1 //==- CheckSecuritySyntaxOnly.cpp - Basic security checks --------*- 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 a set of flow-insensitive security checks.
11 //
12 //===----------------------------------------------------------------------===//
13
14 #include "ClangSACheckers.h"
15 #include "clang/StaticAnalyzer/Core/Checker.h"
16 #include "clang/StaticAnalyzer/Core/BugReporter/BugReporter.h"
17 #include "clang/Basic/TargetInfo.h"
18 #include "clang/AST/StmtVisitor.h"
19 #include "llvm/Support/raw_ostream.h"
20 #include "llvm/ADT/StringSwitch.h"
21
22 using namespace clang;
23 using namespace ento;
24
isArc4RandomAvailable(const ASTContext & Ctx)25 static bool isArc4RandomAvailable(const ASTContext &Ctx) {
26 const llvm::Triple &T = Ctx.Target.getTriple();
27 return T.getVendor() == llvm::Triple::Apple ||
28 T.getOS() == llvm::Triple::FreeBSD ||
29 T.getOS() == llvm::Triple::NetBSD ||
30 T.getOS() == llvm::Triple::OpenBSD ||
31 T.getOS() == llvm::Triple::DragonFly;
32 }
33
34 namespace {
35 class WalkAST : public StmtVisitor<WalkAST> {
36 BugReporter &BR;
37 enum { num_setids = 6 };
38 IdentifierInfo *II_setid[num_setids];
39
40 const bool CheckRand;
41
42 public:
WalkAST(BugReporter & br)43 WalkAST(BugReporter &br) : BR(br), II_setid(),
44 CheckRand(isArc4RandomAvailable(BR.getContext())) {}
45
46 // Statement visitor methods.
47 void VisitCallExpr(CallExpr *CE);
48 void VisitForStmt(ForStmt *S);
49 void VisitCompoundStmt (CompoundStmt *S);
VisitStmt(Stmt * S)50 void VisitStmt(Stmt *S) { VisitChildren(S); }
51
52 void VisitChildren(Stmt *S);
53
54 // Helpers.
55 IdentifierInfo *getIdentifier(IdentifierInfo *& II, const char *str);
56 bool checkCall_strCommon(const CallExpr *CE, const FunctionDecl *FD);
57
58 typedef void (WalkAST::*FnCheck)(const CallExpr *,
59 const FunctionDecl *);
60
61 // Checker-specific methods.
62 void checkLoopConditionForFloat(const ForStmt *FS);
63 void checkCall_gets(const CallExpr *CE, const FunctionDecl *FD);
64 void checkCall_getpw(const CallExpr *CE, const FunctionDecl *FD);
65 void checkCall_mktemp(const CallExpr *CE, const FunctionDecl *FD);
66 void checkCall_strcpy(const CallExpr *CE, const FunctionDecl *FD);
67 void checkCall_strcat(const CallExpr *CE, const FunctionDecl *FD);
68 void checkCall_rand(const CallExpr *CE, const FunctionDecl *FD);
69 void checkCall_random(const CallExpr *CE, const FunctionDecl *FD);
70 void checkUncheckedReturnValue(CallExpr *CE);
71 };
72 } // end anonymous namespace
73
74 //===----------------------------------------------------------------------===//
75 // Helper methods.
76 //===----------------------------------------------------------------------===//
77
getIdentifier(IdentifierInfo * & II,const char * str)78 IdentifierInfo *WalkAST::getIdentifier(IdentifierInfo *& II, const char *str) {
79 if (!II)
80 II = &BR.getContext().Idents.get(str);
81
82 return II;
83 }
84
85 //===----------------------------------------------------------------------===//
86 // AST walking.
87 //===----------------------------------------------------------------------===//
88
VisitChildren(Stmt * S)89 void WalkAST::VisitChildren(Stmt *S) {
90 for (Stmt::child_iterator I = S->child_begin(), E = S->child_end(); I!=E; ++I)
91 if (Stmt *child = *I)
92 Visit(child);
93 }
94
VisitCallExpr(CallExpr * CE)95 void WalkAST::VisitCallExpr(CallExpr *CE) {
96 // Get the callee.
