1 //===--- SuspiciousStringCompareCheck.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 "SuspiciousStringCompareCheck.h"
10 #include "../utils/Matchers.h"
11 #include "../utils/OptionsUtils.h"
12 #include "clang/AST/ASTContext.h"
13 #include "clang/ASTMatchers/ASTMatchFinder.h"
14 #include "clang/Lex/Lexer.h"
15
16 using namespace clang::ast_matchers;
17
18 namespace clang::tidy::bugprone {
19
20 // Semicolon separated list of known string compare-like functions. The list
21 // must ends with a semicolon.
22 static const char KnownStringCompareFunctions[] = "__builtin_memcmp;"
23 "__builtin_strcasecmp;"
24 "__builtin_strcmp;"
25 "__builtin_strncasecmp;"
26 "__builtin_strncmp;"
27 "_mbscmp;"
28 "_mbscmp_l;"
29 "_mbsicmp;"
30 "_mbsicmp_l;"
31 "_mbsnbcmp;"
32 "_mbsnbcmp_l;"
33 "_mbsnbicmp;"
34 "_mbsnbicmp_l;"
35 "_mbsncmp;"
36 "_mbsncmp_l;"
37 "_mbsnicmp;"
38 "_mbsnicmp_l;"
39 "_memicmp;"
40 "_memicmp_l;"
41 "_stricmp;"
42 "_stricmp_l;"
43 "_strnicmp;"
44 "_strnicmp_l;"
45 "_wcsicmp;"
46 "_wcsicmp_l;"
47 "_wcsnicmp;"
48 "_wcsnicmp_l;"
49 "lstrcmp;"
50 "lstrcmpi;"
51 "memcmp;"
52 "memicmp;"
53 "strcasecmp;"
54 "strcmp;"
55 "strcmpi;"
56 "stricmp;"
57 "strncasecmp;"
58 "strncmp;"
59 "strnicmp;"
60 "wcscasecmp;"
61 "wcscmp;"
62 "wcsicmp;"
63 "wcsncmp;"
64 "wcsnicmp;"
65 "wmemcmp;";
66
SuspiciousStringCompareCheck(StringRef Name,ClangTidyContext * Context)67 SuspiciousStringCompareCheck::SuspiciousStringCompareCheck(
68 StringRef Name, ClangTidyContext *Context)
69 : ClangTidyCheck(Name, Context),
70 WarnOnImplicitComparison(Options.get("WarnOnImplicitComparison", true)),
71 WarnOnLogicalNotComparison(
72 Options.get("WarnOnLogicalNotComparison", false)),
73 StringCompareLikeFunctions(
74 Options.get("StringCompareLikeFunctions", "")) {}
75
storeOptions(ClangTidyOptions::OptionMap & Opts)76 void SuspiciousStringCompareCheck::storeOptions(
77 ClangTidyOptions::OptionMap &Opts) {
78 Options.store(Opts, "WarnOnImplicitComparison", WarnOnImplicitComparison);
79 Options.store(Opts, "WarnOnLogicalNotComparison", WarnOnLogicalNotComparison);
80 Options.store(Opts, "StringCompareLikeFunctions", StringCompareLikeFunctions);
81 }
82
registerMatchers(MatchFinder * Finder)83 void SuspiciousStringCompareCheck::registerMatchers(MatchFinder *Finder) {
84 // Match relational operators.
85 const auto ComparisonUnaryOperator = unaryOperator(hasOperatorName("!"));
86 const auto ComparisonBinaryOperator = binaryOperator(isComparisonOperator());
87 const auto ComparisonOperator =
88 expr(anyOf(ComparisonUnaryOperator, ComparisonBinaryOperator));
89
90 // Add the list of known string compare-like functions and add user-defined
91 // functions.
92 std::vector<StringRef> FunctionNames = utils::options::parseListPair(
93 KnownStringCompareFunctions, StringCompareLikeFunctions);
94
95 // Match a call to a string compare functions.
96 const auto FunctionCompareDecl =
97 functionDecl(hasAnyName(FunctionNames)).bind("decl");
98 const auto DirectStringCompareCallExpr =
99 callExpr(hasDeclaration(FunctionCompareDecl)).bind("call");
100 const auto MacroStringCompareCallExpr = conditionalOperator(anyOf(
101 hasTrueExpression(ignoringParenImpCasts(DirectStringCompareCallExpr)),
102 hasFalseExpression(ignoringParenImpCasts(DirectStringCompareCallExpr))));
103 // The implicit cast is not present in C.
