xref: /llvm-project/clang/lib/StaticAnalyzer/Checkers/StackAddrEscapeChecker.cpp (revision 3a02247dc9e39bc62c5ca6bbe6a3c34d746b5407)
1 //=== StackAddrEscapeChecker.cpp ----------------------------------*- C++ -*--//
2 //
3 //                     The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 //
10 // This file defines stack address leak checker, which checks if an invalid
11 // stack address is stored into a global or heap location. See CERT DCL30-C.
12 //
13 //===----------------------------------------------------------------------===//
14 
15 #include "ClangSACheckers.h"
16 #include "clang/AST/ExprCXX.h"
17 #include "clang/Basic/SourceManager.h"
18 #include "clang/StaticAnalyzer/Core/BugReporter/BugType.h"
19 #include "clang/StaticAnalyzer/Core/Checker.h"
20 #include "clang/StaticAnalyzer/Core/CheckerManager.h"
21 #include "clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.h"
22 #include "clang/StaticAnalyzer/Core/PathSensitive/ProgramState.h"
23 #include "llvm/ADT/SmallString.h"
24 #include "llvm/Support/raw_ostream.h"
25 using namespace clang;
26 using namespace ento;
27 
28 namespace {
29 class StackAddrEscapeChecker : public Checker< check::PreStmt<ReturnStmt>,
30                                                check::EndPath > {
31   mutable OwningPtr<BuiltinBug> BT_stackleak;
32   mutable OwningPtr<BuiltinBug> BT_returnstack;
33 
34 public:
35   void checkPreStmt(const ReturnStmt *RS, CheckerContext &C) const;
36   void checkEndPath(CheckerContext &Ctx) const;
37 private:
38   void EmitStackError(CheckerContext &C, const MemRegion *R,
39                       const Expr *RetE) const;
40   static SourceRange GenName(raw_ostream &os, const MemRegion *R,
41                              SourceManager &SM);
42 };
43 }
44 
45 SourceRange StackAddrEscapeChecker::GenName(raw_ostream &os,
46                                           const MemRegion *R,
47                                           SourceManager &SM) {
48     // Get the base region, stripping away fields and elements.
49   R = R->getBaseRegion();
50   SourceRange range;
51   os << "Address of ";
52 
53   // Check if the region is a compound literal.
54   if (const CompoundLiteralRegion* CR = dyn_cast<CompoundLiteralRegion>(R)) {
55     const CompoundLiteralExpr *CL = CR->getLiteralExpr();
56     os << "stack memory associated with a compound literal "
57           "declared on line "
58         << SM.getExpansionLineNumber(CL->getLocStart())
59         << " returned to caller";
60     range = CL->getSourceRange();
61   }
62   else if (const AllocaRegion* AR = dyn_cast<AllocaRegion>(R)) {
63     const Expr *ARE = AR->getExpr();
64     SourceLocation L = ARE->getLocStart();
65     range = ARE->getSourceRange();
66     os << "stack memory allocated by call to alloca() on line "
67        << SM.getExpansionLineNumber(L);
68   }
69   else if (const BlockDataRegion *BR = dyn_cast<BlockDataRegion>(R)) {
70     const BlockDecl *BD = BR->getCodeRegion()->getDecl();
71     SourceLocation L = BD->getLocStart();
72     range = BD->getSourceRange();
73     os << "stack-allocated block declared on line "
74        << SM.getExpansionLineNumber(L);
75   }
76   else if (const VarRegion *VR = dyn_cast<VarRegion>(R)) {
77     os << "stack memory associated with local variable '"
78        << VR->getString() << '\'';
79     range = VR->getDecl()->getSourceRange();
80   }
81   else if (const CXXTempObjectRegion *TOR = dyn_cast<CXXTempObjectRegion>(R)) {
82     os << "stack memory associated with temporary object of type '"
83        << TOR->getValueType().getAsString() << '\'';
84     range = TOR->getExpr()->getSourceRange();
85   }
86   else {
87     llvm_unreachable("Invalid region in ReturnStackAddressChecker.");
88   }
89 
90   return range;
91 }
92 
93 void StackAddrEscapeChecker::EmitStackError(CheckerContext &C, const MemRegion *R,
94                                           const Expr *RetE) const {
95   ExplodedNode *N = C.generateSink();
96 
97   if (!N)
98     return;
99 
100   if (!BT_returnstack)
101    BT_returnstack.reset(
102                  new BuiltinBug("Return of address to stack-allocated memory"));
103 
104   // Generate a report for this bug.