97 const FunctionDecl *FD = CE->getDirectCallee();
98
99 if (!FD)
100 return;
101
102 // Get the name of the callee. If it's a builtin, strip off the prefix.
103 IdentifierInfo *II = FD->getIdentifier();
104 if (!II) // if no identifier, not a simple C function
105 return;
106 llvm::StringRef Name = II->getName();
107 if (Name.startswith("__builtin_"))
108 Name = Name.substr(10);
109
110 // Set the evaluation function by switching on the callee name.
111 FnCheck evalFunction = llvm::StringSwitch<FnCheck>(Name)
112 .Case("gets", &WalkAST::checkCall_gets)
113 .Case("getpw", &WalkAST::checkCall_getpw)
114 .Case("mktemp", &WalkAST::checkCall_mktemp)
115 .Cases("strcpy", "__strcpy_chk", &WalkAST::checkCall_strcpy)
116 .Cases("strcat", "__strcat_chk", &WalkAST::checkCall_strcat)
117 .Case("drand48", &WalkAST::checkCall_rand)
118 .Case("erand48", &WalkAST::checkCall_rand)
119 .Case("jrand48", &WalkAST::checkCall_rand)
120 .Case("lrand48", &WalkAST::checkCall_rand)
121 .Case("mrand48", &WalkAST::checkCall_rand)
122 .Case("nrand48", &WalkAST::checkCall_rand)
123 .Case("lcong48", &WalkAST::checkCall_rand)
124 .Case("rand", &WalkAST::checkCall_rand)
125 .Case("rand_r", &WalkAST::checkCall_rand)
126 .Case("random", &WalkAST::checkCall_random)
127 .Default(NULL);
128
129 // If the callee isn't defined, it is not of security concern.
130 // Check and evaluate the call.
131 if (evalFunction)
132 (this->*evalFunction)(CE, FD);
133
134 // Recurse and check children.
135 VisitChildren(CE);
136 }
137
VisitCompoundStmt(CompoundStmt * S)138 void WalkAST::VisitCompoundStmt(CompoundStmt *S) {
139 for (Stmt::child_iterator I = S->child_begin(), E = S->child_end(); I!=E; ++I)
140 if (Stmt *child = *I) {
141 if (CallExpr *CE = dyn_cast<CallExpr>(child))
142 checkUncheckedReturnValue(CE);
143 Visit(child);
144 }
145 }
146
VisitForStmt(ForStmt * FS)147 void WalkAST::VisitForStmt(ForStmt *FS) {
148 checkLoopConditionForFloat(FS);
149
150 // Recurse and check children.
151 VisitChildren(FS);
152 }
153
154 //===----------------------------------------------------------------------===//
155 // Check: floating poing variable used as loop counter.
156 // Originally: <rdar://problem/6336718>
157 // Implements: CERT security coding advisory FLP-30.
158 //===----------------------------------------------------------------------===//
159
160 static const DeclRefExpr*
getIncrementedVar(const Expr * expr,const VarDecl * x,const VarDecl * y)161 getIncrementedVar(const Expr *expr, const VarDecl *x, const VarDecl *y) {
162 expr = expr->IgnoreParenCasts();
163
164 if (const BinaryOperator *B = dyn_cast<BinaryOperator>(expr)) {
165 if (!(B->isAssignmentOp() || B->isCompoundAssignmentOp() ||
166 B->getOpcode() == BO_Comma))
167 return NULL;
168
169 if (const DeclRefExpr *lhs = getIncrementedVar(B->getLHS(), x, y))
170 return lhs;
171
172 if (const DeclRefExpr *rhs = getIncrementedVar(B->getRHS(), x, y))
173 return rhs;
174
175 return NULL;
176 }
177
178 if (const DeclRefExpr *DR = dyn_cast<DeclRefExpr>(expr)) {
179 const NamedDecl *ND = DR->getDecl();
180 return ND == x || ND == y ? DR : NULL;
181 }
182
183 if (const UnaryOperator *U = dyn_cast<UnaryOperator>(expr))
184 return U->isIncrementDecrementOp()
185 ? getIncrementedVar(U->getSubExpr(), x, y) : NULL;
186
187 return NULL;
188 }
189
190 /// CheckLoopConditionForFloat - This check looks for 'for' statements that
191 /// use a floating point variable as a loop counter.
