diff options
| -rw-r--r-- | lib/lz4hc.c | 65 |
1 files changed, 45 insertions, 20 deletions
diff --git a/lib/lz4hc.c b/lib/lz4hc.c index a0b8c48..596888a 100644 --- a/lib/lz4hc.c +++ b/lib/lz4hc.c @@ -218,6 +218,16 @@ LZ4HC_reverseCountPattern(const BYTE* ip, const BYTE* const iLow, U32 pattern) return (unsigned)(iStart - ip); } +/* LZ4HC_protectDictEnd() : + * Checks if the match is in the last 3 bytes of the dictionary, so reading the + * 4 byte MINMATCH would overflow. + * @returns true if the match index is okay. + */ +static int LZ4HC_protectDictEnd(U32 const dictLimit, U32 const matchIndex) +{ + return ((U32)((dictLimit - 1) - matchIndex) >= 3); +} + typedef enum { rep_untested, rep_not, rep_confirmed } repeat_state_e; typedef enum { favorCompressionRatio=0, favorDecompressionSpeed } HCfavor_e; @@ -304,7 +314,7 @@ LZ4HC_InsertAndGetWiderMatch ( if (matchIndex + (U32)longest <= ipIndex) { U32 distanceToNextMatch = 1; int pos; - for (pos = 0; pos <= longest - MINMATCH; pos++) { + for (pos = 0; pos <= longest - MINMATCH; ++pos) { U32 const candidateDist = DELTANEXTU16(chainTable, matchIndex + (U32)pos); if (candidateDist > distanceToNextMatch) { distanceToNextMatch = candidateDist; @@ -314,7 +324,8 @@ LZ4HC_InsertAndGetWiderMatch ( if (distanceToNextMatch > matchIndex) break; /* avoid overflow */ matchIndex -= distanceToNextMatch; continue; - } } } + } + } } { U32 const distNextMatch = DELTANEXTU16(chainTable, matchIndex); if (patternAnalysis && distNextMatch==1 && matchChainPos==0) { @@ -328,7 +339,8 @@ LZ4HC_InsertAndGetWiderMatch ( } else { repeat = rep_not; } } - if ( (repeat == rep_confirmed) && (matchCandidateIdx >= lowestMatchIndex) ) { + if ( (repeat == rep_confirmed) && (matchCandidateIdx >= lowestMatchIndex) + && LZ4HC_protectDictEnd(dictLimit, matchCandidateIdx) ) { const int extDict = matchCandidateIdx < dictLimit; const BYTE* const matchPtr = (extDict ? dictBase : base) + matchCandidateIdx; if (LZ4_read32(matchPtr) == pattern) { /* good candidate */ @@ -348,27 +360,40 @@ LZ4HC_InsertAndGetWiderMatch ( } /* Limit backLength not go further than lowestMatchIndex */ backLength = matchCandidateIdx - MAX(matchCandidateIdx - (U32)backLength, lowestMatchIndex); + assert(matchCandidateIdx - backLength >= lowestMatchIndex); currentSegmentLength = backLength + forwardPatternLength; - + /* Adjust to end of pattern if the source pattern fits, otherwise the beginning of the pattern */ if ( (currentSegmentLength >= srcPatternLength) /* current pattern segment large enough to contain full srcPatternLength */ && (forwardPatternLength <= srcPatternLength) ) { /* haven't reached this position yet */ - matchIndex = matchCandidateIdx + (U32)forwardPatternLength - (U32)srcPatternLength; /* best position, full pattern, might be followed by more match */ + U32 const newMatchIndex = matchCandidateIdx + (U32)forwardPatternLength - (U32)srcPatternLength; /* best position, full pattern, might be followed by more match */ + if (LZ4HC_protectDictEnd(dictLimit, newMatchIndex)) + matchIndex = newMatchIndex; + else { + /* Can only happen if started in the prefix */ + assert(newMatchIndex >= dictLimit - 3 && newMatchIndex < dictLimit && !extDict); + matchIndex = dictLimit; + } } else { - matchIndex = matchCandidateIdx - (U32)backLength; /* farthest position in current segment, will find a match of length currentSegmentLength + maybe some back */ - if (lookBackLength==0) { /* no back possible */ - size_t const maxML = MIN(currentSegmentLength, srcPatternLength); - if ((size_t)longest < maxML) { - assert(base + matchIndex < ip); - if (ip - (base+matchIndex) > LZ4_DISTANCE_MAX) break; - assert(maxML < 2 GB); - longest = (int)maxML; - *matchpos = base + matchIndex; /* virtual pos, relative to ip, to retrieve offset */ - *startpos = ip; - } - { U32 const distToNextPattern = DELTANEXTU16(chainTable, matchIndex); - if (distToNextPattern > matchIndex) break; /* avoid overflow */ - matchIndex -= distToNextPattern; - } } } } + U32 const newMatchIndex = matchCandidateIdx - (U32)backLength; /* farthest position in current segment, will find a match of length currentSegmentLength + maybe some back */ + if (!LZ4HC_protectDictEnd(dictLimit, newMatchIndex)) { + assert(newMatchIndex >= dictLimit - 3 && newMatchIndex < dictLimit && !extDict); + matchIndex = dictLimit; + } else { + matchIndex = newMatchIndex; + if (lookBackLength==0) { /* no back possible */ + size_t const maxML = MIN(currentSegmentLength, srcPatternLength); + if ((size_t)longest < maxML) { + assert(base + matchIndex < ip); + if (ip - (base+matchIndex) > LZ4_DISTANCE_MAX) break; + assert(maxML < 2 GB); + longest = (int)maxML; + *matchpos = base + matchIndex; /* virtual pos, relative to ip, to retrieve offset */ + *startpos = ip; + } + { U32 const distToNextPattern = DELTANEXTU16(chainTable, matchIndex); + if (distToNextPattern > matchIndex) break; /* avoid overflow */ + matchIndex -= distToNextPattern; + } } } } } continue; } } } } /* PA optimization */ |