1 //===--- ProperlySeededRandomGeneratorCheck.cpp - clang-tidy---------------===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8
9 #include "ProperlySeededRandomGeneratorCheck.h"
10 #include "clang/AST/ASTContext.h"
11 #include "clang/ASTMatchers/ASTMatchFinder.h"
12 #include "llvm/ADT/STLExtras.h"
13
14 using namespace clang::ast_matchers;
15
16 namespace clang::tidy::cert {
17
ProperlySeededRandomGeneratorCheck(StringRef Name,ClangTidyContext * Context)18 ProperlySeededRandomGeneratorCheck::ProperlySeededRandomGeneratorCheck(
19 StringRef Name, ClangTidyContext *Context)
20 : ClangTidyCheck(Name, Context),
21 RawDisallowedSeedTypes(
22 Options.get("DisallowedSeedTypes", "time_t,std::time_t")) {
23 StringRef(RawDisallowedSeedTypes).split(DisallowedSeedTypes, ',');
24 }
25
storeOptions(ClangTidyOptions::OptionMap & Opts)26 void ProperlySeededRandomGeneratorCheck::storeOptions(
27 ClangTidyOptions::OptionMap &Opts) {
28 Options.store(Opts, "DisallowedSeedTypes", RawDisallowedSeedTypes);
29 }
30
registerMatchers(MatchFinder * Finder)31 void ProperlySeededRandomGeneratorCheck::registerMatchers(MatchFinder *Finder) {
32 auto RandomGeneratorEngineDecl = cxxRecordDecl(hasAnyName(
33 "::std::linear_congruential_engine", "::std::mersenne_twister_engine",
34 "::std::subtract_with_carry_engine", "::std::discard_block_engine",
35 "::std::independent_bits_engine", "::std::shuffle_order_engine"));
36 auto RandomGeneratorEngineTypeMatcher = hasType(hasUnqualifiedDesugaredType(
37 recordType(hasDeclaration(RandomGeneratorEngineDecl))));
38
39 // std::mt19937 engine;
40 // engine.seed();
41 // ^
42 // engine.seed(1);
43 // ^
44 // const int x = 1;
45 // engine.seed(x);
46 // ^
47 Finder->addMatcher(
48 cxxMemberCallExpr(
49 has(memberExpr(has(declRefExpr(RandomGeneratorEngineTypeMatcher)),
50 member(hasName("seed")),
51 unless(hasDescendant(cxxThisExpr())))))
52 .bind("seed"),
53 this);
54
55 // std::mt19937 engine;
56 // ^
57 // std::mt19937 engine(1);
58 // ^
59 // const int x = 1;
60 // std::mt19937 engine(x);
61 // ^
62 Finder->addMatcher(
63 traverse(TK_AsIs,
64 cxxConstructExpr(RandomGeneratorEngineTypeMatcher).bind("ctor")),
65 this);
66
67 // srand();
68 // ^
69 // const int x = 1;
70 // srand(x);
71 // ^
72 Finder->addMatcher(
73 callExpr(callee(functionDecl(hasAnyName("::srand", "::std::srand"))))
74 .bind("srand"),
75 this);
76 }
77
check(const MatchFinder::MatchResult & Result)78 void ProperlySeededRandomGeneratorCheck::check(
79 const MatchFinder::MatchResult &Result) {
80 const auto *Ctor = Result.Nodes.getNodeAs<CXXConstructExpr>("ctor");
81 if (Ctor)
82 checkSeed(Result, Ctor);
83
84 const auto *Func = Result.Nodes.getNodeAs<CXXMemberCallExpr>("seed");
85 if (Func)
86 checkSeed(Result, Func);
87
88 const auto *Srand = Result.Nodes.getNodeAs<CallExpr>("srand");
89 if (Srand)
90 checkSeed(Result, Srand);
91 }
92
93 template <class T>
checkSeed(const MatchFinder::MatchResult & Result,const T * Func)94 void ProperlySeededRandomGeneratorCheck::checkSeed(
95 const MatchFinder::MatchResult &Result, const T *Func) {
96 if (Func->getNumArgs() == 0 || Func->getArg(0)->isDefaultArgument()) {
97 diag(Func->getExprLoc(),
98 "random number generator seeded with a default argument will generate "
99 "a predictable sequence of values");
100 return;
101 }
102
103 Expr::EvalResult EVResult;
104 if (Func->getArg(0)->EvaluateAsInt(EVResult, *Result.Context)) {
105 diag(Func->getExprLoc(),
106 "random number generator seeded with a constant value will generate a "
107 "predictable sequence of values");
108 return;
109 }
110
111 const std::string SeedType(
112 Func->getArg(0)->IgnoreCasts()->getType().getAsString());
113 if (llvm::is_contained(DisallowedSeedTypes, SeedType)) {
114 diag(Func->getExprLoc(),
115 "random number generator seeded with a disallowed source of seed "
116 "value will generate a predictable sequence of values");
117 return;
118 }
119 }
120
121 } // namespace clang::tidy::cert
122