192 /// CERT: FLP30-C, FLP30-CPP.
193 ///
checkLoopConditionForFloat(const ForStmt * FS)194 void WalkAST::checkLoopConditionForFloat(const ForStmt *FS) {
195 // Does the loop have a condition?
196 const Expr *condition = FS->getCond();
197
198 if (!condition)
199 return;
200
201 // Does the loop have an increment?
202 const Expr *increment = FS->getInc();
203
204 if (!increment)
205 return;
206
207 // Strip away '()' and casts.
208 condition = condition->IgnoreParenCasts();
209 increment = increment->IgnoreParenCasts();
210
211 // Is the loop condition a comparison?
212 const BinaryOperator *B = dyn_cast<BinaryOperator>(condition);
213
214 if (!B)
215 return;
216
217 // Is this a comparison?
218 if (!(B->isRelationalOp() || B->isEqualityOp()))
219 return;
220
221 // Are we comparing variables?
222 const DeclRefExpr *drLHS =
223 dyn_cast<DeclRefExpr>(B->getLHS()->IgnoreParenLValueCasts());
224 const DeclRefExpr *drRHS =
225 dyn_cast<DeclRefExpr>(B->getRHS()->IgnoreParenLValueCasts());
226
227 // Does at least one of the variables have a floating point type?
228 drLHS = drLHS && drLHS->getType()->isRealFloatingType() ? drLHS : NULL;
229 drRHS = drRHS && drRHS->getType()->isRealFloatingType() ? drRHS : NULL;
230
231 if (!drLHS && !drRHS)
232 return;
233
234 const VarDecl *vdLHS = drLHS ? dyn_cast<VarDecl>(drLHS->getDecl()) : NULL;
235 const VarDecl *vdRHS = drRHS ? dyn_cast<VarDecl>(drRHS->getDecl()) : NULL;
236
237 if (!vdLHS && !vdRHS)
238 return;
239
240 // Does either variable appear in increment?
241 const DeclRefExpr *drInc = getIncrementedVar(increment, vdLHS, vdRHS);
242
243 if (!drInc)
244 return;
245
246 // Emit the error. First figure out which DeclRefExpr in the condition
247 // referenced the compared variable.
248 const DeclRefExpr *drCond = vdLHS == drInc->getDecl() ? drLHS : drRHS;
249
250 llvm::SmallVector<SourceRange, 2> ranges;
251 llvm::SmallString<256> sbuf;
252 llvm::raw_svector_ostream os(sbuf);
253
254 os << "Variable '" << drCond->getDecl()->getName()
255 << "' with floating point type '" << drCond->getType().getAsString()
256 << "' should not be used as a loop counter";
257
258 ranges.push_back(drCond->getSourceRange());
259 ranges.push_back(drInc->getSourceRange());
260
261 const char *bugType = "Floating point variable used as loop counter";
262 BR.EmitBasicReport(bugType, "Security", os.str(),
263 FS->getLocStart(), ranges.data(), ranges.size());
264 }
265
266 //===----------------------------------------------------------------------===//
267 // Check: Any use of 'gets' is insecure.
268 // Originally: <rdar://problem/6335715>
269 // Implements (part of): 300-BSI (buildsecurityin.us-cert.gov)
270 // CWE-242: Use of Inherently Dangerous Function
271 //===----------------------------------------------------------------------===//
272
checkCall_gets(const CallExpr * CE,const FunctionDecl * FD)273 void WalkAST::checkCall_gets(const CallExpr *CE, const FunctionDecl *FD) {
274 const FunctionProtoType *FPT
275 = dyn_cast<FunctionProtoType>(FD->getType().IgnoreParens());
276 if (!FPT)
277 return;
278
279 // Verify that the function takes a single argument.
280 if (FPT->getNumArgs() != 1)
281 return;
282
283 // Is the argument a 'char*'?
284 const PointerType *PT = dyn_cast<PointerType>(FPT->getArgType(0));
285 if (!PT)
286 return;
287
288 if (PT->getPointeeType().getUnqualifiedType() != BR.getContext().CharTy)
289 return;
290
291 // Issue a warning.
