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Add more safety checks to variadic function calls in checked scope #1182

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Sep 10, 2021
Merged

Add more safety checks to variadic function calls in checked scope #1182

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b1a176f
Add more safety checks to variadic functions calls in checked scope
Sep 9, 2021
5fd3ed0
Added a couple of comments
Sep 9, 2021
7faaadf
Merge branch 'master' into varargs3
Sep 9, 2021
1d7515b
Add issue
Sep 9, 2021
55b89e3
Update clang/lib/Sema/SemaChecking.cpp
Sep 9, 2021
f71b669
Fix windows test
Sep 9, 2021
a579903
f
Sep 9, 2021
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3 changes: 3 additions & 0 deletions clang/include/clang/Basic/DiagnosticSemaKinds.td
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Original file line number Diff line number Diff line change
Expand Up @@ -11530,6 +11530,9 @@ def err_bounds_type_annotation_lost_checking : Error<
def err_checked_scope_scanf_width : Error<
"in a checked scope width is not allowed with format specifier in scanf">;

def err_checked_scope_disallowed_format_specifier : Error<
"in a checked scope %0 format specifier is not allowed %1">;

def err_pragma_pop_checked_scope_mismatch : Error<
"#pragma CHECKED_SCOPE pop with no matching #pragma CHECKED_SCOPE push">;

Expand Down
85 changes: 71 additions & 14 deletions clang/lib/Sema/SemaChecking.cpp
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Expand Up @@ -7581,10 +7581,13 @@ class CheckFormatHandler : public analyze_format_string::FormatStringHandler {

void HandleNullChar(const char *nullCharacter) override;

// Note: IsFuncScanfLike = true means that the variadic function being called
// is scanf-like. IsFuncScanfLike = false means that the function is
// printf-like.
void CheckVarargsInCheckedScope(
const analyze_format_string::ConversionSpecifier &CS,
const char *StartSpecifier, unsigned SpecifierLen, const Expr *E,
SmallString<128> FSString);
SmallString<128> FSString, bool IsFuncScanfLike = false);

template <typename Range>
static void
Expand Down Expand Up @@ -7945,7 +7948,7 @@ CheckFormatHandler::CheckNumArgs(
void CheckFormatHandler::CheckVarargsInCheckedScope(
const analyze_format_string::ConversionSpecifier &CS,
const char *StartSpecifier, unsigned SpecifierLen, const Expr *E,
SmallString<128> FSString) {
SmallString<128> FSString, bool IsFuncScanfLike) {

// Check arguments to variadic functions like printf/scanf, etc in checked
// scope. This function is called per argument. E is current argument that
Expand All @@ -7958,34 +7961,87 @@ void CheckFormatHandler::CheckVarargsInCheckedScope(
return;

QualType ArgTy = E->getType();
bool EmitVariadicFuncDiag = false;
std::string ExpectedTyMsg;

switch (CS.getKind()) {
default:
// In scanf-like functions, only allow _Ptr type arguments.
if (IsFuncScanfLike) {
if (ArgTy->isCheckedPointerNtArrayType() ||
ArgTy->isNtCheckedArrayType() ||
ArgTy->isCheckedPointerArrayType() ||
ArgTy->isCheckedArrayType()) {
EmitFormatDiagnostic(
S.PDiag(diag::err_checked_scope_invalid_format_specifier_argument)
<< FSString << "_Ptr",
E->getExprLoc(), /*IsStringLocation*/false,
getSpecifierRange(StartSpecifier, SpecifierLen));
}

// In printf-like functions, only allow scalar type arguments with format
// specifiers other than %s.

// TODO: Currently, we do not handle the case where an out-of-bounds
// null-terminated array is passed as an argument to %s. The following code
// is allowed even though it might be a safety hole.
// _Checked {
// _Nt_array_ptr<char> p : count(5);
// printf("%s", p + 1234);
// }
// Issue https://github.com/microsoft/checkedc-clang/issues/1178 tracks this.

