Android: Translate C++ "w" to ParcelFileDescriptor "wt"

Previously we were translating "w" to "w", which unlike in C++ doesn't
truncate. See https://issuetracker.google.com/issues/180526528, and for
reference, https://en.cppreference.com/w/cpp/io/c/fopen and
https://en.cppreference.com/w/cpp/io/basic_filebuf/open.

This issue was brought to my attention by the recently published issue
CVE-2023-21036 in the screenshot editing tool on Pixel phones. I'm not
aware of any code in Dolphin that actually uses "w" with an existing
file on Android (when we ask the user for a location to save to using
SAF, a new file is always created), but still, best to fix this.

1 files changed, 36 insertions, 23 deletions

diff --git a/Source/Android/jni/AndroidCommon/AndroidCommon.cpp b/Source/Android/jni/AndroidCommon/AndroidCommon.cpp
index 00526cc0be..25ec479790 100644
--- a/Source/Android/jni/AndroidCommon/AndroidCommon.cpp
+++ b/Source/Android/jni/AndroidCommon/AndroidCommon.cpp
@@ -12,6 +12,7 @@
 #include <jni.h>
 
 #include "Common/Assert.h"
+#include "Common/Logging/Log.h"
 #include "Common/StringUtil.h"
 #include "jni/AndroidCommon/IDCache.h"
 
@@ -63,38 +64,50 @@ std::string OpenModeToAndroid(std::string mode)
   // The 'b' specifier is not supported by Android. Since we're on POSIX, it's fine to just skip it.
   mode.erase(std::remove(mode.begin(), mode.end(), 'b'));
 
-  if (mode == "r+")
-    mode = "rw";
+  if (mode == "r")
+    return "r";
+  else if (mode == "w")
+    return "wt";
+  else if (mode == "a")
+    return "wa";
+  else if (mode == "r+")
+    return "rw";
   else if (mode == "w+")
-    mode = "rwt";
+    return "rwt";
   else if (mode == "a+")
-    mode = "rwa";
-  else if (mode == "a")
-    mode = "wa";
+    return "rwa";
 
-  return mode;
+  ERROR_LOG_FMT(COMMON, "OpenModeToAndroid(std::string): Unsupported open mode: {}", mode);
+  return "";
 }
 
 std::string OpenModeToAndroid(std::ios_base::openmode mode)
 {
-  std::string result;
-
-  if (mode & std::ios_base::in)
-    result += 'r';
-
-  if (mode & (std::ios_base::out | std::ios_base::app))
-    result += 'w';
-
-  if (mode & std::ios_base::app)
-    result += 'a';
-
-  constexpr std::ios_base::openmode t = std::ios_base::in | std::ios_base::trunc;
-  if ((mode & t) == t)
-    result += 't';
-
   // The 'b' specifier is not supported by Android. Since we're on POSIX, it's fine to just skip it.
+  mode &= ~std::ios_base::binary;
 
-  return result;
+  switch (mode)
+  {
+  case std::ios_base::in:
+    return "r";
+  case std::ios_base::out:
+  case std::ios_base::out | std::ios_base::trunc:
+    return "wt";
+  case std::ios_base::app:
+  case std::ios_base::out | std::ios_base::app:
+    return "wa";
+  case std::ios_base::in | std::ios_base::out:
+    return "rw";
+  case std::ios_base::in | std::ios_base::out | std::ios_base::trunc:
+    return "rwt";
+  case std::ios_base::in | std::ios_base::app:
+  case std::ios_base::in | std::ios_base::out | std::ios_base::app:
+    return "rwa";
+  default:
+    ERROR_LOG_FMT(COMMON,
+                  "OpenModeToAndroid(std::ios_base::openmode): Unsupported open mode: {:#x}", mode);
+    return "";
+  }
 }
 
 int OpenAndroidContent(std::string_view uri, std::string_view mode)