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Merge pull request #2603 from terrelln/reduce-indices-fuzzer 

Bug fix & run overflow correction much more frequently in tests
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Nick Terrell 2021-05-03 19:24:55 -07:00 committed by GitHub
parent cc31bb8b66 34aff7ea06
commit 0b370e9da8
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5 changed files with 62 additions and 14 deletions
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6
lib/compress/zstd_compress.c
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@ -3803,9 +3803,9 @@ static void ZSTD_overflowCorrectIfNeeded(ZSTD_matchState_t* ms,
void const* ip,
void const* iend)
{
if (ZSTD_window_needOverflowCorrection(ms->window, iend)) {
U32 const maxDist = (U32)1 << params->cParams.windowLog;
U32 const cycleLog = ZSTD_cycleLog(params->cParams.chainLog, params->cParams.strategy);
U32 const cycleLog = ZSTD_cycleLog(params->cParams.chainLog, params->cParams.strategy);
U32 const maxDist = (U32)1 << params->cParams.windowLog;
if (ZSTD_window_needOverflowCorrection(ms->window, cycleLog, maxDist, ms->loadedDictEnd, ip, iend)) {
U32 const correction = ZSTD_window_correctOverflow(&ms->window, cycleLog, maxDist, ip);
ZSTD_STATIC_ASSERT(ZSTD_CHAINLOG_MAX <= 30);
ZSTD_STATIC_ASSERT(ZSTD_WINDOWLOG_MAX_32 <= 30);

61
lib/compress/zstd_compress_internal.h
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@ -895,15 +895,55 @@ MEM_STATIC ZSTD_dictMode_e ZSTD_matchState_dictMode(const ZSTD_matchState_t *ms)
ZSTD_noDict;
}
/* Defining this macro to non-zero tells zstd to run the overflow correction
* code much more frequently. This is very inefficient, and should only be
* used for tests and fuzzers.
*/
#ifndef ZSTD_WINDOW_OVERFLOW_CORRECT_FREQUENTLY
# ifdef FUZZING_BUILD_MODE_UNSAFE_FOR_PRODUCTION
# define ZSTD_WINDOW_OVERFLOW_CORRECT_FREQUENTLY 1
# else
# define ZSTD_WINDOW_OVERFLOW_CORRECT_FREQUENTLY 0
# endif
#endif
/**
* ZSTD_window_canOverflowCorrect():
* Returns non-zero if the indices are large enough for overflow correction
* to work correctly without impacting compression ratio.
*/
MEM_STATIC U32 ZSTD_window_canOverflowCorrect(ZSTD_window_t const window,
U32 cycleLog,
U32 maxDist,
U32 loadedDictEnd,
void const* src)
{
U32 const cycleSize = 1u << cycleLog;
U32 const curr = (U32)((BYTE const*)src - window.base);
U32 const minIndexToOverflowCorrect = cycleSize + MAX(maxDist, cycleSize);
U32 const indexLargeEnough = curr > minIndexToOverflowCorrect;
U32 const dictionaryInvalidated = curr > maxDist + loadedDictEnd;
return indexLargeEnough && dictionaryInvalidated;
}
/**
* ZSTD_window_needOverflowCorrection():
* Returns non-zero if the indices are getting too large and need overflow
* protection.
*/
MEM_STATIC U32 ZSTD_window_needOverflowCorrection(ZSTD_window_t const window,
U32 cycleLog,
U32 maxDist,
U32 loadedDictEnd,
void const* src,
void const* srcEnd)
{
U32 const curr = (U32)((BYTE const*)srcEnd - window.base);
if (ZSTD_WINDOW_OVERFLOW_CORRECT_FREQUENTLY) {
if (ZSTD_window_canOverflowCorrect(window, cycleLog, maxDist, loadedDictEnd, src)) {
return 1;
}
}
return curr > ZSTD_CURRENT_MAX;
}
@ -915,7 +955,6 @@ MEM_STATIC U32 ZSTD_window_needOverflowCorrection(ZSTD_window_t const window,
*
* The least significant cycleLog bits of the indices must remain the same,
* which may be 0. Every index up to maxDist in the past must be valid.
* NOTE: (maxDist & cycleMask) must be zero.
*/
MEM_STATIC U32 ZSTD_window_correctOverflow(ZSTD_window_t* window, U32 cycleLog,
U32 maxDist, void const* src)
@ -939,17 +978,25 @@ MEM_STATIC U32 ZSTD_window_correctOverflow(ZSTD_window_t* window, U32 cycleLog,
* 3. (cctx->lowLimit + 1<<windowLog) < 1<<32:
* windowLog <= 31 ==> 3<<29 + 1<<windowLog < 7<<29 < 1<<32.
*/
U32 const cycleMask = (1U << cycleLog) - 1;
U32 const cycleSize = 1u << cycleLog;
U32 const cycleMask = cycleSize - 1;
U32 const curr = (U32)((BYTE const*)src - window->base);
U32 const currentCycle0 = curr & cycleMask;
/* Exclude zero so that newCurrent - maxDist >= 1. */
U32 const currentCycle1 = currentCycle0 == 0 ? (1U << cycleLog) : currentCycle0;
U32 const newCurrent = currentCycle1 + maxDist;
U32 const currentCycle1 = currentCycle0 == 0 ? cycleSize : currentCycle0;
U32 const newCurrent = currentCycle1 + MAX(maxDist, cycleSize);
U32 const correction = curr - newCurrent;
assert((maxDist & cycleMask) == 0);
/* maxDist must be a power of two so that:
* (newCurrent & cycleMask) == (curr & cycleMask)
* This is required to not corrupt the chains / binary tree.
*/
assert((maxDist & (maxDist - 1)) == 0);
assert((curr & cycleMask) == (newCurrent & cycleMask));
assert(curr > newCurrent);
/* Loose bound, should be around 1<<29 (see above) */
assert(correction > 1<<28);
if (!ZSTD_WINDOW_OVERFLOW_CORRECT_FREQUENTLY) {
/* Loose bound, should be around 1<<29 (see above) */
assert(correction > 1<<28);
}
window->base += correction;
window->dictBase += correction;