} else {
if (ArgTy->isCheckedPointerType()) {
EmitFormatDiagnostic(
S.PDiag(diag::err_checked_scope_invalid_format_specifier_argument)
<< FSString << "scalar",
E->getExprLoc(), /*IsStringLocation*/false,
getSpecifierRange(StartSpecifier, SpecifierLen));
}
}
break;

// Check if the argument corresponding to the %s format specifier is either
// _Nt_array_ptr or _Nt_checked.
case ConversionSpecifier::sArg:
if (!ArgTy->isCheckedPointerNtArrayType() &&
!ArgTy->isNtCheckedArrayType()) {
EmitVariadicFuncDiag = true;
ExpectedTyMsg = "null-terminated";
if (IsFuncScanfLike) {
EmitFormatDiagnostic(
S.PDiag(diag::err_checked_scope_disallowed_format_specifier)
<< FSString << "in scanf",
E->getExprLoc(), /*IsStringLocation*/false,
getSpecifierRange(StartSpecifier, SpecifierLen));

} else if (!ArgTy->isCheckedPointerNtArrayType() &&
!ArgTy->isNtCheckedArrayType()) {
EmitFormatDiagnostic(
S.PDiag(diag::err_checked_scope_invalid_format_specifier_argument)
<< FSString << "null-terminated",
E->getExprLoc(), /*IsStringLocation*/false,
getSpecifierRange(StartSpecifier, SpecifierLen));
}
break;
}

if (EmitVariadicFuncDiag) {
// Disallow %p format specifier with scanf-like functions.
case ConversionSpecifier::pArg:
if (IsFuncScanfLike) {
EmitFormatDiagnostic(
S.PDiag(diag::err_checked_scope_disallowed_format_specifier)
<< FSString << "with scanf",
E->getExprLoc(), /*IsStringLocation*/false,
getSpecifierRange(StartSpecifier, SpecifierLen));
}
break;

// Disallow %n specifier in checked scope.
case ConversionSpecifier::nArg:
EmitFormatDiagnostic(
S.PDiag(diag::err_checked_scope_invalid_format_specifier_argument)
<< FSString << ExpectedTyMsg,
S.PDiag(diag::err_checked_scope_disallowed_format_specifier)
<< FSString << "",
E->getExprLoc(), /*IsStringLocation*/false,
getSpecifierRange(StartSpecifier, SpecifierLen));
break;
}
}


template<typename Range>
void CheckFormatHandler::EmitFormatDiagnostic(PartialDiagnostic PDiag,
SourceLocation Loc,
Expand Down Expand Up @@ -9176,7 +9232,8 @@ bool CheckScanfHandler::HandleScanfSpecifier(
SmallString<128> FSString;
llvm::raw_svector_ostream os(FSString);
FS.toString(os);
CheckVarargsInCheckedScope(CS, startSpecifier, specifierLen, Ex, FSString);
CheckVarargsInCheckedScope(CS, startSpecifier, specifierLen, Ex, FSString,
/*IsFuncScanfLike*/ true);

analyze_format_string::ArgType::MatchKind Match =
AT.matchesType(S.Context, Ex->getType());
Expand Down
4 changes: 2 additions & 2 deletions clang/test/CheckedC/checked-scope/variadic-functions-win.c
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Original file line number Diff line number Diff line change
Expand Up @@ -19,8 +19,8 @@ int MyScanf(const char *format : itype(_Nt_array_ptr<const char>), ...)

void f1 (_Nt_array_ptr<char> p) {
_Checked {
printf("%Z", p); // expected-error {{'Z' conversion specifier is not supported by ISO C}}
MyPrintf("%Z", p); // expected-error {{'Z' conversion specifier is not supported by ISO C}}
printf("%Z", p); // expected-error {{'Z' conversion specifier is not supported by ISO C}} expected-error {{in a checked scope %Z format specifier requires scalar argument}}
MyPrintf("%Z", p); // expected-error {{'Z' conversion specifier is not supported by ISO C}} expected-error {{in a checked scope %Z format specifier requires scalar argument}}
scanf("%Z", p); // expected-error {{invalid conversion specifier 'Z'}}
MyScanf("%Z", p); // expected-error {{invalid conversion specifier 'Z'}}

