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/StaticAnalyzer/Core/Checker.h"
17 #include "clang/StaticAnalyzer/Core/CheckerManager.h"
18 #include "clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.h"
19 #include "clang/StaticAnalyzer/Core/BugReporter/BugType.h"
20 #include "clang/StaticAnalyzer/Core/PathSensitive/ProgramState.h"
21 #include "clang/Basic/SourceManager.h"
22 #include "llvm/ADT/SmallString.h"
23 using namespace clang;
24 using namespace ento;
25
26 namespace {
27 class StackAddrEscapeChecker : public Checker< check::PreStmt<ReturnStmt>,
28 check::EndPath > {
29 mutable OwningPtr<BuiltinBug> BT_stackleak;
30 mutable OwningPtr<BuiltinBug> BT_returnstack;
31
32 public:
33 void checkPreStmt(const ReturnStmt *RS, CheckerContext &C) const;
34 void checkEndPath(CheckerContext &Ctx) const;
35 private:
36 void EmitStackError(CheckerContext &C, const MemRegion *R,
37 const Expr *RetE) const;
38 static SourceRange GenName(raw_ostream &os, const MemRegion *R,
39 SourceManager &SM);
40 };
41 }
42
GenName(raw_ostream & os,const MemRegion * R,SourceManager & SM)43 SourceRange StackAddrEscapeChecker::GenName(raw_ostream &os,
44 const MemRegion *R,
45 SourceManager &SM) {
46 // Get the base region, stripping away fields and elements.
47 R = R->getBaseRegion();
48 SourceRange range;
49 os << "Address of ";
50
51 // Check if the region is a compound literal.
52 if (const CompoundLiteralRegion* CR = dyn_cast<CompoundLiteralRegion>(R)) {
53 const CompoundLiteralExpr *CL = CR->getLiteralExpr();
54 os << "stack memory associated with a compound literal "
55 "declared on line "
56 << SM.getExpansionLineNumber(CL->getLocStart())
57 << " returned to caller";
58 range = CL->getSourceRange();
59 }
60 else if (const AllocaRegion* AR = dyn_cast<AllocaRegion>(R)) {
61 const Expr *ARE = AR->getExpr();
62 SourceLocation L = ARE->getLocStart();
63 range = ARE->getSourceRange();
64 os << "stack memory allocated by call to alloca() on line "
65 << SM.getExpansionLineNumber(L);
66 }
67 else if (const BlockDataRegion *BR = dyn_cast<BlockDataRegion>(R)) {
68 const BlockDecl *BD = BR->getCodeRegion()->getDecl();
69 SourceLocation L = BD->getLocStart();
70 range = BD->getSourceRange();
71 os << "stack-allocated block declared on line "
72 << SM.getExpansionLineNumber(L);
73 }
74 else if (const VarRegion *VR = dyn_cast<VarRegion>(R)) {
75 os << "stack memory associated with local variable '"
76 << VR->getString() << '\'';
77 range = VR->getDecl()->getSourceRange();
78 }
79 else if (const CXXTempObjectRegion *TOR = dyn_cast<CXXTempObjectRegion>(R)) {
80 os << "stack memory associated with temporary object of type '"
81 << TOR->getValueType().getAsString() << '\'';
82 range = TOR->getExpr()->getSourceRange();
83 }
84 else {
85 llvm_unreachable("Invalid region in ReturnStackAddressChecker.");
86 }
87
88 return range;
89 }
90
EmitStackError(CheckerContext & C,const MemRegion * R,const Expr * RetE) const91 void StackAddrEscapeChecker::EmitStackError(CheckerContext &C, const MemRegion *R,
92 const Expr *RetE) const {
93 ExplodedNode *N = C.generateSink();
94
95 if (!N)
96 return;
97
98 if (!BT_returnstack)
99 BT_returnstack.reset(
100 new BuiltinBug("Return of address to stack-allocated memory"));
101
102 // Generate a report for this bug.
103 SmallString<512> buf;
104 llvm::raw_svector_ostream os(buf);
105 SourceRange range = GenName(os, R, C.getSourceManager());
106 os << " returned to caller";
107 BugReport *report = new BugReport(*BT_returnstack, os.str(), N);
108 report->addRange(RetE->getSourceRange());
109 if (range.isValid())
110 report->addRange(range);
111
112 C.EmitReport(report);
113 }
114
checkPreStmt(const ReturnStmt * RS,CheckerContext & C) const115 void StackAddrEscapeChecker::checkPreStmt(const ReturnStmt *RS,
116 CheckerContext &C) const {
117
118 const Expr *RetE = RS->getRetValue();
119 if (!RetE)
120 return;
121 RetE = RetE->IgnoreParens();
122
123 const LocationContext *LCtx = C.getLocationContext();
124 SVal V = C.getState()->getSVal(RetE, LCtx);
125 const MemRegion *R = V.getAsRegion();
126
127 if (!R)
128 return;
129
130 const StackSpaceRegion *SS =
131 dyn_cast_or_null<StackSpaceRegion>(R->getMemorySpace());
132
133 if (!SS)
134 return;
135
136 // Return stack memory in an ancestor stack frame is fine.