105   SmallString<512> buf;
106   llvm::raw_svector_ostream os(buf);
107   SourceRange range = GenName(os, R, C.getSourceManager());
108   os << " returned to caller";
109   BugReport *report = new BugReport(*BT_returnstack, os.str(), N);
110   report->addRange(RetE->getSourceRange());
111   if (range.isValid())
112     report->addRange(range);
113 
114   C.emitReport(report);
115 }
116 
117 void StackAddrEscapeChecker::checkPreStmt(const ReturnStmt *RS,
118                                           CheckerContext &C) const {
119 
120   const Expr *RetE = RS->getRetValue();
121   if (!RetE)
122     return;
123   RetE = RetE->IgnoreParens();
124 
125   const LocationContext *LCtx = C.getLocationContext();
126   SVal V = C.getState()->getSVal(RetE, LCtx);
127   const MemRegion *R = V.getAsRegion();
128 
129   if (!R)
130     return;
131 
132   const StackSpaceRegion *SS =
133     dyn_cast_or_null<StackSpaceRegion>(R->getMemorySpace());
134 
135   if (!SS)
136     return;
137 
138   // Return stack memory in an ancestor stack frame is fine.
139   const StackFrameContext *CurFrame = LCtx->getCurrentStackFrame();
140   const StackFrameContext *MemFrame = SS->getStackFrame();
141   if (MemFrame != CurFrame)
142     return;
143 
144   // Automatic reference counting automatically copies blocks.
145   if (C.getASTContext().getLangOpts().ObjCAutoRefCount &&
146       isa<BlockDataRegion>(R))
147     return;
148 
149   // Returning a record by value is fine. (In this case, the returned
150   // expression will be a copy-constructor, possibly wrapped in an
151   // ExprWithCleanups node.)
152   if (const ExprWithCleanups *Cleanup = dyn_cast<ExprWithCleanups>(RetE))
153     RetE = Cleanup->getSubExpr();
154   if (isa<CXXConstructExpr>(RetE) && RetE->getType()->isRecordType())
155     return;
156 
157   EmitStackError(C, R, RetE);
158 }
159 
160 void StackAddrEscapeChecker::checkEndPath(CheckerContext &Ctx) const {
161   ProgramStateRef state = Ctx.getState();
162 
163   // Iterate over all bindings to global variables and see if it contains
164   // a memory region in the stack space.
165   class CallBack : public StoreManager::BindingsHandler {
166   private:
167     CheckerContext &Ctx;
168     const StackFrameContext *CurSFC;
169   public:
170     SmallVector<std::pair<const MemRegion*, const MemRegion*>, 10> V;
171 
172     CallBack(CheckerContext &CC) :
173       Ctx(CC),
174       CurSFC(CC.getLocationContext()->getCurrentStackFrame())
175     {}
176 
177     bool HandleBinding(StoreManager &SMgr, Store store,
178                        const MemRegion *region, SVal val) {
179 
180       if (!isa<GlobalsSpaceRegion>(region->getMemorySpace()))
181         return true;
182 
183       const MemRegion *vR = val.getAsRegion();
184       if (!vR)
185         return true;
186 
187       // Under automated retain release, it is okay to assign a block
188       // directly to a global variable.
189       if (Ctx.getASTContext().getLangOpts().ObjCAutoRefCount &&
190           isa<BlockDataRegion>(vR))
191         return true;
192 
193       if (const StackSpaceRegion *SSR =
194           dyn_cast<StackSpaceRegion>(vR->getMemorySpace())) {
195         // If the global variable holds a location in the current stack frame,
196         // record the binding to emit a warning.
197         if (SSR->getStackFrame() == CurSFC)
198           V.push_back(std::make_pair(region, vR));
199       }
200 
201       return true;
202     }
203   };
204 
205   CallBack cb(Ctx);
206   state->getStateManager().getStoreManager().iterBindings(state->getStore(),cb);
207 
208   if (cb.V.empty())
209     return;
210 
211   // Generate an error node.
212   ExplodedNode *N = Ctx.addTransition(state);
213   if (!N)
214     return;
215 
216   if (!BT_stackleak)
217     BT_stackleak.reset(
218       new BuiltinBug("Stack address stored into global variable",
219                      "Stack address was saved into a global variable. "
220                      "This is dangerous because the address will become "
221                      "invalid after returning from the function"));
222 
223   for (unsigned i = 0, e = cb.V.size(); i != e; ++i) {
224     // Generate a report for this bug.
225     SmallString<512> buf;
226     llvm::raw_svector_ostream os(buf);
227     SourceRange range = GenName(os, cb.V[i].second,
228                                 Ctx.getSourceManager());
229     os << " is still referred to by the global variable '";
230     const VarRegion *VR = cast<VarRegion>(cb.V[i].first->getBaseRegion());
231     os << *VR->getDecl()
232        << "' upon returning to the caller.  This will be a dangling reference";
233     BugReport *report = new BugReport(*BT_stackleak, os.str(), N);
234     if (range.isValid())
235       report->addRange(range);
236 
237     Ctx.emitReport(report);
238   }
239 }
240 
241 void ento::registerStackAddrEscapeChecker(CheckerManager &mgr) {
242   mgr.registerChecker<StackAddrEscapeChecker>();
243 }
244