292 SourceRange R = CE->getCallee()->getSourceRange();
293 BR.EmitBasicReport("Potential buffer overflow in call to 'gets'",
294 "Security",
295 "Call to function 'gets' is extremely insecure as it can "
296 "always result in a buffer overflow",
297 CE->getLocStart(), &R, 1);
298 }
299
300 //===----------------------------------------------------------------------===//
301 // Check: Any use of 'getpwd' is insecure.
302 // CWE-477: Use of Obsolete Functions
303 //===----------------------------------------------------------------------===//
304
checkCall_getpw(const CallExpr * CE,const FunctionDecl * FD)305 void WalkAST::checkCall_getpw(const CallExpr *CE, const FunctionDecl *FD) {
306 const FunctionProtoType *FPT
307 = dyn_cast<FunctionProtoType>(FD->getType().IgnoreParens());
308 if (!FPT)
309 return;
310
311 // Verify that the function takes two arguments.
312 if (FPT->getNumArgs() != 2)
313 return;
314
315 // Verify the first argument type is integer.
316 if (!FPT->getArgType(0)->isIntegerType())
317 return;
318
319 // Verify the second argument type is char*.
320 const PointerType *PT = dyn_cast<PointerType>(FPT->getArgType(1));
321 if (!PT)
322 return;
323
324 if (PT->getPointeeType().getUnqualifiedType() != BR.getContext().CharTy)
325 return;
326
327 // Issue a warning.
328 SourceRange R = CE->getCallee()->getSourceRange();
329 BR.EmitBasicReport("Potential buffer overflow in call to 'getpw'",
330 "Security",
331 "The getpw() function is dangerous as it may overflow the "
332 "provided buffer. It is obsoleted by getpwuid().",
333 CE->getLocStart(), &R, 1);
334 }
335
336 //===----------------------------------------------------------------------===//
337 // Check: Any use of 'mktemp' is insecure.It is obsoleted by mkstemp().
338 // CWE-377: Insecure Temporary File
339 //===----------------------------------------------------------------------===//
340
checkCall_mktemp(const CallExpr * CE,const FunctionDecl * FD)341 void WalkAST::checkCall_mktemp(const CallExpr *CE, const FunctionDecl *FD) {
342 const FunctionProtoType *FPT
343 = dyn_cast<FunctionProtoType>(FD->getType().IgnoreParens());
344 if(!FPT)
345 return;
346
347 // Verify that the function takes a single argument.
348 if (FPT->getNumArgs() != 1)
349 return;
350
351 // Verify that the argument is Pointer Type.
352 const PointerType *PT = dyn_cast<PointerType>(FPT->getArgType(0));
353 if (!PT)
354 return;
355
356 // Verify that the argument is a 'char*'.
357 if (PT->getPointeeType().getUnqualifiedType() != BR.getContext().CharTy)
358 return;
359
360 // Issue a waring.
361 SourceRange R = CE->getCallee()->getSourceRange();
362 BR.EmitBasicReport("Potential insecure temporary file in call 'mktemp'",
363 "Security",
364 "Call to function 'mktemp' is insecure as it always "
365 "creates or uses insecure temporary file. Use 'mkstemp' instead",
366 CE->getLocStart(), &R, 1);
367 }
368
369 //===----------------------------------------------------------------------===//
370 // Check: Any use of 'strcpy' is insecure.
371 //
372 // CWE-119: Improper Restriction of Operations within
373 // the Bounds of a Memory Buffer
374 //===----------------------------------------------------------------------===//
checkCall_strcpy(const CallExpr * CE,const FunctionDecl * FD)375 void WalkAST::checkCall_strcpy(const CallExpr *CE, const FunctionDecl *FD) {
376 if (!checkCall_strCommon(CE, FD))
377 return;
378
379 // Issue a warning.
