StringLiteralWithEmbeddedNulCheck.cpp
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//===--- StringLiteralWithEmbeddedNulCheck.cpp - clang-tidy----------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
#include "StringLiteralWithEmbeddedNulCheck.h"
#include "clang/AST/ASTContext.h"
#include "clang/ASTMatchers/ASTMatchFinder.h"
using namespace clang::ast_matchers;
namespace clang {
namespace tidy {
namespace bugprone {
namespace {
AST_MATCHER(StringLiteral, containsNul) {
for (size_t i = 0; i < Node.getLength(); ++i)
if (Node.getCodeUnit(i) == '\0')
return true;
return false;
}
} // namespace
void StringLiteralWithEmbeddedNulCheck::registerMatchers(MatchFinder *Finder) {
// Match a string that contains embedded NUL character. Extra-checks are
// applied in |check| to find incorrectly escaped characters.
Finder->addMatcher(stringLiteral(containsNul()).bind("strlit"), this);
// The remaining checks only apply to C++.
if (!getLangOpts().CPlusPlus)
return;
const auto StrLitWithNul =
ignoringParenImpCasts(stringLiteral(containsNul()).bind("truncated"));
// Match string constructor.
const auto StringConstructorExpr = expr(anyOf(
cxxConstructExpr(argumentCountIs(1),
hasDeclaration(cxxMethodDecl(hasName("basic_string")))),
// If present, the second argument is the alloc object which must not
// be present explicitly.
cxxConstructExpr(argumentCountIs(2),
hasDeclaration(cxxMethodDecl(hasName("basic_string"))),
hasArgument(1, cxxDefaultArgExpr()))));
// Detect passing a suspicious string literal to a string constructor.
// example: std::string str = "abc\0def";
Finder->addMatcher(traverse(TK_AsIs,
cxxConstructExpr(StringConstructorExpr, hasArgument(0, StrLitWithNul))),
this);
// Detect passing a suspicious string literal through an overloaded operator.
Finder->addMatcher(cxxOperatorCallExpr(hasAnyArgument(StrLitWithNul)), this);
}
void StringLiteralWithEmbeddedNulCheck::check(
const MatchFinder::MatchResult &Result) {
if (const auto *SL = Result.Nodes.getNodeAs<StringLiteral>("strlit")) {
for (size_t Offset = 0, Length = SL->getLength(); Offset < Length;
++Offset) {
// Find a sequence of character like "\0x12".
if (Offset + 3 < Length && SL->getCodeUnit(Offset) == '\0' &&
SL->getCodeUnit(Offset + 1) == 'x' &&
isDigit(SL->getCodeUnit(Offset + 2)) &&
isDigit(SL->getCodeUnit(Offset + 3))) {
diag(SL->getBeginLoc(), "suspicious embedded NUL character");
return;
}
}
}
if (const auto *SL = Result.Nodes.getNodeAs<StringLiteral>("truncated")) {
diag(SL->getBeginLoc(),
"truncated string literal with embedded NUL character");
}
}
} // namespace bugprone
} // namespace tidy
} // namespace clang