clang  14.0.0git
VforkChecker.cpp
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1 //===- VforkChecker.cpp -------- Vfork usage checks --------------*- C++ -*-==//
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 // This file defines vfork checker which checks for dangerous uses of vfork.
10 // Vforked process shares memory (including stack) with parent so it's
11 // range of actions is significantly limited: can't write variables,
12 // can't call functions not in whitelist, etc. For more details, see
13 // http://man7.org/linux/man-pages/man2/vfork.2.html
14 //
15 // This checker checks for prohibited constructs in vforked process.
16 // The state transition diagram:
17 // PARENT ---(vfork() == 0)--> CHILD
18 // |
19 // --(*p = ...)--> bug
20 // |
21 // --foo()--> bug
22 // |
23 // --return--> bug
24 //
25 //===----------------------------------------------------------------------===//
26 
37 #include "clang/AST/ParentMap.h"
38 
39 using namespace clang;
40 using namespace ento;
41 
42 namespace {
43 
44 class VforkChecker : public Checker<check::PreCall, check::PostCall,
45  check::Bind, check::PreStmt<ReturnStmt>> {
46  mutable std::unique_ptr<BuiltinBug> BT;
47  mutable llvm::SmallSet<const IdentifierInfo *, 10> VforkWhitelist;
48  mutable const IdentifierInfo *II_vfork;
49 
50  static bool isChildProcess(const ProgramStateRef State);
51 
52  bool isVforkCall(const Decl *D, CheckerContext &C) const;
53  bool isCallWhitelisted(const IdentifierInfo *II, CheckerContext &C) const;
54 
55  void reportBug(const char *What, CheckerContext &C,
56  const char *Details = nullptr) const;
57 
58 public:
59  VforkChecker() : II_vfork(nullptr) {}
60 
61  void checkPreCall(const CallEvent &Call, CheckerContext &C) const;
62  void checkPostCall(const CallEvent &Call, CheckerContext &C) const;
63  void checkBind(SVal L, SVal V, const Stmt *S, CheckerContext &C) const;
64  void checkPreStmt(const ReturnStmt *RS, CheckerContext &C) const;
65 };
66 
67 } // end anonymous namespace
68 
69 // This trait holds region of variable that is assigned with vfork's
70 // return value (this is the only region child is allowed to write).
71 // VFORK_RESULT_INVALID means that we are in parent process.
72 // VFORK_RESULT_NONE means that vfork's return value hasn't been assigned.
73 // Other values point to valid regions.
74 REGISTER_TRAIT_WITH_PROGRAMSTATE(VforkResultRegion, const void *)
75 #define VFORK_RESULT_INVALID 0
76 #define VFORK_RESULT_NONE ((void *)(uintptr_t)1)
77 
78 bool VforkChecker::isChildProcess(const ProgramStateRef State) {
79  return State->get<VforkResultRegion>() != VFORK_RESULT_INVALID;
80 }
81 
82 bool VforkChecker::isVforkCall(const Decl *D, CheckerContext &C) const {
83  auto FD = dyn_cast_or_null<FunctionDecl>(D);
84  if (!FD || !C.isCLibraryFunction(FD))
85  return false;
86 
87  if (!II_vfork) {
88  ASTContext &AC = C.getASTContext();
89  II_vfork = &AC.Idents.get("vfork");
90  }
91 
92  return FD->getIdentifier() == II_vfork;
93 }
94 
95 // Returns true iff ok to call function after successful vfork.
96 bool VforkChecker::isCallWhitelisted(const IdentifierInfo *II,
97  CheckerContext &C) const {
98  if (VforkWhitelist.empty()) {
99  // According to manpage.
100  const char *ids[] = {
101  "_Exit",
102  "_exit",
103  "execl",
104  "execle",
105  "execlp",
106  "execv",
107  "execve",
108  "execvp",
109  "execvpe",
110  nullptr
111  };
112 
113  ASTContext &AC = C.getASTContext();
114  for (const char **id = ids; *id; ++id)
115  VforkWhitelist.insert(&AC.Idents.get(*id));
116  }
117 
118  return VforkWhitelist.count(II);
119 }
120 
121 void VforkChecker::reportBug(const char *What, CheckerContext &C,
122  const char *Details) const {
123  if (ExplodedNode *N = C.generateErrorNode(C.getState())) {
124  if (!BT)
125  BT.reset(new BuiltinBug(this,
126  "Dangerous construct in a vforked process"));
127 
128  SmallString<256> buf;
129  llvm::raw_svector_ostream os(buf);
130 
131  os << What << " is prohibited after a successful vfork";
132 
133  if (Details)
134  os << "; " << Details;
135 
136  auto Report = std::make_unique<PathSensitiveBugReport>(*BT, os.str(), N);
137  // TODO: mark vfork call in BugReportVisitor
138  C.emitReport(std::move(Report));
139  }
140 }
141 
142 // Detect calls to vfork and split execution appropriately.
143 void VforkChecker::checkPostCall(const CallEvent &Call,
144  CheckerContext &C) const {
145  // We can't call vfork in child so don't bother
146  // (corresponding warning has already been emitted in checkPreCall).
147  ProgramStateRef State = C.getState();
148  if (isChildProcess(State))
149  return;
150 
151  if (!isVforkCall(Call.getDecl(), C))
152  return;
153 
154  // Get return value of vfork.
155  SVal VforkRetVal = Call.getReturnValue();
157  VforkRetVal.getAs<DefinedOrUnknownSVal>();
158  if (!DVal)
159  return;
160 
161  // Get assigned variable.