380 SourceRange R = CE->getCallee()->getSourceRange();
381 BR.EmitBasicReport("Potential insecure memory buffer bounds restriction in "
382 "call 'strcpy'",
383 "Security",
384 "Call to function 'strcpy' is insecure as it does not "
385 "provide bounding of the memory buffer. Replace "
386 "unbounded copy functions with analogous functions that "
387 "support length arguments such as 'strncpy'. CWE-119.",
388 CE->getLocStart(), &R, 1);
389 }
390
391 //===----------------------------------------------------------------------===//
392 // Check: Any use of 'strcat' is insecure.
393 //
394 // CWE-119: Improper Restriction of Operations within
395 // the Bounds of a Memory Buffer
396 //===----------------------------------------------------------------------===//
checkCall_strcat(const CallExpr * CE,const FunctionDecl * FD)397 void WalkAST::checkCall_strcat(const CallExpr *CE, const FunctionDecl *FD) {
398 if (!checkCall_strCommon(CE, FD))
399 return;
400
401 // Issue a warning.
402 SourceRange R = CE->getCallee()->getSourceRange();
403 BR.EmitBasicReport("Potential insecure memory buffer bounds restriction in "
404 "call 'strcat'",
405 "Security",
406 "Call to function 'strcat' is insecure as it does not "
407 "provide bounding of the memory buffer. Replace "
408 "unbounded copy functions with analogous functions that "
409 "support length arguments such as 'strncat'. CWE-119.",
410 CE->getLocStart(), &R, 1);
411 }
412
413 //===----------------------------------------------------------------------===//
414 // Common check for str* functions with no bounds parameters.
415 //===----------------------------------------------------------------------===//
checkCall_strCommon(const CallExpr * CE,const FunctionDecl * FD)416 bool WalkAST::checkCall_strCommon(const CallExpr *CE, const FunctionDecl *FD) {
417 const FunctionProtoType *FPT
418 = dyn_cast<FunctionProtoType>(FD->getType().IgnoreParens());
419 if (!FPT)
420 return false;
421
422 // Verify the function takes two arguments, three in the _chk version.
423 int numArgs = FPT->getNumArgs();
424 if (numArgs != 2 && numArgs != 3)
425 return false;
426
427 // Verify the type for both arguments.
428 for (int i = 0; i < 2; i++) {
429 // Verify that the arguments are pointers.
430 const PointerType *PT = dyn_cast<PointerType>(FPT->getArgType(i));
431 if (!PT)
432 return false;
433
434 // Verify that the argument is a 'char*'.
435 if (PT->getPointeeType().getUnqualifiedType() != BR.getContext().CharTy)
436 return false;
437 }
438
439 return true;
440 }
441
442 //===----------------------------------------------------------------------===//
443 // Check: Linear congruent random number generators should not be used
444 // Originally: <rdar://problem/63371000>
445 // CWE-338: Use of cryptographically weak prng
446 //===----------------------------------------------------------------------===//
447
checkCall_rand(const CallExpr * CE,const FunctionDecl * FD)448 void WalkAST::checkCall_rand(const CallExpr *CE, const FunctionDecl *FD) {
449 if (!CheckRand)
450 return;
451
452 const FunctionProtoType *FTP
453 = dyn_cast<FunctionProtoType>(FD->getType().IgnoreParens());
454 if (!FTP)
455 return;
456
457 if (FTP->getNumArgs() == 1) {
458 // Is the argument an 'unsigned short *'?
459 // (Actually any integer type is allowed.)
460 const PointerType *PT = dyn_cast<PointerType>(FTP->getArgType(0));
461 if (!PT)
462 return;
463
464 if (! PT->getPointeeType()->isIntegerType())
465 return;
466 }
467 else if (FTP->getNumArgs() != 0)
468 return;
469
470 // Issue a warning.
471 llvm::SmallString<256> buf1;
472 llvm::raw_svector_ostream os1(buf1);
473 os1 << '\'' << FD << "' is a poor random number generator";
474
475 llvm::SmallString<256> buf2;
476 llvm::raw_svector_ostream os2(buf2);
477 os2 << "Function '" << FD
478 << "' is obsolete because it implements a poor random number generator."