Expand Down
105 changes: 92 additions & 13 deletions clang/test/CheckedC/checked-scope/variadic-functions.c
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Expand Up @@ -5,6 +5,25 @@
// variadic-functions-win.c and the non-windows tests are in
// variadic-functions-non-win.c.

// The checking of variadic functions in checked scope follows these rules:
// 1. All warnings issued by the -Wformat family of flags are errors in checked
// scope.
// 2. No bounds checking of arguments to variadic functions like printf/scanf,
// etc is done.

// For printf-like functions:
// 3. %s is allowed only with arg type _Nt_array_ptr or _Nt_checked.
// 4. %p is allowed with any arg type.
// 5. %n is disallowed.
// 6. For all other format specifiers, only scalar arg types are allowed.

// For scanf-like functions:
// 7. %s is disallowed.
// 8. All width modifiers to format specifiers are disallowed.
// 9. %p is disallowed
// 10. %n is disallowed
// 11. For all other format specifiers, only _Ptr arg types are allowed.

// RUN: %clang_cc1 -fcheckedc-extension -verify \
// RUN: -verify-ignore-unexpected=note %s

Expand Down Expand Up @@ -57,41 +76,96 @@ void f1(_Nt_array_ptr<char> chk, char *unchk1, _Array_ptr<char> arr) {
int a = 1, b = 2;
char *unchk2;

// Calling printf-scanf-like functions with unchecked pointers is allowed in
// unchecked scope.
printf("%d %s %d %s", 1, unchk1, 2, unchk2);
MyPrintf("%d %s %d %s", 1, unchk1, 2, unchk2);
scanf("%d %s %d %s", &a, unchk1, &b, unchk2);
MyScanf("%d %s %d %s", &a, unchk1, &b, unchk2);

_Checked {
// Calling printf-scanf-like functions with unchecked pointers is disallowed
// in checked scope.
printf("%d %s %d %s", 1, unchk1, 2, unchk2); // expected-error {{local variable used in a checked scope must have a checked type}} expected-error {{parameter used in a checked scope must have a checked type or a bounds-safe interface}}
MyPrintf("%d %s %d %s", 1, unchk1, 2, unchk2); // expected-error {{local variable used in a checked scope must have a checked type}} expected-error {{parameter used in a checked scope must have a checked type or a bounds-safe interface}}
scanf("%d %s %d %s", &a, unchk1, &b, unchk2); // expected-error {{local variable used in a checked scope must have a checked type}} expected-error {{parameter used in a checked scope must have a checked type or a bounds-safe interface}}
MyScanf("%d %s %d %s", &a, unchk1, &b, unchk2); // expected-error {{local variable used in a checked scope must have a checked type}} expected-error {{parameter used in a checked scope must have a checked type or a bounds-safe interface}}


// For printf-like functions %s is allowed only with arg type _Nt_array_ptr or _Nt_checked.
printf("%s", arr); // expected-error {{in a checked scope %s format specifier requires null-terminated argument}}
MyPrintf("%s", arr); // expected-error {{in a checked scope %s format specifier requires null-terminated argument}}
scanf("%s", arr); // expected-error {{in a checked scope %s format specifier requires null-terminated argument}}
MyScanf("%s", arr); // expected-error {{in a checked scope %s format specifier requires null-terminated argument}}

// For scanf-like functions %s is disallowed in checked scope.
scanf("%s", arr); // expected-error {{in a checked scope %s format specifier is not allowed in scanf}}
MyScanf("%s", arr); // expected-error {{in a checked scope %s format specifier is not allowed in scanf}}

