ddidderr/zstd-rs
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Fixed a nasty corruption bug

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recently introduce into the new dictionary mode.
The bug could be reproduced with this command :
./zstreamtest -v --opaqueapi --no-big-tests -s4092 -t639

error was in function ZSTD_count_2segments() :
the beginning of the 2nd segment corresponds to prefixStart
and not the beginning of the current block (istart == src).
This would result in comparing the wrong byte.
This commit is contained in:
Yann Collet
2018-06-01 18:54:34 -07:00
parent 143fc9ff6c
commit 2108decb41
6 changed files with 58 additions and 40 deletions
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lib/compress/zstd_fast.c
+7 -7
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@@ -54,7 +54,7 @@ size_t ZSTD_compressBlock_fast_generic(
const BYTE* ip = istart;
const BYTE* anchor = istart;
const U32 prefixLowestIndex = ms->window.dictLimit;
const BYTE* const prefixLowest = base + prefixLowestIndex;
const BYTE* const prefixStart = base + prefixLowestIndex;
const BYTE* const iend = istart + srcSize;
const BYTE* const ilimit = iend - HASH_READ_SIZE;
U32 offset_1=rep[0], offset_2=rep[1];
@@ -74,7 +74,7 @@ size_t ZSTD_compressBlock_fast_generic(
const U32 dictIndexDelta = dictMode == ZSTD_dictMatchState ?
prefixLowestIndex - (U32)(dictEnd - dictBase) :
0;
const U32 dictAndPrefixLength = (U32)(ip - prefixLowest + dictEnd - dictLowest);
const U32 dictAndPrefixLength = (U32)(ip - prefixStart + dictEnd - dictLowest);
assert(dictMode == ZSTD_noDict || dictMode == ZSTD_dictMatchState);
@@ -86,7 +86,7 @@ size_t ZSTD_compressBlock_fast_generic(
/* init */
ip += (dictAndPrefixLength == 0);
if (dictMode == ZSTD_noDict) {
U32 const maxRep = (U32)(ip - prefixLowest);
U32 const maxRep = (U32)(ip - prefixStart);
if (offset_2 > maxRep) offsetSaved = offset_2, offset_2 = 0;
if (offset_1 > maxRep) offsetSaved = offset_1, offset_1 = 0;
}
@@ -115,7 +115,7 @@ size_t ZSTD_compressBlock_fast_generic(
&& ((U32)((prefixLowestIndex-1) - repIndex) >= 3 /* intentional underflow */)
&& (MEM_read32(repMatch) == MEM_read32(ip+1)) ) {
const BYTE* repMatchEnd = repIndex < prefixLowestIndex ? dictEnd : iend;
mLength = ZSTD_count_2segments(ip+1+4, repMatch+4, iend, repMatchEnd, istart) + 4;
mLength = ZSTD_count_2segments(ip+1+4, repMatch+4, iend, repMatchEnd, prefixStart) + 4;
ip++;
ZSTD_storeSeq(seqStore, ip-anchor, anchor, 0, mLength-MINMATCH);
} else if ( dictMode == ZSTD_noDict
@@ -136,7 +136,7 @@ size_t ZSTD_compressBlock_fast_generic(
} else {
/* found a dict match */
U32 const offset = (U32)(current-dictMatchIndex-dictIndexDelta);
mLength = ZSTD_count_2segments(ip+4, dictMatch+4, iend, dictEnd, istart) + 4;
mLength = ZSTD_count_2segments(ip+4, dictMatch+4, iend, dictEnd, prefixStart) + 4;
while (((ip>anchor) & (dictMatch>dictLowest))
&& (ip[-1] == dictMatch[-1])) {
ip--; dictMatch--; mLength++;
@@ -154,7 +154,7 @@ size_t ZSTD_compressBlock_fast_generic(
/* found a regular match */
U32 const offset = (U32)(ip-match);
mLength = ZSTD_count(ip+4, match+4, iend) + 4;
while (((ip>anchor) & (match>prefixLowest))
while (((ip>anchor) & (match>prefixStart))
&& (ip[-1] == match[-1])) { ip--; match--; mLength++; } /* catch up */
offset_2 = offset_1;
offset_1 = offset;
@@ -181,7 +181,7 @@ size_t ZSTD_compressBlock_fast_generic(
if ( ((U32)((prefixLowestIndex-1) - (U32)repIndex2) >= 3 /* intentional overflow */)
&& (MEM_read32(repMatch2) == MEM_read32(ip)) ) {
const BYTE* const repEnd2 = repIndex2 < prefixLowestIndex ? dictEnd : iend;
size_t const repLength2 = ZSTD_count_2segments(ip+4, repMatch2+4, iend, repEnd2, istart) + 4;
size_t const repLength2 = ZSTD_count_2segments(ip+4, repMatch2+4, iend, repEnd2, prefixStart) + 4;
U32 tmpOffset = offset_2; offset_2 = offset_1; offset_1 = tmpOffset; /* swap offset_2 <=> offset_1 */
ZSTD_storeSeq(seqStore, 0, anchor, 0, repLength2-MINMATCH);
hashTable[ZSTD_hashPtr(ip, hlog, mls)] = current2;