104 const auto StringCompareCallExpr = ignoringParenImpCasts(
105 anyOf(DirectStringCompareCallExpr, MacroStringCompareCallExpr));
106
107 if (WarnOnImplicitComparison) {
108 // Detect suspicious calls to string compare:
109 // 'if (strcmp())' -> 'if (strcmp() != 0)'
110 Finder->addMatcher(
111 stmt(anyOf(mapAnyOf(ifStmt, whileStmt, doStmt, forStmt)
112 .with(hasCondition(StringCompareCallExpr)),
113 binaryOperator(hasAnyOperatorName("&&", "||"),
114 hasEitherOperand(StringCompareCallExpr))))
115 .bind("missing-comparison"),
116 this);
117 }
118
119 if (WarnOnLogicalNotComparison) {
120 // Detect suspicious calls to string compared with '!' operator:
121 // 'if (!strcmp())' -> 'if (strcmp() == 0)'
122 Finder->addMatcher(unaryOperator(hasOperatorName("!"),
123 hasUnaryOperand(ignoringParenImpCasts(
124 StringCompareCallExpr)))
125 .bind("logical-not-comparison"),
126 this);
127 }
128
129 // Detect suspicious cast to an inconsistent type (i.e. not integer type).
130 Finder->addMatcher(
131 traverse(TK_AsIs,
132 implicitCastExpr(unless(hasType(isInteger())),
133 hasSourceExpression(StringCompareCallExpr))
134 .bind("invalid-conversion")),
135 this);
136
137 // Detect suspicious operator with string compare function as operand.
138 Finder->addMatcher(
139 binaryOperator(unless(anyOf(isComparisonOperator(), hasOperatorName("&&"),
140 hasOperatorName("||"), hasOperatorName("="))),
141 hasEitherOperand(StringCompareCallExpr))
142 .bind("suspicious-operator"),
143 this);
144
145 // Detect comparison to invalid constant: 'strcmp() == -1'.
146 const auto InvalidLiteral = ignoringParenImpCasts(
147 anyOf(integerLiteral(unless(equals(0))),
148 unaryOperator(
149 hasOperatorName("-"),
150 has(ignoringParenImpCasts(integerLiteral(unless(equals(0)))))),
151 characterLiteral(), cxxBoolLiteral()));
152
153 Finder->addMatcher(
154 binaryOperator(isComparisonOperator(),
155 hasOperands(StringCompareCallExpr, InvalidLiteral))
156 .bind("invalid-comparison"),
157 this);
158 }
159
check(const MatchFinder::MatchResult & Result)160 void SuspiciousStringCompareCheck::check(
161 const MatchFinder::MatchResult &Result) {
162 const auto *Decl = Result.Nodes.getNodeAs<FunctionDecl>("decl");
163 const auto *Call = Result.Nodes.getNodeAs<CallExpr>("call");
164 assert(Decl != nullptr && Call != nullptr);
165
166 if (Result.Nodes.getNodeAs<Stmt>("missing-comparison")) {
167 SourceLocation EndLoc = Lexer::getLocForEndOfToken(
168 Call->getRParenLoc(), 0, Result.Context->getSourceManager(),
169 getLangOpts());
170
171 diag(Call->getBeginLoc(),
172 "function %0 is called without explicitly comparing result")
173 << Decl << FixItHint::CreateInsertion(EndLoc, " != 0");
174 }
175
176 if (const auto *E = Result.Nodes.getNodeAs<Expr>("logical-not-comparison")) {
177 SourceLocation EndLoc = Lexer::getLocForEndOfToken(
178 Call->getRParenLoc(), 0, Result.Context->getSourceManager(),
179 getLangOpts());
180 SourceLocation NotLoc = E->getBeginLoc();
181
182 diag(Call->getBeginLoc(),
183 "function %0 is compared using logical not operator")
184 << Decl
185 << FixItHint::CreateRemoval(
186 CharSourceRange::getTokenRange(NotLoc, NotLoc))
187 << FixItHint::CreateInsertion(EndLoc, " == 0");
188 }
189
190 if (Result.Nodes.getNodeAs<Stmt>("invalid-comparison")) {
191 diag(Call->getBeginLoc(),
192 "function %0 is compared to a suspicious constant")
193 << Decl;
194 }
195
196 if (const auto *BinOp =
197 Result.Nodes.getNodeAs<BinaryOperator>("suspicious-operator")) {
198 diag(Call->getBeginLoc(), "results of function %0 used by operator '%1'")
199 << Decl << BinOp->getOpcodeStr();
200 }
201
202 if (Result.Nodes.getNodeAs<Stmt>("invalid-conversion")) {
203 diag(Call->getBeginLoc(), "function %0 has suspicious implicit cast")
204 << Decl;
205 }
206 }
207
208 } // namespace clang::tidy::bugprone
209