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

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

3 files changed, 43 insertions, 4 deletions

diff --git a/clang/lib/StaticAnalyzer/Checkers/StdLibraryFunctionsChecker.cpp b/clang/lib/StaticAnalyzer/Checkers/StdLibraryFunctionsChecker.cpp
index 13bb9ce..54a41b8 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 84ce0f21..daa4d90 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}}
+}
diff --git a/clang/test/Analysis/std-c-library-functions-path-notes.c b/clang/test/Analysis/std-c-library-functions-path-notes.c
index d095748..4df00fe 100644
--- a/clang/test/Analysis/std-c-library-functions-path-notes.c
+++ b/clang/test/Analysis/std-c-library-functions-path-notes.c
@@ -80,3 +80,12 @@ int test_fileno_arg_note(FILE *f1) {
   // expected-note{{The 1st argument to 'dup' is < 0 but should be >= 0}} \
   // expected-note{{Assuming that 'fileno' fails}}
 }
+
+int test_readlink_bufsize_zero(char *Buf, size_t Bufsize) {
+  ssize_t Ret = readlink("path", Buf, Bufsize); // \
+  // expected-note{{Assuming that argument 'bufsize' is 0}} \
+  // expected-note{{'Ret' initialized here}}
+  return 1 / Ret; // \
+  // expected-warning{{Division by zero}} \
+  // expected-note{{Division by zero}}
+}