_MATCH
-					? LZMA_STREAM_END : LZMA_DATA_ERROR;
+				&& (coder->sequence == SEQ_LITERAL_WRITE
+					|| coder->sequence == SEQ_SHORTREP
+					|| coder->sequence == SEQ_COPY))
+			ret = LZMA_DATA_ERROR;
 	}
 
-	// We can do an additional check in the range decoder to catch some
-	// corrupted files.
 	if (ret == LZMA_STREAM_END) {
-		if (!rc_is_finished(coder->rc))
-			ret = LZMA_DATA_ERROR;
-
 		// Reset the range decoder so that it is ready to reinitialize
 		// for a new LZMA2 chunk.
 		rc_reset(coder->rc);
+		coder->sequence = SEQ_IS_MATCH;
 	}
 
 	return ret;
@@ -848,10 +887,12 @@ out:
 
 
 static void
-lzma_decoder_uncompressed(void *coder_ptr, lzma_vli uncompressed_size)
+lzma_decoder_uncompressed(void *coder_ptr, lzma_vli uncompressed_size,
+		bool allow_eopm)
 {
 	lzma_lzma1_decoder *coder = coder_ptr;
 	coder->uncompressed_size = uncompressed_size;
+	coder->allow_eopm = allow_eopm;
 }
 
 
@@ -977,7 +1018,7 @@ lzma_decoder_init(lzma_lz_decoder *lz, const lzma_allocator *allocator,
 			lz, allocator, options, lz_options));
 
 	lzma_decoder_reset(lz->coder, options);
-	lzma_decoder_uncompressed(lz->coder, LZMA_VLI_UNKNOWN);
+	lzma_decoder_uncompressed(lz->coder, LZMA_VLI_UNKNOWN, true);
 
 	return LZMA_OK;
 }