[analyzer] CStringChecker: fix crash in CheckOverlap when arguments are not pointers

[guillem-bartrina-sonarsource]

https://github.com/llvm/llvm-project/blob/main/clang/lib/StaticAnalyzer/Checkers/CStringChecker.cpp#L675-L678 mistakenly assumes that target expressions are of pointer type. CheckOverlap has multiple call sites, most of which do not verify this assumption. Therefore, the simplest solution is to verify it just before that point.

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[llvmbot]

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

@llvm/pr-subscribers-clang

Author: None (guillem-bartrina-sonarsource)

Changes

https://github.com/llvm/llvm-project/blob/main/clang/lib/StaticAnalyzer/Checkers/CStringChecker.cpp#L675-L678 mistakenly assumes that target expressions are of pointer type. CheckOverlap has multiple call sites, most of which do not verify this assumption. Therefore, the simplest solution is to verify it just before that point.

---

Full diff: https://github.com/llvm/llvm-project/pull/160511.diff

2 Files Affected:

• (modified) clang/lib/StaticAnalyzer/Checkers/CStringChecker.cpp (+4)
• (modified) clang/test/Analysis/buffer-overlap.c (+16)

diff --git a/clang/lib/StaticAnalyzer/Checkers/CStringChecker.cpp b/clang/lib/StaticAnalyzer/Checkers/CStringChecker.cpp
index 36f316df0c3ff..0ae784c000f60 100644
--- a/clang/lib/StaticAnalyzer/Checkers/CStringChecker.cpp
+++ b/clang/lib/StaticAnalyzer/Checkers/CStringChecker.cpp
@@ -672,6 +672,10 @@ ProgramStateRef CStringChecker::CheckOverlap(CheckerContext &C,
 
   ProgramStateRef stateTrue, stateFalse;
 
+  if (!First.Expression->getType()->isAnyPointerType() ||
+      !Second.Expression->getType()->isAnyPointerType())
+    return state;
+
   // Assume different address spaces cannot overlap.
   if (First.Expression->getType()->getPointeeType().getAddressSpace() !=
       Second.Expression->getType()->getPointeeType().getAddressSpace())
diff --git a/clang/test/Analysis/buffer-overlap.c b/clang/test/Analysis/buffer-overlap.c
index 8414a764541e2..f3bd49b8b9ca0 100644
--- a/clang/test/Analysis/buffer-overlap.c
+++ b/clang/test/Analysis/buffer-overlap.c
@@ -96,3 +96,19 @@ void test_snprintf6() {
   char b[4] = {0};
   snprintf(a, sizeof(a), "%s", b); // no-warning
 }
+
+
+void memcpy(int dst, int src, size_t size); // expected-warning{{incompatible redeclaration of library function 'memcpy'}} expected-note{{'memcpy' is a builtin with type 'void *(void *, const void *, __size_t)' (aka 'void *(void *, const void *, unsigned long)')}}
+void test_memcpy_proxy() {
+  memcpy(42, 42, 42);
+}
+
+void strcpy(int dst, char *src); // expected-warning{{incompatible redeclaration of library function 'strcpy'}} expected-note{{'strcpy' is a builtin with type 'char *(char *, const char *)'}}
+void test_strcpy_proxy() {
+  strcpy(42, (char *)42);
+}
+
+void strxfrm(int dst, char *src, size_t size); // expected-warning{{incompatible redeclaration of library function 'strxfrm'}} expected-note{{'strxfrm' is a builtin with type '__size_t (char *, const char *, __size_t)' (aka 'unsigned long (char *, const char *, unsigned long)')}}
+void test_strxfrm_proxy() {
+  strxfrm(42, (char *)42, 42);
+}

[NagyDonat]

Thanks for the commit, crash fixes are always welcome!

I added two very minor stylistic suggestion in inline comments, but the commit is also acceptable in its current form.

Moreover, in the commit message you write that "CheckOverlap has multiple call sites, most of which do not verify this assumption." which implies that some call sites did verify this assumption. Now that CheckOverlap does this verification, are there any call sites where the verification logic is made completely redundant by your change?

[steakhal]

[...] are there any call sites where the verification logic is made completely redundant by your change?

+1

Could we have a test passing other esoteric things as pointers, like the address of a label, a function pointer cast to a char pointer?

[guillem-bartrina-sonarsource]

Thanks @NagyDonat for the suggestions! I've applied both of them in 7b31427. I took the liberty of separating the test case into another file because it didn't fit well in the previous one, which had several // RUN commands for different flavors of the sprintf functions

Now that CheckOverlap does this verification, are there any call sites where the verification logic is made completely redundant by your change?

There are no call sites that verify all assumptions. Only https://github.com/llvm/llvm-project/blob/main/clang/lib/StaticAnalyzer/Checkers/CStringChecker.cpp#L2725-L2737 verified some of them, and that was incidental. In short: no, there is no redundant verification logic.

I also added a more esoteric test case, as suggested by @steakhal in aabc2f7. LMKWYT.

[NagyDonat]

LGTM, thanks for the updates!

One more minor remark is that perhaps buffer-overlap-nonstandard-decls.c would be a more descriptive name than buffer-overlap-alt.c.

[NagyDonat]

Still LGTM.

I'm happy to help with merging if you need it.

[guillem-bartrina-sonarsource]

I'm happy to help with merging if you need it.

I should be able to merge it after updating the branch, right? If not, feel free to merge it yourself if you can.

Sorry for the noise.

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