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Fixed #4510 (False positive: "Possible null pointer dereference if the default parameter value is used" after init)

This commit is contained in:
Zachary Blair 2013-04-25 00:25:56 -07:00
parent c3d1274db3
commit 35668380cf
3 changed files with 112 additions and 11 deletions
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64
lib/checknullpointer.cpp
View File

@ -1194,6 +1194,26 @@ void CheckNullPointer::nullConstantDereference()
}
}
/**
* @brief If tok is a function call that passes in a pointer such that
* the pointer may be modified, this function will remove that
* pointer from pointerArgs.
*/
void CheckNullPointer::removeAssignedVarFromSet(const Token* tok, std::set<unsigned int>& pointerArgs)
{
// Common functions that are known NOT to modify their pointer argument
const char safeFunctions[] = "printf|sprintf|fprintf|vprintf";
// If a pointer's address is passed into a function, stop considering it
if (Token::Match(tok->previous(), "[;{}] %var% (")) {
const Token* endParen = tok->next()->link();
for (const Token* tok2 = tok->next(); tok2 != endParen; tok2 = tok2->next()) {
if (tok2->isName() && tok2->varId() > 0 && !Token::Match(tok, safeFunctions)) {
pointerArgs.erase(tok2->varId());
}
}
}
}
/**
* @brief Does one part of the check for nullPointer().
@ -1223,8 +1243,8 @@ void CheckNullPointer::nullPointerDefaultArgument()
// Report an error if any of the default-NULL arguments are dereferenced
if (!pointerArgs.empty()) {
bool unknown = _settings->inconclusive;
for (const Token *tok = scope->classStart; tok != scope->classEnd; tok = tok->next()) {
// If we encounter a possible NULL-pointer check, skip over its body
if (Token::simpleMatch(tok, "if ( ")) {
bool dependsOnPointer = false;
@ -1241,31 +1261,53 @@ void CheckNullPointer::nullPointerDefaultArgument()
// pointer check for the pointers referenced in its condition
const Token *endOfIf = startOfIfBlock->link();
bool isExitOrReturn =
Token::findmatch(startOfIfBlock, "exit|return", endOfIf) != NULL;
Token::findmatch(startOfIfBlock, "exit|return|throw", endOfIf) != NULL;
for (const Token *tok2 = tok->next(); tok2 != endOfCondition; tok2 = tok2->next()) {
if (tok2->isName() && tok2->varId() > 0 &&
pointerArgs.count(tok2->varId()) > 0) {
// If the if() depends on a pointer and may return, stop
// considering that pointer because it may be a NULL-pointer
// check that returns if the pointer is NULL.
if (Token::Match(tok, "if ( %var% == 0 )")) {
const unsigned int var = tok->tokAt(2)->varId();
if (var > 0 && pointerArgs.count(var) > 0) {
if (isExitOrReturn)
pointerArgs.erase(tok2->varId());
pointerArgs.erase(var);
else
dependsOnPointer = true;
}
} else {
for (const Token *tok2 = tok->next(); tok2 != endOfCondition; tok2 = tok2->next()) {
if (tok2->isName() && tok2->varId() > 0 &&
pointerArgs.count(tok2->varId()) > 0) {
// If the if() depends on a pointer and may return, stop
// considering that pointer because it may be a NULL-pointer
// check that returns if the pointer is NULL.
if (isExitOrReturn)
pointerArgs.erase(tok2->varId());
else
dependsOnPointer = true;
}
}
}
if (dependsOnPointer && endOfIf) {
for (; tok != endOfIf; tok = tok->next()) {
// If a pointer is assigned a new value, stop considering it.
if (Token::Match(tok, "%var% ="))
pointerArgs.erase(tok->varId());
else
removeAssignedVarFromSet(tok, pointerArgs);
}
continue;
}
}
// If there is a noreturn function (e.g. exit()), stop considering the rest of
// this function.
bool unknown = false;
if (Token::Match(tok, "return|throw|exit") ||
(_tokenizer->IsScopeNoReturn(tok, &unknown) && !unknown))
break;
removeAssignedVarFromSet(tok, pointerArgs);
if (tok->varId() == 0 || pointerArgs.count(tok->varId()) == 0)
continue;
@ -1276,7 +1318,7 @@ void CheckNullPointer::nullPointerDefaultArgument()
// If a pointer dereference is preceded by an && or ||,
// they serve as a sequence point so the dereference
// may not be executed.
if (isPointerDeRef(tok, unknown) &&
if (isPointerDeRef(tok, unknown) && !unknown &&
tok->strAt(-1) != "&&" && tok->strAt(-1) != "||" &&
tok->strAt(-2) != "&&" && tok->strAt(-2) != "||")
nullPointerDefaultArgError(tok, tok->str());

5
lib/checknullpointer.h
View File

@ -152,6 +152,11 @@ private:
*/
void nullPointerDefaultArgument();
/**
* @brief Removes any variable that may be assigned from pointerArgs.
*/
void removeAssignedVarFromSet(const Token* tok, std::set<unsigned int>& pointerArgs);
/**
* @brief Investigate if function call can make pointer null. If
* the pointer is passed by value it can't be made a null pointer.

54
test/testnullpointer.cpp
View File

@ -2110,6 +2110,13 @@ private:
"}");
ASSERT_EQUALS("[test.cpp:2]: (warning) Possible null pointer dereference if the default parameter value is used: p\n", errout.str());
check("void f(int *p = 0) {\n"
" if (!p)\n"
" return;\n"
" *p = 0;\n"
"}");
ASSERT_EQUALS("", errout.str());
check("void f(char a, int *p = 0) {\n"
" *p = 0;\n"
"}");
@ -2195,6 +2202,53 @@ private:
" return !p || *p;\n"
"}");
ASSERT_EQUALS("", errout.str());
// bar may initialize p but be can't know for sure without knowing
// if p is passed in by reference and is modified by bar()
check("void f(int *p = 0) {\n"
" bar(p);\n"
" *p = 0;\n"
"}");
ASSERT_EQUALS("", errout.str());
check("void f(int *p = 0) {\n"
" printf(\"%d\", p);\n"
" *p = 0;\n"
"}");
ASSERT_EQUALS("[test.cpp:3]: (warning) Possible null pointer dereference if the default parameter value is used: p\n", errout.str());
// The init() function may or may not initialize p, but since the address
// of p is passed in, it's a good bet that p may be modified and
// so we should not report an error.
check("void f(int *p = 0) {\n"
" init(&p);\n"
" *p = 0;\n"
"}");
ASSERT_EQUALS("", errout.str());
check("void init(int* &g);\n"
"void f(int *p = 0) {\n"
" init(p);\n"
" *p = 0;\n"
"}");
ASSERT_EQUALS("", errout.str());
check("void f(int *p = 0) {\n"
" if (p == 0) {\n"
" init(&p);\n"
" }\n"
" *p = 0;\n"
"}");
ASSERT_EQUALS("", errout.str());
check("void f(int *p = 0) {\n"
" if (p == 0) {\n"
" throw SomeException;\n"
" }\n"
" *p = 0;\n"
"}");
ASSERT_EQUALS("", errout.str());
}