2
lib/compress/zstd_ldm.c
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@ -500,7 +500,7 @@ size_t ZSTD_ldm_generateSequences(
assert(chunkStart < iend);
/* 1. Perform overflow correction if necessary. */
if (ZSTD_window_needOverflowCorrection(ldmState->window, chunkEnd)) {
if (ZSTD_window_needOverflowCorrection(ldmState->window, 0, maxDist, ldmState->loadedDictEnd, chunkStart, chunkEnd)) {
U32 const ldmHSize = 1U << params->hashLog;
U32 const correction = ZSTD_window_correctOverflow(
&ldmState->window, /* cycleLog */ 0, maxDist, chunkStart);

3
tests/Makefile
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@ -28,7 +28,8 @@ DEBUGLEVEL ?= 1
export DEBUGLEVEL # transmit value to sub-makefiles
DEBUGFLAGS = -g -DDEBUGLEVEL=$(DEBUGLEVEL)
CPPFLAGS += -I$(ZSTDDIR) -I$(ZSTDDIR)/common -I$(ZSTDDIR)/compress \
-I$(ZSTDDIR)/dictBuilder -I$(ZSTDDIR)/deprecated -I$(PRGDIR)
-I$(ZSTDDIR)/dictBuilder -I$(ZSTDDIR)/deprecated -I$(PRGDIR) \
-DZSTD_WINDOW_OVERFLOW_CORRECT_FREQUENTLY=1
ifeq ($(OS),Windows_NT) # MinGW assumed
CPPFLAGS += -D__USE_MINGW_ANSI_STDIO # compatibility with %zu formatting
endif