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Bugfix: Small buffer size causes buffer overrun when invoking String::Ctor with large float/double value. #131

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merged 3 commits into from
Dec 10, 2020
Merged

Bugfix: Small buffer size causes buffer overrun when invoking String::Ctor with large float/double value. #131

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f3cfa2f
Calling String::String(float ...) with +/- FLT_MAX or String::String(…
aentinger Dec 9, 2020
952d776
Increase buffer size in order to avoid buffer overflow when using lar…
aentinger Dec 9, 2020
3c76ef2
Ensure that no buffer overflow can occur by limiting the number of po…
aentinger Dec 9, 2020
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22 changes: 18 additions & 4 deletions api/String.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -20,14 +20,24 @@
*/

#include "String.h"
#include "Common.h"
#include "itoa.h"
#include "deprecated-avr-comp/avr/dtostrf.h"

#include <float.h>

namespace arduino {

/*********************************************/
/* Constructors */
/* Static Member Initialisation */
/*********************************************/

namespace arduino {
size_t const String::FLT_MAX_DECIMAL_PLACES;
size_t const String::DBL_MAX_DECIMAL_PLACES;

/*********************************************/
/* Constructors */
/*********************************************/

String::String(const char *cstr)
{
Expand Down Expand Up @@ -111,15 +121,19 @@ String::String(unsigned long value, unsigned char base)

String::String(float value, unsigned char decimalPlaces)
{
static size_t const FLOAT_BUF_SIZE = FLT_MAX_10_EXP + FLT_MAX_DECIMAL_PLACES + 1 /* '-' */ + 1 /* '.' */ + 1 /* '\0' */;
init();
char buf[33];
char buf[FLOAT_BUF_SIZE];
decimalPlaces = min(decimalPlaces, FLT_MAX_DECIMAL_PLACES);
*this = dtostrf(value, (decimalPlaces + 2), decimalPlaces, buf);
}

String::String(double value, unsigned char decimalPlaces)
{
static size_t const DOUBLE_BUF_SIZE = DBL_MAX_10_EXP + DBL_MAX_DECIMAL_PLACES + 1 /* '-' */ + 1 /* '.' */ + 1 /* '\0' */;
init();
char buf[33];
char buf[DOUBLE_BUF_SIZE];
decimalPlaces = min(decimalPlaces, DBL_MAX_DECIMAL_PLACES);
*this = dtostrf(value, (decimalPlaces + 2), decimalPlaces, buf);
}

Expand Down
3 changes: 3 additions & 0 deletions api/String.h
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Expand Up @@ -58,6 +58,9 @@ class String
typedef void (String::*StringIfHelperType)() const;
void StringIfHelper() const {}

static size_t const FLT_MAX_DECIMAL_PLACES = 10;
static size_t const DBL_MAX_DECIMAL_PLACES = FLT_MAX_DECIMAL_PLACES;

public:
// constructors
// creates a copy of the initial value.
Expand Down
40 changes: 33 additions & 7 deletions test/src/String/test_String.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -6,6 +6,8 @@
* INCLUDE
**************************************************************************************/

#include <float.h>

#include <catch.hpp>

#include <String.h>
Expand Down Expand Up @@ -80,16 +82,40 @@ TEST_CASE ("Testing String(unsigned long, unsigned char base = 10) constructor()

TEST_CASE ("Testing String(float, unsigned char decimalPlaces = 2) constructor()", "[String-Ctor-10]")
{
float const val = 1.234f;
arduino::String str(val);
REQUIRE(strcmp(str.c_str(), "1.23") == 0);
WHEN ("String::String (some float value)")
{
arduino::String str(1.234f);
REQUIRE(strcmp(str.c_str(), "1.23") == 0);
}
WHEN ("String::String (FLT_MAX)")
{
arduino::String str(FLT_MAX);
REQUIRE(strcmp(str.c_str(), "340282346638528859811704183484516925440.00") == 0);
}
WHEN ("String::String (-FLT_MAX)")
{
arduino::String str(-FLT_MAX);
REQUIRE(strcmp(str.c_str(), "-340282346638528859811704183484516925440.00") == 0);
}
}

TEST_CASE ("Testing String(double, unsigned char decimalPlaces = 2) constructor()", "[String-Ctor-11]")
{
double const val = 5.678;
arduino::String str(val);
REQUIRE(strcmp(str.c_str(), "5.68") == 0);
WHEN ("String::String (some double value)")
{
arduino::String str(5.678);
REQUIRE(strcmp(str.c_str(), "5.68") == 0);
}
WHEN ("String::String (DBL_MAX)")
{
arduino::String str(DBL_MAX);
REQUIRE(strcmp(str.c_str(), "179769313486231570814527423731704356798070567525844996598917476803157260780028538760589558632766878171540458953514382464234321326889464182768467546703537516986049910576551282076245490090389328944075868508455133942304583236903222948165808559332123348274797826204144723168738177180919299881250404026184124858368.00") == 0);
}
WHEN ("String::String (-DBL_MAX)")
{
arduino::String str(-DBL_MAX);
REQUIRE(strcmp(str.c_str(), "-179769313486231570814527423731704356798070567525844996598917476803157260780028538760589558632766878171540458953514382464234321326889464182768467546703537516986049910576551282076245490090389328944075868508455133942304583236903222948165808559332123348274797826204144723168738177180919299881250404026184124858368.00") == 0);
}
}

TEST_CASE ("Testing String(const __FlashStringHelper) constructor() with invalid buffer", "[String-Ctor-12]")
Expand Down Expand Up @@ -131,4 +157,4 @@ TEST_CASE ("Testing String(String &&) with move(String &rhs) from larger to smal
arduino::String str1("Arduino");
str = static_cast<arduino::String&&>(str1);
REQUIRE(str1.compareTo("Arduino") == 0);
}
}