_Nt_array_ptr<char> p = "a";

// For printf-like functions %s is allowed in checked scope.
printf("%10s", p);
MyPrintf("%10s", p);

// For scanf-like functions %s is disallowed in checked scope.
scanf("%10s", p); // expected-error {{in a checked scope %10s format specifier is not allowed in scanf}} expected-error {{in a checked scope width is not allowed with format specifier in scanf}}
MyScanf("%10s", p); // expected-error {{in a checked scope %10s format specifier is not allowed in scanf}} expected-error {{in a checked scope width is not allowed with format specifier in scanf}}

_Ptr<int> i = 0;
_Ptr<void> q = 0;

// For printf/scanf-like functions %n is disallowed in checked scope.
printf("hello\n%n", i); // expected-error {{in a checked scope %n format specifier is not allowed}}
MyPrintf("hello\n%n", i); // expected-error {{in a checked scope %n format specifier is not allowed}}
scanf("%n", i); // expected-error {{in a checked scope %n format specifier is not allowed}}
MyScanf("%n", i); // expected-error {{in a checked scope %n format specifier is not allowed}}

// For printf-like functions %p is allowed in checked scope.
printf("%p", q);
MyPrintf("%p", q);

// For scanf-like functions %p is disallowed in checked scope.
scanf("%p", &q); // expected-error {{in a checked scope %p format specifier is not allowed with scanf}}
MyScanf("%p", &q); // expected-error {{in a checked scope %p format specifier is not allowed with scanf}}

int arr _Checked[5];

// For printf-like functions for format specifiers other than %s, only scalar
// arg types are allowed in checked scope.
printf("%d", arr[4]);
printf("%d", *i);

printf("%d", arr); // expected-error {{format specifies type 'int' but the argument has type '_Array_ptr<int>'}} expected-error {{in a checked scope %d format specifier requires scalar argument}}
MyPrintf("%d", arr); // expected-error {{format specifies type 'int' but the argument has type '_Array_ptr<int>'}} expected-error {{in a checked scope %d format specifier requires scalar argument}}

// For scanf-like functions only _Ptr arg types are allowed in checked scope.
scanf("%d", arr); // expected-error {{in a checked scope %d format specifier requires _Ptr argument}}
MyScanf("%d", arr); // expected-error {{in a checked scope %d format specifier requires _Ptr argument}}
}
}

void f2 (_Nt_array_ptr<char> p, _Array_ptr<char> arr, _Ptr<FILE> fp) {
char *s;

// In checked scope, fprintf, sprintf, snprintf, fscanf, sscanf, etc follow
// rules similar to printf/scanf.

_Checked {
fprintf(fp, "%s", arr); // expected-error {{in a checked scope %s format specifier requires null-terminated argument}}
sprintf(s, "%s", arr); // expected-error {{local variable used in a checked scope must have a checked type}}
snprintf(p, 1, "%s", arr); // expected-error {{in a checked scope %s format specifier requires null-terminated argument}}

fscanf(fp, "%s", arr); // expected-error {{in a checked scope %s format specifier requires null-terminated argument}}
sscanf(p, "%s", arr); // expected-error {{in a checked scope %s format specifier requires null-terminated argument}}
fscanf(fp, "%s", arr); // expected-error {{in a checked scope %s format specifier is not allowed in scanf}}
sscanf(p, "%s", arr); // expected-error {{in a checked scope %s format specifier is not allowed in scanf}}
}
}

void f3(_Nt_array_ptr<char> p, _Array_ptr<char> arr, _Ptr<FILE> fp) {
va_list args;
char *s;

// In checked scope, vprintf, vscanf, etc follow rules similar to
// printf/scanf.

