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

[Balázs Kéri via cfe-commits]

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

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

>From 653aeb7f5b0d0f200b3f706bad770a9be643669c Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Bal=C3=A1zs=20K=C3=A9ri?= <balazs.keri at ericsson.com>
Date: Fri, 3 Nov 2023 09:48:18 +0100
Subject: [PATCH] [clang][analyzer] Improve StdLibraryFunctionsChecker
 'readlink' modeling.

The functions 'readlink' and 'readlinkat' do return 0 only if the
'bufsize' argument is 0.
---
 .../Checkers/StdLibraryFunctionsChecker.cpp   | 18 +++++++++++++----
 .../Analysis/std-c-library-functions-POSIX.c  | 20 +++++++++++++++++++
 2 files changed, 34 insertions(+), 4 deletions(-)

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}}
+}