check signed overflow in MSBuild arithmetic intrinsics

Author: Nussu06

lib/importproject.cpp

@@ -27,6 +27,7 @@
 
 #include <algorithm>
 #include <cctype>
+#include <climits>
 #include <cmath>
 #include <cstdlib>
 #include <cstring>
@@ -848,6 +849,44 @@ static std::string safeFormat(const char *fmt, Args... args) {
 #pragma clang diagnostic pop
 #endif
 
+// Checked signed arithmetic for the [MSBuild]::Add/Subtract/Multiply intrinsics.
+// Operands come straight from the (untrusted) project file, so the result can
+// exceed long long and the plain a+b / a-b / a*b would be signed-overflow UB.
+// These return false on overflow so the caller can report it instead.
+static bool addChecked(long long a, long long b, long long &res) {
+    if ((b > 0 && a > LLONG_MAX - b) || (b < 0 && a < LLONG_MIN - b))
+        return false;
+    res = a + b;
+    return true;
+}
+
+static bool subChecked(long long a, long long b, long long &res) {
+    if ((b < 0 && a > LLONG_MAX + b) || (b > 0 && a < LLONG_MIN + b))
+        return false;
+    res = a - b;
+    return true;
+}
+
+static bool mulChecked(long long a, long long b, long long &res) {
+    if (a > 0) {
+        if (b > 0) {
+            if (a > LLONG_MAX / b)
+                return false;
+        } else if (b < LLONG_MIN / a) {
+            return false;
+        }
+    } else {
+        if (b > 0) {
+            if (a < LLONG_MIN / b)
+                return false;
+        } else if (a != 0 && b < LLONG_MAX / a) {
+            return false;
+        }
+    }
+    res = a * b;
+    return true;
+}
+
 // Evaluate a $([ClassName]::Method(args)) static property function.
 // Returns an empty string for unknown or unimplementable functions rather
 // than throwing, so import can continue gracefully.
@@ -893,24 +932,46 @@ std::string ImportProject::applyMSBuildStaticFunction(const std::string &classNa
         if (args.size() == 2) {
             long long a = 0, b = 0;
             if (toInt(args[0], a) && toInt(args[1], b)) {
-                if (caseInsensitiveStringCompare(member, "Add") == 0)
-                    return std::to_string(a + b);
-                if (caseInsensitiveStringCompare(member, "Subtract") == 0)
-                    return std::to_string(a - b);
-                if (caseInsensitiveStringCompare(member, "Multiply") == 0)
-                    return std::to_string(a * b);
+                long long r = 0;
+                if (caseInsensitiveStringCompare(member, "Add") == 0) {
+                    if (!addChecked(a, b, r)) {
+                        addDebug("MSBuild::Add: integer overflow");
+                        return std::string();
+                    }
+                    return std::to_string(r);
+                }
+                if (caseInsensitiveStringCompare(member, "Subtract") == 0) {
+                    if (!subChecked(a, b, r)) {
+                        addDebug("MSBuild::Subtract: integer overflow");
+                        return std::string();
+                    }
+                    return std::to_string(r);
+                }
+                if (caseInsensitiveStringCompare(member, "Multiply") == 0) {
+                    if (!mulChecked(a, b, r)) {
+                        addDebug("MSBuild::Multiply: integer overflow");
+                        return std::string();
+                    }
+                    return std::to_string(r);
+                }
                 if (caseInsensitiveStringCompare(member, "Divide") == 0) {
                     if (b == 0) {
                         addDebug("MSBuild::Divide: division by zero");
                         return std::string();
                     }
+                    if (a == LLONG_MIN && b == -1) {
+                        addDebug("MSBuild::Divide: integer overflow");
+                        return std::string();
+                    }
                     return std::to_string(a / b);
                 }
                 if (caseInsensitiveStringCompare(member, "Modulo") == 0) {
                     if (b == 0) {
                         addDebug("MSBuild::Modulo: division by zero");
                         return std::string();
                     }
+                    if (a == LLONG_MIN && b == -1)
+                        return std::string("0");
                     return std::to_string(a % b);
                 }
             }

test/testimportproject.cpp

@@ -1211,6 +1211,14 @@ class TestImportProject : public TestFixture {
         ASSERT_EQUALS("3", cppcheck::testing::expandMSBuildExpression("$([MSBuild]::Divide(9, 3))"));
         ASSERT_EQUALS("2", cppcheck::testing::expandMSBuildExpression("$([MSBuild]::Modulo(5, 3))"));
 
+        // Operands that would overflow long long must not compute a signed-overflow
+        // (undefined-behavior) result; the operation yields the empty string instead.
+        ASSERT_EQUALS("", cppcheck::testing::expandMSBuildExpression("$([MSBuild]::Add(9223372036854775807, 1))"));
+        ASSERT_EQUALS("", cppcheck::testing::expandMSBuildExpression("$([MSBuild]::Subtract(-9223372036854775808, 1))"));
+        ASSERT_EQUALS("", cppcheck::testing::expandMSBuildExpression("$([MSBuild]::Multiply(9999999999, 9999999999))"));
+        ASSERT_EQUALS("", cppcheck::testing::expandMSBuildExpression("$([MSBuild]::Divide(-9223372036854775808, -1))"));
+        ASSERT_EQUALS("0", cppcheck::testing::expandMSBuildExpression("$([MSBuild]::Modulo(-9223372036854775808, -1))"));
+
         // --- $([MSBuild]::...) path helpers ---
         ASSERT_EQUALS("foo/", cppcheck::testing::expandMSBuildExpression("$([MSBuild]::EnsureTrailingSlash('foo'))"));
         ASSERT_EQUALS("foo/", cppcheck::testing::expandMSBuildExpression("$([MSBuild]::EnsureTrailingSlash('foo/'))"));