137 const StackFrameContext *CurFrame = LCtx->getCurrentStackFrame();
138 const StackFrameContext *MemFrame = SS->getStackFrame();
139 if (MemFrame != CurFrame)
140 return;
141
142 // Automatic reference counting automatically copies blocks.
143 if (C.getASTContext().getLangOpts().ObjCAutoRefCount &&
144 isa<BlockDataRegion>(R))
145 return;
146
147 // Returning a record by value is fine. (In this case, the returned
148 // expression will be a copy-constructor, possibly wrapped in an
149 // ExprWithCleanups node.)
150 if (const ExprWithCleanups *Cleanup = dyn_cast<ExprWithCleanups>(RetE))
151 RetE = Cleanup->getSubExpr();
152 if (isa<CXXConstructExpr>(RetE) && RetE->getType()->isRecordType())
153 return;
154
155 EmitStackError(C, R, RetE);
156 }
157
checkEndPath(CheckerContext & Ctx) const158 void StackAddrEscapeChecker::checkEndPath(CheckerContext &Ctx) const {
159 ProgramStateRef state = Ctx.getState();
160
161 // Iterate over all bindings to global variables and see if it contains
162 // a memory region in the stack space.
163 class CallBack : public StoreManager::BindingsHandler {
164 private:
165 CheckerContext &Ctx;
166 const StackFrameContext *CurSFC;
167 public:
168 SmallVector<std::pair<const MemRegion*, const MemRegion*>, 10> V;
169
170 CallBack(CheckerContext &CC) :
171 Ctx(CC),
172 CurSFC(CC.getLocationContext()->getCurrentStackFrame())
173 {}
174
175 bool HandleBinding(StoreManager &SMgr, Store store,
176 const MemRegion *region, SVal val) {
177
178 if (!isa<GlobalsSpaceRegion>(region->getMemorySpace()))
179 return true;
180
181 const MemRegion *vR = val.getAsRegion();
182 if (!vR)
183 return true;
184
185 // Under automated retain release, it is okay to assign a block
186 // directly to a global variable.
187 if (Ctx.getASTContext().getLangOpts().ObjCAutoRefCount &&
188 isa<BlockDataRegion>(vR))
189 return true;
190
191 if (const StackSpaceRegion *SSR =
192 dyn_cast<StackSpaceRegion>(vR->getMemorySpace())) {
193 // If the global variable holds a location in the current stack frame,
194 // record the binding to emit a warning.
195 if (SSR->getStackFrame() == CurSFC)
196 V.push_back(std::make_pair(region, vR));
197 }
198
199 return true;
200 }
201 };
202
203 CallBack cb(Ctx);
204 state->getStateManager().getStoreManager().iterBindings(state->getStore(),cb);
205
206 if (cb.V.empty())
207 return;
208
209 // Generate an error node.
210 ExplodedNode *N = Ctx.addTransition(state);
211 if (!N)
212 return;
213
214 if (!BT_stackleak)
215 BT_stackleak.reset(
216 new BuiltinBug("Stack address stored into global variable",
217 "Stack address was saved into a global variable. "
218 "This is dangerous because the address will become "
219 "invalid after returning from the function"));
220
221 for (unsigned i = 0, e = cb.V.size(); i != e; ++i) {
222 // Generate a report for this bug.
223 SmallString<512> buf;
224 llvm::raw_svector_ostream os(buf);
225 SourceRange range = GenName(os, cb.V[i].second,
226 Ctx.getSourceManager());
227 os << " is still referred to by the global variable '";
228 const VarRegion *VR = cast<VarRegion>(cb.V[i].first->getBaseRegion());
229 os << *VR->getDecl()
230 << "' upon returning to the caller. This will be a dangling reference";
231 BugReport *report = new BugReport(*BT_stackleak, os.str(), N);
232 if (range.isValid())
233 report->addRange(range);
234
235 Ctx.EmitReport(report);
236 }
237 }
238
registerStackAddrEscapeChecker(CheckerManager & mgr)239 void ento::registerStackAddrEscapeChecker(CheckerManager &mgr) {
240 mgr.registerChecker<StackAddrEscapeChecker>();
241 }
242