'rtbTable' may be underflowed because 'proba' is used without checking for a non-negative as index of rtbTable[].

Add check: proba >= 0

Cc: stable@vger.kernel.org # v5.10+ Fixes: e0c1b49f5b67 ("lib: zstd: Upgrade to latest upstream zstd version 1.4.10") Signed-off-by: Ilya Krutskih devsec@tpz.ru --- lib/zstd/compress/fse_compress.c | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/lib/zstd/compress/fse_compress.c b/lib/zstd/compress/fse_compress.c index 44a3c10becf2..6b83f8bc943a 100644 --- a/lib/zstd/compress/fse_compress.c +++ b/lib/zstd/compress/fse_compress.c @@ -492,9 +492,10 @@ size_t FSE_normalizeCount (short* normalizedCounter, unsigned tableLog, stillToDistribute--; } else { short proba = (short)((count[s]*step) >> scale); - if (proba<8) { - U64 restToBeat = vStep * rtbTable[proba]; - proba += (count[s]*step) - ((U64)proba<<scale) > restToBeat; + if ((proba >= 0) && (proba < 8)) { + U64 restToBeat = vStep * rtbTable[proba]; + + proba += (count[s]*step) - ((U64)proba<<scale) > restToBeat; } if (proba > largestP) { largestP=proba; largest=s; } normalizedCounter[s] = proba;