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[clang] Bounds checking on unclosed parentheses, brackets or braces in Expanded Tokens #69849

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[clang] Bounds checking on unclosed parentheses, brackets or braces in Expanded Tokens #69849

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25 changes: 19 additions & 6 deletions clang/lib/Tooling/Syntax/Tokens.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -286,9 +286,13 @@ TokenBuffer::spelledForExpandedToken(const syntax::Token *Expanded) const {
});
// Our token could only be produced by the previous mapping.
if (It == File.Mappings.begin()) {
// No previous mapping, no need to modify offsets.
return {&File.SpelledTokens[ExpandedIndex - File.BeginExpanded],
/*Mapping=*/nullptr};
const auto offset = ExpandedIndex - File.BeginExpanded;
// Bounds check so parsing an unclosed parenthesis, brackets or braces do
// not result in UB.
if (offset >= File.SpelledTokens.size()) {
return {nullptr, nullptr};
}
return {&File.SpelledTokens[offset], /*Mapping=*/nullptr};
}
--It; // 'It' now points to last mapping that started before our token.

Expand All @@ -298,9 +302,12 @@ TokenBuffer::spelledForExpandedToken(const syntax::Token *Expanded) const {

// Not part of the mapping, use the index from previous mapping to compute the
// corresponding spelled token.
return {
&File.SpelledTokens[It->EndSpelled + (ExpandedIndex - It->EndExpanded)],
/*Mapping=*/nullptr};
const auto offset = It->EndSpelled + (ExpandedIndex - It->EndExpanded);
// This index can also result in UB when parsing unclosed tokens.
if (offset >= File.SpelledTokens.size()) {
return {nullptr, nullptr};
}
return {&File.SpelledTokens[offset], /*Mapping=*/nullptr};
}

const TokenBuffer::Mapping *
Expand Down Expand Up @@ -410,6 +417,12 @@ TokenBuffer::spelledForExpanded(llvm::ArrayRef<syntax::Token> Expanded) const {
auto [FirstSpelled, FirstMapping] = spelledForExpandedToken(First);
auto [LastSpelled, LastMapping] = spelledForExpandedToken(Last);

// If there was an unclosed token, FirstSpelled or LastSpelled is null and the
// operation shouldn't continue.
if (FirstSpelled == nullptr || LastSpelled == nullptr) {
return std::nullopt;
};

FileID FID = SourceMgr->getFileID(FirstSpelled->location());
// FIXME: Handle multi-file changes by trying to map onto a common root.
if (FID != SourceMgr->getFileID(LastSpelled->location()))
Expand Down
11 changes: 11 additions & 0 deletions clang/unittests/Tooling/Syntax/TokensTest.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -585,6 +585,17 @@ TEST_F(TokenCollectorTest, DelayedParsing) {
EXPECT_THAT(collectAndDump(Code), StartsWith(ExpectedTokens));
}

TEST_F(TokenCollectorTest, UnclosedToken) {
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I started looking at this to try and make some progress towards getting this landed. However, when running this test locally, I'm not seeing either of the branches added to spelledForExpandedToken() being taken.

Am I missing something, or is this test not exercising the intended codepath?

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Indeed, it looks like TokenBuffer::spelledForExpanded() (which is the only call site of spelledForExpandedToken()) is not called by anything currently in this test.

To exercise spelledForExpanded(), we will need to make an explicit call to it, the way a number of other tests in this file do.

llvm::StringLiteral Code = R"cpp(
int main() {
// this should not result in a segfault or UB.
)cpp";
std::string ExpectedTokens =
"expanded tokens:\n int main ( ) {\nfile './input.cpp'\n spelled "
"tokens:\n int main ( ) {\n no mappings.\n";
EXPECT_THAT(collectAndDump(Code), StartsWith(ExpectedTokens));
}

TEST_F(TokenCollectorTest, MultiFile) {
addFile("./foo.h", R"cpp(
#define ADD(X, Y) X+Y
Expand Down