162  const ParentMap &PM = C.getLocationContext()->getParentMap();
163  const Stmt *P = PM.getParentIgnoreParenCasts(Call.getOriginExpr());
164  const VarDecl *LhsDecl;
165  std::tie(LhsDecl, std::ignore) = parseAssignment(P);
166 
167  // Get assigned memory region.
168  MemRegionManager &M = C.getStoreManager().getRegionManager();
169  const MemRegion *LhsDeclReg =
170  LhsDecl
171  ? M.getVarRegion(LhsDecl, C.getLocationContext())
172  : (const MemRegion *)VFORK_RESULT_NONE;
173 
174  // Parent branch gets nonzero return value (according to manpage).
175  ProgramStateRef ParentState, ChildState;
176  std::tie(ParentState, ChildState) = C.getState()->assume(*DVal);
177  C.addTransition(ParentState);
178  ChildState = ChildState->set<VforkResultRegion>(LhsDeclReg);
179  C.addTransition(ChildState);
180 }
181 
182 // Prohibit calls to non-whitelist functions in child process.
183 void VforkChecker::checkPreCall(const CallEvent &Call,
184  CheckerContext &C) const {
185  ProgramStateRef State = C.getState();
186  if (isChildProcess(State)
187  && !isCallWhitelisted(Call.getCalleeIdentifier(), C))
188  reportBug("This function call", C);
189 }
190 
191 // Prohibit writes in child process (except for vfork's lhs).
192 void VforkChecker::checkBind(SVal L, SVal V, const Stmt *S,
193  CheckerContext &C) const {
194  ProgramStateRef State = C.getState();
195  if (!isChildProcess(State))
196  return;
197 
198  const MemRegion *VforkLhs =
199  static_cast<const MemRegion *>(State->get<VforkResultRegion>());
200  const MemRegion *MR = L.getAsRegion();
201 
202  // Child is allowed to modify only vfork's lhs.
203  if (!MR || MR == VforkLhs)
204  return;
205 
206  reportBug("This assignment", C);
207 }
208 
209 // Prohibit return from function in child process.
210 void VforkChecker::checkPreStmt(const ReturnStmt *RS, CheckerContext &C) const {
211  ProgramStateRef State = C.getState();
212  if (isChildProcess(State))
213  reportBug("Return", C, "call _exit() instead");
214 }
215 
216 void ento::registerVforkChecker(CheckerManager &mgr) {
217  mgr.registerChecker<VforkChecker>();
218 }
219 
220 bool ento::shouldRegisterVforkChecker(const CheckerManager &mgr) {
221  return true;
222 }
clang::IdentifierTable::get
IdentifierInfo & get(StringRef Name)
Return the identifier token info for the specified named identifier.
Definition: IdentifierTable.h:592
clang::ParentMap::getParentIgnoreParenCasts
Stmt * getParentIgnoreParenCasts(Stmt *) const
Definition: ParentMap.cpp:145
clang::ento::ProgramStateRef
IntrusiveRefCntPtr< const ProgramState > ProgramStateRef
Definition: ProgramState_Fwd.h:37
AttributeLangSupport::C
@ C
Definition: SemaDeclAttr.cpp:54
SymbolManager.h
llvm::Optional
Definition: LLVM.h:40
clang::index::SymbolRole::Call
@ Call
VFORK_RESULT_INVALID
#define VFORK_RESULT_INVALID
Definition: VforkChecker.cpp:75
REGISTER_TRAIT_WITH_PROGRAMSTATE
#define REGISTER_TRAIT_WITH_PROGRAMSTATE(Name, Type)
Declares a program state trait for type Type called Name, and introduce a type named NameTy.
Definition: ProgramStateTrait.h:33
CallEvent.h
clang::ento::parseAssignment
std::pair< const clang::VarDecl *, const clang::Expr * > parseAssignment(const Stmt *S)
Definition: CheckerHelpers.cpp:81
V
#define V(N, I)
Definition: ASTContext.h:3121
BuiltinCheckerRegistration.h
CheckerManager.h
clang::ASTContext
Holds long-lived AST nodes (such as types and decls) that can be referred to throughout the semantic ...
Definition: ASTContext.h:212
llvm::SmallString
Definition: LLVM.h:37
clang::VarDecl
Represents a variable declaration or definition.
Definition: Decl.h:876
clang::ParentMap
Definition: ParentMap.h:20
VFORK_RESULT_NONE
#define VFORK_RESULT_NONE
Definition: VforkChecker.cpp:76
P
StringRef P
Definition: ASTMatchersInternal.cpp:563
BugType.h
clang::ASTContext::Idents
IdentifierTable & Idents
Definition: ASTContext.h:648
clang::Decl
Decl - This represents one declaration (or definition), e.g.
Definition: DeclBase.h:89
State
LineState State
Definition: UnwrappedLineFormatter.cpp:986
clang::IdentifierInfo
One of these records is kept for each identifier that is lexed.
Definition: IdentifierTable.h:84
CheckerContext.h
ProgramState.h
Checker.h
ParentMap.h
clang
Definition: CalledOnceCheck.h:17
clang::Stmt
Stmt - This represents one statement.
Definition: Stmt.h:69
CheckerHelpers.h
ProgramStateTrait.h
clang::ReturnStmt
ReturnStmt - This represents a return, optionally of an expression: return; return 4;.
Definition: Stmt.h:2760