[PATCH] D19691: [asan] Assert in __sanitizer_ptr_{sub, cmp} if one of the pointers was freed.

[Filipe Cabecinhas via llvm-commits]

filcab created this revision.
filcab added reviewers: samsonov, kcc, rsmith, regehr.
filcab added a subscriber: llvm-commits.
Herald added a subscriber: kubabrecka.

This (partially) implements the check mentioned at
http://kristerw.blogspot.co.uk/2016/04/dangling-pointers-and-undefined-behavior.html
(via John Regehr)

Quoting:
"That the behavior is undefined follows from C11 6.2.4 "Storage
durations of objects"
  The lifetime of an object is the portion of program execution during
  which storage is guaranteed to be reserved for it. An object exists, has
  a constant address, and retains its last-stored value throughout its
  lifetime. If an object is referred to outside of its lifetime, the
  behavior is undefined. The value of a pointer becomes indeterminate when
  the object it points to (or just past) reaches the end of its lifetime.
and 7.22.3 "Memory management functions" that says that free ends the
lifetime of objects
  The lifetime of an allocated object extends from the allocation until
  the deallocation.
"

We can probably implement this for stack variables too, but I think this
is a good start to see if there's interest in this check.
We can also hide this behind a flag, too.

http://reviews.llvm.org/D19691

Files:
  lib/asan/asan_allocator.cc
  lib/asan/asan_allocator.h
  lib/asan/asan_report.cc
  test/asan/TestCases/invalid-pointer-pairs.cc

Index: test/asan/TestCases/invalid-pointer-pairs.cc
===================================================================
--- /dev/null
+++ test/asan/TestCases/invalid-pointer-pairs.cc
@@ -0,0 +1,22 @@
+// RUN: %clangxx_asan -O0 %s -o %t -mllvm -asan-detect-invalid-pointer-pair
+
+// RUN: %env_asan_opts=detect_invalid_pointer_pairs=true not %run %t 2>&1 | FileCheck %s
+
+#include <assert.h>
+#include <stdlib.h>
+
+int main(int argc, char **argv) {
+  assert(argc >= 2);
+  char *p = (char*)malloc(42);
+  char *q = (char*)malloc(42);
+  switch (argv[1][0]) {
+    case 'g':
+      return p > q;
+    case 's':
+      return p - q;
+    case 'f':
+      char *p2 = p+20;
+      free(p);
+      return p == p2;
+  }
+}
Index: lib/asan/asan_report.cc
===================================================================
--- lib/asan/asan_report.cc
+++ lib/asan/asan_report.cc
@@ -1012,10 +1012,10 @@
   uptr a2 = reinterpret_cast<uptr>(p2);
   AsanChunkView chunk1 = FindHeapChunkByAddress(a1);
   AsanChunkView chunk2 = FindHeapChunkByAddress(a2);
-  bool valid1 = chunk1.IsValid();
-  bool valid2 = chunk2.IsValid();
-  if ((valid1 != valid2) || (valid1 && valid2 && !chunk1.Eq(chunk2))) {
-    GET_CALLER_PC_BP_SP;                                              \
+  bool valid1 = chunk1.IsAllocated();
+  bool valid2 = chunk2.IsAllocated();
+  if (!valid1 || !valid2 || !chunk1.Eq(chunk2)) {
+    GET_CALLER_PC_BP_SP;
     return ReportInvalidPointerPair(pc, bp, sp, a1, a2);
   }
 }
Index: lib/asan/asan_allocator.h
===================================================================
--- lib/asan/asan_allocator.h
+++ lib/asan/asan_allocator.h
@@ -49,11 +49,12 @@
 class AsanChunkView {
  public:
   explicit AsanChunkView(AsanChunk *chunk) : chunk_(chunk) {}
-  bool IsValid();   // Checks if AsanChunkView points to a valid allocated
-                    // or quarantined chunk.
-  uptr Beg();       // First byte of user memory.
-  uptr End();       // Last byte of user memory.
-  uptr UsedSize();  // Size requested by the user.
+  bool IsValid();        // Checks if AsanChunkView points to a valid allocated
+                         // or quarantined chunk.
+  bool IsAllocated();    // Checks if the memory is currently allocated.
+  uptr Beg();            // First byte of user memory.
+  uptr End();            // Last byte of user memory.
+  uptr UsedSize();       // Size requested by the user.
   uptr AllocTid();
   uptr FreeTid();
   bool Eq(const AsanChunkView &c) const { return chunk_ == c.chunk_; }
Index: lib/asan/asan_allocator.cc
===================================================================
--- lib/asan/asan_allocator.cc
+++ lib/asan/asan_allocator.cc
@@ -665,6 +665,9 @@
 bool AsanChunkView::IsValid() {
   return chunk_ && chunk_->chunk_state != CHUNK_AVAILABLE;
 }
+bool AsanChunkView::IsAllocated() {
+  return chunk_ && chunk_->chunk_state == CHUNK_ALLOCATED;
+}
 uptr AsanChunkView::Beg() { return chunk_->Beg(); }
 uptr AsanChunkView::End() { return Beg() + UsedSize(); }
 uptr AsanChunkView::UsedSize() { return chunk_->UsedSize(); }


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