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Fix out-of-bounds read in FASTCOVER on small training samples - #4710
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eyupcanakman wants to merge 2 commits into
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When every training sample is smaller than the dmer size, splitPoint < 1 can shrink the training set below MAX(d, 8) after the total samples size check passes, so nbDmers underflows and FASTCOVER reads past the sample buffer (meta#4499). It now returns srcSize_wrong. Adds a unit test in basicUnitTests. The same underflow in COVER_ctx_init is addressed separately in meta#4690.
kevinjzhang
approved these changes
Nov 5, 2026
kevinjzhang
reviewed
Nov 5, 2026
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| /* Check the training set can hold at least one dmer, otherwise nbDmers underflows below */ | ||
| if (trainingSamplesSize < MAX(d, sizeof(U64))) { |
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MAX(d, sizeof(U64) is now referenced multiple times - it deserves to be a named quanity now. readLength would be good here.
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Done in 233eb64, all three uses go through readLength now.
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When every training sample is smaller than the dmer size,
FASTCOVER_ctx_initderivesnbDmersfrom the training set, whichsplitPoint < 1can shrink belowMAX(d, 8)even after the total samples size check passes. The subtraction underflows and the builder reads past the sample buffer (#4499).It now returns
srcSize_wrongfor a training set that small, the way the other invalid inputs already do. Adds a unit test inbasicUnitTests.COVER_ctx_inithas the same underflow, addressed separately in #4690.