[clang] [clang][analyzer] Improve StdLibraryFunctionsChecker 'readlink' modeling. (PR #71373)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-clang

@llvm/pr-subscribers-clang-static-analyzer-1

Author: Balázs Kéri (balazske)

<details>
<summary>Changes</summary>

The functions 'readlink' and 'readlinkat' do return 0 only if the 'bufsize' argument is 0.

---
Full diff: https://github.com/llvm/llvm-project/pull/71373.diff


2 Files Affected:

- (modified) clang/lib/StaticAnalyzer/Checkers/StdLibraryFunctionsChecker.cpp (+14-4) 
- (modified) clang/test/Analysis/std-c-library-functions-POSIX.c (+20) 


``````````diff
diff --git a/clang/lib/StaticAnalyzer/Checkers/StdLibraryFunctionsChecker.cpp b/clang/lib/StaticAnalyzer/Checkers/StdLibraryFunctionsChecker.cpp
index 13bb9cef5e490ed..54a41b8bd7843dd 100644
--- a/clang/lib/StaticAnalyzer/Checkers/StdLibraryFunctionsChecker.cpp
+++ b/clang/lib/StaticAnalyzer/Checkers/StdLibraryFunctionsChecker.cpp
@@ -2865,9 +2865,14 @@ void StdLibraryFunctionsChecker::initFunctionSummaries(
         Signature(ArgTypes{ConstCharPtrRestrictTy, CharPtrRestrictTy, SizeTy},
                   RetType{Ssize_tTy}),
         Summary(NoEvalCall)
-            .Case({ReturnValueCondition(LessThanOrEq, ArgNo(2)),
-                   ReturnValueCondition(WithinRange, Range(0, Ssize_tMax))},
+            .Case({ArgumentCondition(2, WithinRange, Range(1, IntMax)),
+                   ReturnValueCondition(LessThanOrEq, ArgNo(2)),
+                   ReturnValueCondition(WithinRange, Range(1, Ssize_tMax))},
                   ErrnoMustNotBeChecked, GenericSuccessMsg)
+            .Case({ArgumentCondition(2, WithinRange, SingleValue(0)),
+                   ReturnValueCondition(WithinRange, SingleValue(0))},
+                  ErrnoMustNotBeChecked,
+                  "Assuming that argument 'bufsize' is 0")
             .Case(ReturnsMinusOne, ErrnoNEZeroIrrelevant, GenericFailureMsg)
             .ArgConstraint(NotNull(ArgNo(0)))
             .ArgConstraint(NotNull(ArgNo(1)))
@@ -2884,9 +2889,14 @@ void StdLibraryFunctionsChecker::initFunctionSummaries(
             ArgTypes{IntTy, ConstCharPtrRestrictTy, CharPtrRestrictTy, SizeTy},
             RetType{Ssize_tTy}),
         Summary(NoEvalCall)
-            .Case({ReturnValueCondition(LessThanOrEq, ArgNo(3)),
-                   ReturnValueCondition(WithinRange, Range(0, Ssize_tMax))},
+            .Case({ArgumentCondition(3, WithinRange, Range(1, IntMax)),
+                   ReturnValueCondition(LessThanOrEq, ArgNo(3)),
+                   ReturnValueCondition(WithinRange, Range(1, Ssize_tMax))},
                   ErrnoMustNotBeChecked, GenericSuccessMsg)
+            .Case({ArgumentCondition(3, WithinRange, SingleValue(0)),
+                   ReturnValueCondition(WithinRange, SingleValue(0))},
+                  ErrnoMustNotBeChecked,
+                  "Assuming that argument 'bufsize' is 0")
             .Case(ReturnsMinusOne, ErrnoNEZeroIrrelevant, GenericFailureMsg)
             .ArgConstraint(ValidFileDescriptorOrAtFdcwd(ArgNo(0)))
             .ArgConstraint(NotNull(ArgNo(1)))
diff --git a/clang/test/Analysis/std-c-library-functions-POSIX.c b/clang/test/Analysis/std-c-library-functions-POSIX.c
index 84ce0f21e569fb5..daa4d904c3ac5ed 100644
--- a/clang/test/Analysis/std-c-library-functions-POSIX.c
+++ b/clang/test/Analysis/std-c-library-functions-POSIX.c
@@ -205,3 +205,23 @@ void test_sendmsg(int sockfd, const struct msghdr *msg, int flags) {
   ssize_t Ret = sendmsg(sockfd, msg, flags);
   clang_analyzer_eval(Ret != 0); // expected-warning{{TRUE}}
 }
+
+void test_readlink_bufsize_zero(char *Buf, size_t Bufsize) {
+  ssize_t Ret = readlink("path", Buf, Bufsize);
+  if (Ret == 0)
+    clang_analyzer_eval(Bufsize == 0); // expected-warning{{TRUE}}
+  else if (Ret > 0)
+    clang_analyzer_eval(Bufsize == 0); // expected-warning{{FALSE}}
+  else
+    clang_analyzer_eval(Bufsize == 0); // expected-warning{{UNKNOWN}}
+}
+
+void test_readlinkat_bufsize_zero(int fd, char *Buf, size_t Bufsize) {
+  ssize_t Ret = readlinkat(fd, "path", Buf, Bufsize);
+  if (Ret == 0)
+    clang_analyzer_eval(Bufsize == 0); // expected-warning{{TRUE}}
+  else if (Ret > 0)
+    clang_analyzer_eval(Bufsize == 0); // expected-warning{{FALSE}}
+  else
+    clang_analyzer_eval(Bufsize == 0); // expected-warning{{UNKNOWN}}
+}

``````````

</details>


https://github.com/llvm/llvm-project/pull/71373