base/allocator: Intercept strdup on Android when use_allocator_shim

On Android, malloc, free, etc. are intercepted by using the
linker option -Wl,-wrap,FUNC , which means we're intercepting
only the symbols undefined at link time.  Non-undefined symbols
like a call to malloc inside libc are not intercepted.

strdup and strndup are such functions that internally call to
malloc.  However, the return values of strdup/strndup are
deallocated with free (= our own free), so we should intercept
strdup/strndup to have them use our own malloc.

This patch implements wrapper functions for strdup/strndup just
like one for malloc.

Bug: 1111332
Change-Id: I5747a2c32f19bb63c0380f10f589b9a8f6dd3b19
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2418513Reviewed-by: Kentaro Hara <haraken@chromium.org>
Reviewed-by: Benoit L <lizeb@chromium.org>
Reviewed-by: Bartek Nowierski <bartekn@chromium.org>
Commit-Queue: Yuki Shiino <yukishiino@chromium.org>
Cr-Commit-Position: refs/heads/master@{#808861}

base/allocator/BUILD.gn

@@ -296,5 +296,9 @@ config("wrap_malloc_symbols") {
     "-Wl,-wrap,pvalloc",
     "-Wl,-wrap,realloc",
     "-Wl,-wrap,valloc",
+
+    # <string.h> functions
+    "-Wl,-wrap,strdup",
+    "-Wl,-wrap,strndup",
   ]
 }

base/allocator/allocator_shim_override_linker_wrapped_symbols.h

@@ -13,6 +13,9 @@
 // -wrap linker flags (e.g., libchrome.so) will be rewritten to the
 // linker as references to __wrap_malloc, __wrap_free, which are defined here.
 
+#include <algorithm>
+#include <cstring>
+
 #include "base/allocator/allocator_shim_internals.h"
 
 extern "C" {
@@ -51,4 +54,24 @@ SHIM_ALWAYS_EXPORT void* __wrap_valloc(size_t size) {
   return ShimValloc(size, nullptr);
 }
 
+// Override <string.h> functions
+
+SHIM_ALWAYS_EXPORT char* __wrap_strdup(const char* str) {
+  std::size_t length = std::strlen(str) + 1;
+  void* buffer = ShimMalloc(length, nullptr);
+  if (!buffer)
+    return nullptr;
+  return reinterpret_cast<char*>(std::memcpy(buffer, str, length));
+}
+
+SHIM_ALWAYS_EXPORT char* __wrap_strndup(const char* str, size_t n) {
+  std::size_t length = std::min(std::strlen(str), n);
+  char* buffer = reinterpret_cast<char*>(ShimMalloc(length + 1, nullptr));
+  if (!buffer)
+    return nullptr;
+  std::memcpy(buffer, str, length);
+  buffer[length] = '\0';
+  return buffer;
+}
+
 }  // extern "C"