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Fix #15006: FP invalidFree with new array #8880

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Fix #15006: FP invalidFree with new array #8880

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c3b8295
test
ludviggunne Sep 21, 2026
061ab75
fix
ludviggunne Sep 21, 2026
f25e935
new test
ludviggunne Oct 1, 2026
7ae750b
update
ludviggunne Oct 1, 2026
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9 changes: 9 additions & 0 deletions lib/checkother.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -2850,6 +2850,15 @@ void CheckOtherImpl::checkInvalidFree()

const int varIndex = tok->strAt(1) == "(" ? 2 :
tok->strAt(3) == "(" ? 4 : 1;
const Token *op = tok->tokAt(varIndex + 1);
if (std::any_of(op->values().cbegin(),
op->values().cend(),
[&](const ValueFlow::Value &value) {
if (!value.isSymbolicValue() || !value.isKnown() || value.intvalue != 0 || !value.tokvalue)
return false;
return value.tokvalue->str() == "new";

@danmar danmar Oct 1, 2026

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This is an AI review take it with a grain of salt. Please feel free to reject it by clicking on Resolve

The new version fixes the char *q = p - 1; false negative, thanks. But since only new is accepted now, the same false positive is still there for malloc()/free():

void f(void) {
    char *p = malloc(10);
    ++p;
    free(p - 1);   // invalidFree, same as on main
}

Accepting allocation functions here (Token::simpleMatch(value.tokvalue, "(") && mSettings.library.getAllocFuncInfo(value.tokvalue->previous())) is not enough on its own. I tried it, and p - 1 gets no symbolic value at all for malloc, only possible 0 from the failed-allocation path. So this probably needs more valueflow work. If that is out of scope here, maybe add the malloc case as a TODO_ASSERT_EQUALS test, or open a follow-up ticket, so it isn't forgotten.

}))
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const int var1 = tok->tokAt(varIndex)->varId();
const int var2 = tok->tokAt(varIndex + 2)->varId();
const auto alloc1 = utils::as_const(inconclusive).find(var1);
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14 changes: 14 additions & 0 deletions lib/valueflow.cpp
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Expand Up @@ -3737,6 +3737,20 @@ static void valueFlowSymbolicOperators(const SymbolDatabase& symboldatabase, con
continue;
if (Token::Match(tok, "<<|>>|/|-") && !astIsLHS(vartok))
continue;
if (Token::Match(tok, "+|-") && constant->intvalue != 0) {
std::unordered_set<nonneg int> ids;
for (const auto &value : vartok->values()) {
if (!value.isSymbolicValue())
continue;
if (!value.tokvalue)
continue;
if (!ids.insert(value.tokvalue->exprId()).second)
continue;
ValueFlow::Value newValue(value);
newValue.intvalue += tok->str() == "-" ? -constant->intvalue : constant->intvalue;
setTokenValue(tok, std::move(newValue), settings);
}
}
if (Token::Match(tok, "<<|>>|^|+|-|%or%") && constant->intvalue != 0)
continue;
if (Token::Match(tok, "*|/") && constant->intvalue != 1)
Expand Down
26 changes: 26 additions & 0 deletions test/testother.cpp
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Expand Up @@ -10070,6 +10070,32 @@ class TestOther : public TestFixture {
ASSERT_EQUALS(
"[test.cpp:2:9]: (style) Variable 'ptr' can be declared as pointer to const [constVariablePointer]\n",
errout_str());

check("void f() {\n"
" char *p = new char[1];\n"
" ++p;\n"
" delete [] (p - 1);\n"
"}\n");
ASSERT_EQUALS("[test.cpp:2:11]: (style) Variable 'p' can be declared as pointer to const [constVariablePointer]\n",
errout_str());

check("void f() {\n"
" char *p = new char[1];\n"
" delete [] (p - 1);\n"
"}\n");
ASSERT_EQUALS("[test.cpp:2:11]: (style) Variable 'p' can be declared as pointer to const [constVariablePointer]\n"
"[test.cpp:3:5]: (error) Mismatching address is deleted. The address you get from new must be deleted without offset. [invalidFree]\n"
, errout_str());

check("void f() {\n"
" char *p = new char[2];\n"
" char *q = p - 1;\n"
" delete [] (p - 1);\n"
" (void)q;\n"
"}\n");
ASSERT_EQUALS("[test.cpp:2:11]: (style) Variable 'p' can be declared as pointer to const [constVariablePointer]\n"
"[test.cpp:4:5]: (error) Mismatching address is deleted. The address you get from new must be deleted without offset. [invalidFree]\n",
errout_str());
}

void checkRedundantCopy() {
Expand Down
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