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//===--- ProperlySeededRandomGeneratorCheck.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 "ProperlySeededRandomGeneratorCheck.h"
#include "clang/AST/ASTContext.h"
#include "clang/ASTMatchers/ASTMatchFinder.h"
#include "llvm/ADT/STLExtras.h"
using namespace clang::ast_matchers;
namespace clang::tidy::cert {
ProperlySeededRandomGeneratorCheck::ProperlySeededRandomGeneratorCheck(
StringRef Name, ClangTidyContext *Context)
: ClangTidyCheck(Name, Context),
RawDisallowedSeedTypes(
Options.get("DisallowedSeedTypes", "time_t,std::time_t")) {
StringRef(RawDisallowedSeedTypes).split(DisallowedSeedTypes, ',');
}
void ProperlySeededRandomGeneratorCheck::storeOptions(
ClangTidyOptions::OptionMap &Opts) {
Options.store(Opts, "DisallowedSeedTypes", RawDisallowedSeedTypes);
}
void ProperlySeededRandomGeneratorCheck::registerMatchers(MatchFinder *Finder) {
auto RandomGeneratorEngineDecl = cxxRecordDecl(hasAnyName(
"::std::linear_congruential_engine", "::std::mersenne_twister_engine",
"::std::subtract_with_carry_engine", "::std::discard_block_engine",
"::std::independent_bits_engine", "::std::shuffle_order_engine"));
auto RandomGeneratorEngineTypeMatcher = hasType(hasUnqualifiedDesugaredType(
recordType(hasDeclaration(RandomGeneratorEngineDecl))));
// std::mt19937 engine;
// engine.seed();
// ^
// engine.seed(1);
// ^
// const int x = 1;
// engine.seed(x);
// ^
Finder->addMatcher(
cxxMemberCallExpr(
has(memberExpr(has(declRefExpr(RandomGeneratorEngineTypeMatcher)),
member(hasName("seed")),
unless(hasDescendant(cxxThisExpr())))))
.bind("seed"),
this);
// std::mt19937 engine;
// ^
// std::mt19937 engine(1);
// ^
// const int x = 1;
// std::mt19937 engine(x);
// ^
Finder->addMatcher(
traverse(TK_AsIs,
cxxConstructExpr(RandomGeneratorEngineTypeMatcher).bind("ctor")),
this);
// srand();
// ^
// const int x = 1;
// srand(x);
// ^
Finder->addMatcher(
callExpr(callee(functionDecl(hasAnyName("::srand", "::std::srand"))))
.bind("srand"),
this);
}
void ProperlySeededRandomGeneratorCheck::check(
const MatchFinder::MatchResult &Result) {
const auto *Ctor = Result.Nodes.getNodeAs<CXXConstructExpr>("ctor");
if (Ctor)
checkSeed(Result, Ctor);
const auto *Func = Result.Nodes.getNodeAs<CXXMemberCallExpr>("seed");
if (Func)
checkSeed(Result, Func);
const auto *Srand = Result.Nodes.getNodeAs<CallExpr>("srand");
if (Srand)
checkSeed(Result, Srand);
}
template <class T>
void ProperlySeededRandomGeneratorCheck::checkSeed(
const MatchFinder::MatchResult &Result, const T *Func) {
if (Func->getNumArgs() == 0 || Func->getArg(0)->isDefaultArgument()) {
diag(Func->getExprLoc(),
"random number generator seeded with a default argument will generate "
"a predictable sequence of values");
return;
}
Expr::EvalResult EVResult;
if (Func->getArg(0)->EvaluateAsInt(EVResult, *Result.Context)) {
diag(Func->getExprLoc(),
"random number generator seeded with a constant value will generate a "
"predictable sequence of values");
return;
}
const std::string SeedType(
Func->getArg(0)->IgnoreCasts()->getType().getAsString());
if (llvm::is_contained(DisallowedSeedTypes, SeedType)) {
diag(Func->getExprLoc(),
"random number generator seeded with a disallowed source of seed "
"value will generate a predictable sequence of values");
return;
}
}
} // namespace clang::tidy::cert
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