[analyzer] CStringSyntaxChecks: Fix an off-by-one error in the strlca…

…t() check.

oth strlcat and strlcpy cut off their safe bound for the argument value
at sizeof(destination). There's no need to subtract 1 in only one
of these cases.

Differential Revision: https://reviews.llvm.org/D57981

rdar://problem/47873212

llvm-svn: 353583

clang/lib/StaticAnalyzer/Checkers/CStringSyntaxChecker.cpp

@@ -153,8 +153,6 @@ bool WalkAST::containsBadStrncatPattern(const CallExpr *CE) {
 bool WalkAST::containsBadStrlcpyStrlcatPattern(const CallExpr *CE) {
   if (CE->getNumArgs() != 3)
     return false;
-  const FunctionDecl *FD = CE->getDirectCallee();
-  bool Append = CheckerContext::isCLibraryFunction(FD, "strlcat");
   const Expr *DstArg = CE->getArg(0);
   const Expr *LenArg = CE->getArg(2);
 
@@ -194,13 +192,8 @@ bool WalkAST::containsBadStrlcpyStrlcatPattern(const CallExpr *CE) {
         ASTContext &C = BR.getContext();
         uint64_t BufferLen = C.getTypeSize(Buffer) / 8;
         auto RemainingBufferLen = BufferLen - DstOff;
-        if (Append) {
-          if (RemainingBufferLen <= ILRawVal)
-            return true;
-        } else {
-          if (RemainingBufferLen < ILRawVal)
-            return true;
-        }
+        if (RemainingBufferLen < ILRawVal)
+          return true;
       }
     }
   }

clang/test/Analysis/cstring-syntax.c

@@ -33,6 +33,7 @@ void testStrlcpy(const char *src) {
   strlcpy(dest, src, ulen);
   strlcpy(dest + 5, src, 5);
   strlcpy(dest + 5, src, 10); // expected-warning {{The third argument allows to potentially copy more bytes than it should. Replace with the value sizeof(<destination buffer>) or lower}}
+  strlcpy(dest, "aaaaaaaaaaaaaaa", 10); // no-warning
 }
 
 void testStrlcat(const char *src) {
@@ -51,4 +52,5 @@ void testStrlcat(const char *src) {
   strlcat(dest, src, ulen);
   strlcpy(dest, src, 5);
   strlcat(dest + 5, src, badlen); // expected-warning {{The third argument allows to potentially copy more bytes than it should. Replace with the value sizeof(<destination buffer>) or lower}}
+  strlcat(dest, "aaaaaaaaaaaaaaa", 10); // no-warning
 }