_Checked {
vprintf(p, args); // expected-error {{local variable used in a checked scope must have a checked type}}
vfprintf(fp, "%s", args); // expected-error {{local variable used in a checked scope must have a checked type}}
Expand All @@ -104,6 +178,9 @@ _Checked {
}

void f4 (_Nt_array_ptr<char> p, _Nt_array_ptr<wchar_t> w, _Ptr<int> ptr, _Ptr<void> voidPtr) {
// These diagnostics issued by the -Wformat family of flags are treated as
// errors in checked scope.

_Checked {
printf(p); // expected-error {{format string is not a string literal (potentially insecure)}}
MyPrintf(p); // expected-error {{format string is not a string literal (potentially insecure)}}
Expand Down Expand Up @@ -135,11 +212,6 @@ _Checked {
scanf("", p); // expected-error {{format string is empty}}
MyScanf("", p); // expected-error {{format string is empty}}

printf("%10s", p);
MyPrintf("%10s", p);
scanf("%10s", p); // expected-error {{in a checked scope width is not allowed with format specifier in scanf}}
MyScanf("%10s", p); // expected-error {{in a checked scope width is not allowed with format specifier in scanf}}

printf("%d", 1.0); // expected-error {{format specifies type 'int' but the argument has type 'double'}}
MyPrintf("%d", 1.0); // expected-error {{format specifies type 'int' but the argument has type 'double'}}
scanf("%d", 1.0); // expected-error {{format specifies type 'int *' but the argument has type 'double'}}
Expand Down Expand Up @@ -175,16 +247,21 @@ _Checked {
scanf("%P", p); // expected-error {{invalid conversion specifier 'P'}}
MyScanf("%P", p); // expected-error {{invalid conversion specifier 'P'}}

printf("%S", w); // expected-error {{'S' conversion specifier is not supported by ISO C}}
MyPrintf("%S", w); // expected-error {{'S' conversion specifier is not supported by ISO C}}
scanf("%S", w); // expected-error {{'S' conversion specifier is not supported by ISO C}}
MyScanf("%S", w); // expected-error {{'S' conversion specifier is not supported by ISO C}}
printf("%S", w); // expected-error {{'S' conversion specifier is not supported by ISO C}} expected-error {{in a checked scope %S format specifier requires scalar argument}}
MyPrintf("%S", w); // expected-error {{'S' conversion specifier is not supported by ISO C}} expected-error {{in a checked scope %S format specifier requires scalar argument}}
scanf("%S", w); // expected-error {{'S' conversion specifier is not supported by ISO C}} expected-error {{in a checked scope %S format specifier requires _Ptr argument}}
MyScanf("%S", w); // expected-error {{'S' conversion specifier is not supported by ISO C}} expected-error {{in a checked scope %S format specifier requires _Ptr argument}}

int i;
printf("%*d", 123456789, i);

printf("%*d"); // expected-error {{'*' specified field width is missing a matching 'int' argument}}
MyPrintf("%*d"); // expected-error {{'*' specified field width is missing a matching 'int' argument}}
scanf("%*d"); // Note: This is safe because * indicates the data is to be read from the stream but ignored (i.e. it is not stored in the location pointed by an argument).
MyScanf("%*d"); // Note: This is safe because * indicates the data is to be read from the stream but ignored (i.e. it is not stored in the location pointed by an argument).

printf("%.*d", 123456789, i);

printf("%.*d"); // expected-error {{'.*' specified field precision is missing a matching 'int' argument}}
MyPrintf("%.*d"); // expected-error {{'.*' specified field precision is missing a matching 'int' argument}}
scanf("%.*d"); // expected-error {{invalid conversion specifier '.'}}
Expand Down Expand Up @@ -224,6 +301,8 @@ _Checked {
int MyPrintf_NoFormatAttr(const char *format : itype(_Nt_array_ptr<const char>), ...);

void f5(_Nt_array_ptr<char> p) {
// A custom variadic function that does not have an __attribute__((format))
// is not allowed in checked scope.
_Checked {
MyPrintf_NoFormatAttr("%s", "abc"); // expected-error {{cannot use this variable arguments function in a checked scope or function}}
}
Expand Down