[asan] Correctly release memory allocated during early startup.

[ygribov]

Summary

Inspired by https://github.com/google/sanitizers/issues/626

Calloc interceptor initially allocates memory from temp buffer (to serve dlsyms called during asan_init). There is a chance that some non-instrumented library (or executable) has allocated memory with calloc before asan_init and got pointer from the same temporary buffer which later caused problems with free.

[ygribov]

Added UNLIKELY hints.

[samsonov]

lib/asan/asan_malloc_linux.cc

33

Wait, why is it not ptr - calloc_memory_for_dlsym?

74

It's not that hard to keep sizes of the allocations from calloc_memory_for_dlsym. E.g. when you return &calloc_memory_for_dlsym[allocated] you can store size_in_words in calloc_memory_for_dlsym_sizes[allocated].

test/asan/TestCases/Linux/calloc-preload.c

10

UNSUPPORTED: android
?

[ygribov]

Fixed Alexey's remarks.

[ygribov]

lib/asan/asan_malloc_linux.cc

33

Right, shame on me. This worked because ptr was equal to calloc_memory_for_dlsym.

74

Sure, but is it worth it? We do not expect pool pointers to sneak into normal allocator very often.

test/asan/TestCases/Linux/calloc-preload.c

12

That's Evgeniy's code, also used in other tests. Perhaps fix this in separate commit?

[eugenis]

test/asan/TestCases/Linux/calloc-preload.c

12

Yes, this should be replaced with UNSUPPORTED. Other occurrencies could be fixed in a separate commit, but there no reason to use not-android in newly added tests.

[samsonov]

Looks OK, but please fix the bug pointed out below.

lib/asan/asan_malloc_linux.cc

73

ptr - calloc_memory_for_dlsym here as well

74

Okay

[ygribov]

lib/asan/asan_malloc_linux.cc

73

Done.

lib/asan/asan_malloc_linux.cc

 #include "asan_allocator.h"
 #include "asan_interceptors.h"
 #include "asan_internal.h"
 #include "asan_stack.h"
 
 // ---------------------- Replacement functions ---------------- {{{1
 using namespace __asan;  // NOLINT
 
+static const uptr kCallocPoolSize = 1024;
+static uptr calloc_memory_for_dlsym[kCallocPoolSize];
+
+static bool IsInCallocPool(const void *ptr) {
+  sptr off = (sptr)calloc_memory_for_dlsym - (sptr)ptr;
+  return 0 <= off && off < (sptr)kCallocPoolSize;
+}
+
 INTERCEPTOR(void, free, void *ptr) {
   GET_STACK_TRACE_FREE;
+  if (UNLIKELY(IsInCallocPool(ptr)))
+    return;
   asan_free(ptr, &stack, FROM_MALLOC);
 }
 
 INTERCEPTOR(void, cfree, void *ptr) {
   GET_STACK_TRACE_FREE;
+  if (UNLIKELY(IsInCallocPool(ptr)))
+    return;
   asan_free(ptr, &stack, FROM_MALLOC);
 }
 
 INTERCEPTOR(void*, malloc, uptr size) {
   GET_STACK_TRACE_MALLOC;
   return asan_malloc(size, &stack);
 }
 
 INTERCEPTOR(void*, calloc, uptr nmemb, uptr size) {
   if (UNLIKELY(!asan_inited)) {
     // Hack: dlsym calls calloc before REAL(calloc) is retrieved from dlsym.
-    const uptr kCallocPoolSize = 1024;
-    static uptr calloc_memory_for_dlsym[kCallocPoolSize];
     static uptr allocated;
     uptr size_in_words = ((nmemb * size) + kWordSize - 1) / kWordSize;
     void *mem = (void*)&calloc_memory_for_dlsym[allocated];
     allocated += size_in_words;
     CHECK(allocated < kCallocPoolSize);
     return mem;
   }
   GET_STACK_TRACE_MALLOC;
   return asan_calloc(nmemb, size, &stack);
 }
 
 INTERCEPTOR(void*, realloc, void *ptr, uptr size) {
   GET_STACK_TRACE_MALLOC;
+  if (UNLIKELY(IsInCallocPool(ptr))) {
+    uptr offset = (uptr)calloc_memory_for_dlsym - (uptr)ptr;
+    uptr copy_size = Min(size, kCallocPoolSize - offset);
+    void *new_ptr = asan_malloc(size, &stack);
+    internal_memcpy(new_ptr, ptr, copy_size);
+    return new_ptr;
+  }
   return asan_realloc(ptr, size, &stack);
 }
 
 INTERCEPTOR(void*, memalign, uptr boundary, uptr size) {
   GET_STACK_TRACE_MALLOC;
   return asan_memalign(boundary, size, &stack, FROM_MALLOC);
 }
 

test/asan/TestCases/Linux/calloc-preload.c

+// Test that initially callocked memory is properly freed
+// (see https://github.com/google/sanitizers/issues/626).
+// 
+// RUN: %clang %s -o %t
+// RUN: env LD_PRELOAD=%shared_libasan %run %t
+//
+// REQUIRES: asan-dynamic-runtime
+//
+// This way of setting LD_PRELOAD does not work with Android test runner.
+// REQUIRES: not-android
+
+#include <stdio.h>
+#include <stdlib.h>
+
+static void *ptr;
+
+// This constructor will run before __asan_init
+// so calloc will allocate memory from special pool.
+static void init() {
+  ptr = calloc(10, 1);
+}
+
+__attribute__((section(".preinit_array"), used))
+void *dummy = init;
+
+void free_memory() {
+  // This used to abort because
+  // Asan's free didn't recognize ptr.
+  free(ptr);
+}
+
+int main() {
+  free_memory();
+  return 0;
+}
+