From 4dc406e8cac9d95817d1ac5ebc89665cafa2120b Mon Sep 17 00:00:00 2001 From: Florin Malita Date: Tue, 15 May 2018 22:48:07 -0400 Subject: [PATCH 9/9] Prevent int underflow when parsing exponents When parsing negative exponents, the current implementation takes precautions for |exp| to not underflow int. But that is not sufficient: later on [1], |exp + expFrac| is also stored to an int - so we must ensure that the sum stays within int representable values. Update the exp clamping logic to take expFrac into account. [1] https://github.com/Tencent/rapidjson/blob/master/include/rapidjson/reader.h#L1690 --- include/rapidjson/reader.h | 11 ++++++++++- test/unittest/readertest.cpp | 1 + 2 files changed, 11 insertions(+), 1 deletion(-) diff --git a/include/rapidjson/reader.h b/include/rapidjson/reader.h index 19f8849b..a9f50230 100644 --- a/include/rapidjson/reader.h +++ b/include/rapidjson/reader.h @@ -1302,9 +1302,18 @@ private: if (RAPIDJSON_LIKELY(s.Peek() >= '0' && s.Peek() <= '9')) { exp = static_cast(s.Take() - '0'); if (expMinus) { + // (exp + expFrac) must not underflow int => we're detecting when -exp gets + // dangerously close to INT_MIN (a pessimistic next digit 9 would push it into + // underflow territory): + // + // -(exp * 10 + 9) + expFrac >= INT_MIN + // <=> exp <= (expFrac - INT_MIN - 9) / 10 + RAPIDJSON_ASSERT(expFrac <= 0); + int maxExp = (expFrac + 2147483639) / 10; + while (RAPIDJSON_LIKELY(s.Peek() >= '0' && s.Peek() <= '9')) { exp = exp * 10 + static_cast(s.Take() - '0'); - if (exp >= 214748364) { // Issue #313: prevent overflow exponent + if (RAPIDJSON_UNLIKELY(exp > maxExp)) { while (RAPIDJSON_UNLIKELY(s.Peek() >= '0' && s.Peek() <= '9')) // Consume the rest of exponent s.Take(); } diff --git a/test/unittest/readertest.cpp b/test/unittest/readertest.cpp index 64a1f9c3..65163de6 100644 --- a/test/unittest/readertest.cpp +++ b/test/unittest/readertest.cpp @@ -242,6 +242,7 @@ static void TestParseDouble() { TEST_DOUBLE(fullPrecision, "1e-214748363", 0.0); // Maximum supported negative exponent TEST_DOUBLE(fullPrecision, "1e-214748364", 0.0); TEST_DOUBLE(fullPrecision, "1e-21474836311", 0.0); + TEST_DOUBLE(fullPrecision, "1.00000000001e-2147483638", 0.0); TEST_DOUBLE(fullPrecision, "0.017976931348623157e+310", 1.7976931348623157e+308); // Max double in another form // Since -- 2.45.2