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Merge pull request #2869 from felixhandte/oss-fuzz-fix-41005

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Determinism: Avoid Mapping Window into Reserved Indices during Reduction
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Felix Handte 2021-11-18 10:11:48 -05:00 committed by GitHub
commit c2c6a4ab40
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1 changed files with 22 additions and 10 deletions
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32
lib/compress/zstd_compress_internal.h
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@ -982,7 +982,9 @@ MEM_STATIC U32 ZSTD_window_canOverflowCorrect(ZSTD_window_t const window,
{ {
U32 const cycleSize = 1u << cycleLog; U32 const cycleSize = 1u << cycleLog;
U32 const curr = (U32)((BYTE const*)src - window.base); U32 const curr = (U32)((BYTE const*)src - window.base);
U32 const minIndexToOverflowCorrect = cycleSize + MAX(maxDist, cycleSize); U32 const minIndexToOverflowCorrect = cycleSize
+ MAX(maxDist, cycleSize)
+ ZSTD_WINDOW_START_INDEX;
/* Adjust the min index to backoff the overflow correction frequency, /* Adjust the min index to backoff the overflow correction frequency,
* so we don't waste too much CPU in overflow correction. If this * so we don't waste too much CPU in overflow correction. If this
@ -1057,10 +1059,14 @@ MEM_STATIC U32 ZSTD_window_correctOverflow(ZSTD_window_t* window, U32 cycleLog,
U32 const cycleSize = 1u << cycleLog; U32 const cycleSize = 1u << cycleLog;
U32 const cycleMask = cycleSize - 1; U32 const cycleMask = cycleSize - 1;
U32 const curr = (U32)((BYTE const*)src - window->base); U32 const curr = (U32)((BYTE const*)src - window->base);
U32 const currentCycle0 = curr & cycleMask; U32 const currentCycle = curr & cycleMask;
/* Exclude zero so that newCurrent - maxDist >= 1. */ /* Ensure newCurrent - maxDist >= ZSTD_WINDOW_START_INDEX. */
U32 const currentCycle1 = currentCycle0 == 0 ? cycleSize : currentCycle0; U32 const currentCycleCorrection = currentCycle < ZSTD_WINDOW_START_INDEX
U32 const newCurrent = currentCycle1 + MAX(maxDist, cycleSize); ? MAX(cycleSize, ZSTD_WINDOW_START_INDEX)
: 0;
U32 const newCurrent = currentCycle
+ currentCycleCorrection
+ MAX(maxDist, cycleSize);
U32 const correction = curr - newCurrent; U32 const correction = curr - newCurrent;
/* maxDist must be a power of two so that: /* maxDist must be a power of two so that:
* (newCurrent & cycleMask) == (curr & cycleMask) * (newCurrent & cycleMask) == (curr & cycleMask)
@ -1076,14 +1082,20 @@ MEM_STATIC U32 ZSTD_window_correctOverflow(ZSTD_window_t* window, U32 cycleLog,
window->base += correction; window->base += correction;
window->dictBase += correction; window->dictBase += correction;
if (window->lowLimit <= correction) window->lowLimit = 1; if (window->lowLimit < correction + ZSTD_WINDOW_START_INDEX) {
else window->lowLimit -= correction; window->lowLimit = ZSTD_WINDOW_START_INDEX;
if (window->dictLimit <= correction) window->dictLimit = 1; } else {
else window->dictLimit -= correction; window->lowLimit -= correction;
}
if (window->dictLimit < correction + ZSTD_WINDOW_START_INDEX) {
window->dictLimit = ZSTD_WINDOW_START_INDEX;
} else {
window->dictLimit -= correction;
}
/* Ensure we can still reference the full window. */ /* Ensure we can still reference the full window. */
assert(newCurrent >= maxDist); assert(newCurrent >= maxDist);
assert(newCurrent - maxDist >= 1); assert(newCurrent - maxDist >= ZSTD_WINDOW_START_INDEX);
/* Ensure that lowLimit and dictLimit didn't underflow. */ /* Ensure that lowLimit and dictLimit didn't underflow. */
assert(window->lowLimit <= newCurrent); assert(window->lowLimit <= newCurrent);
assert(window->dictLimit <= newCurrent); assert(window->dictLimit <= newCurrent);