479 << " Use 'arc4random' instead";
480
481 SourceRange R = CE->getCallee()->getSourceRange();
482 BR.EmitBasicReport(os1.str(), "Security", os2.str(),CE->getLocStart(), &R, 1);
483 }
484
485 //===----------------------------------------------------------------------===//
486 // Check: 'random' should not be used
487 // Originally: <rdar://problem/63371000>
488 //===----------------------------------------------------------------------===//
489
checkCall_random(const CallExpr * CE,const FunctionDecl * FD)490 void WalkAST::checkCall_random(const CallExpr *CE, const FunctionDecl *FD) {
491 if (!CheckRand)
492 return;
493
494 const FunctionProtoType *FTP
495 = dyn_cast<FunctionProtoType>(FD->getType().IgnoreParens());
496 if (!FTP)
497 return;
498
499 // Verify that the function takes no argument.
500 if (FTP->getNumArgs() != 0)
501 return;
502
503 // Issue a warning.
504 SourceRange R = CE->getCallee()->getSourceRange();
505 BR.EmitBasicReport("'random' is not a secure random number generator",
506 "Security",
507 "The 'random' function produces a sequence of values that "
508 "an adversary may be able to predict. Use 'arc4random' "
509 "instead", CE->getLocStart(), &R, 1);
510 }
511
512 //===----------------------------------------------------------------------===//
513 // Check: Should check whether privileges are dropped successfully.
514 // Originally: <rdar://problem/6337132>
515 //===----------------------------------------------------------------------===//
516
checkUncheckedReturnValue(CallExpr * CE)517 void WalkAST::checkUncheckedReturnValue(CallExpr *CE) {
518 const FunctionDecl *FD = CE->getDirectCallee();
519 if (!FD)
520 return;
521
522 if (II_setid[0] == NULL) {
523 static const char * const identifiers[num_setids] = {
524 "setuid", "setgid", "seteuid", "setegid",
525 "setreuid", "setregid"
526 };
527
528 for (size_t i = 0; i < num_setids; i++)
529 II_setid[i] = &BR.getContext().Idents.get(identifiers[i]);
530 }
531
532 const IdentifierInfo *id = FD->getIdentifier();
533 size_t identifierid;
534
535 for (identifierid = 0; identifierid < num_setids; identifierid++)
536 if (id == II_setid[identifierid])
537 break;
538
539 if (identifierid >= num_setids)
540 return;
541
542 const FunctionProtoType *FTP
543 = dyn_cast<FunctionProtoType>(FD->getType().IgnoreParens());
544 if (!FTP)
545 return;
546
547 // Verify that the function takes one or two arguments (depending on
548 // the function).
549 if (FTP->getNumArgs() != (identifierid < 4 ? 1 : 2))
550 return;
551
552 // The arguments must be integers.
553 for (unsigned i = 0; i < FTP->getNumArgs(); i++)
554 if (! FTP->getArgType(i)->isIntegerType())
555 return;
556
557 // Issue a warning.
558 llvm::SmallString<256> buf1;
559 llvm::raw_svector_ostream os1(buf1);
560 os1 << "Return value is not checked in call to '" << FD << '\'';
561
562 llvm::SmallString<256> buf2;
563 llvm::raw_svector_ostream os2(buf2);
564 os2 << "The return value from the call to '" << FD
565 << "' is not checked. If an error occurs in '" << FD
566 << "', the following code may execute with unexpected privileges";
567
568 SourceRange R = CE->getCallee()->getSourceRange();
569 BR.EmitBasicReport(os1.str(), "Security", os2.str(),CE->getLocStart(), &R, 1);
570 }
571
572 //===----------------------------------------------------------------------===//
573 // SecuritySyntaxChecker
574 //===----------------------------------------------------------------------===//
575
576 namespace {
577 class SecuritySyntaxChecker : public Checker<check::ASTCodeBody> {
578 public:
checkASTCodeBody(const Decl * D,AnalysisManager & mgr,BugReporter & BR) const579 void checkASTCodeBody(const Decl *D, AnalysisManager& mgr,
580 BugReporter &BR) const {
581 WalkAST walker(BR);
582 walker.Visit(D->getBody());
583 }
584 };
585 }
586
registerSecuritySyntaxChecker(CheckerManager & mgr)587 void ento::registerSecuritySyntaxChecker(CheckerManager &mgr) {
588 mgr.registerChecker<SecuritySyntaxChecker>();
589 }
590