Add support for disabling the greylist.

Useful for testing whether apps have actually stopped using greylisted
libraries even if they still have references to them in their apk to support
old Android releases but also haven't bumped their targetSdkVersion yet.

Since we already have two expensive __system_property_get calls and this
would add a third, optimize two (but leave the third since it's not
obviously amenable to optimization). None of this matters for user builds,
but I don't want userdebug/eng to have distractingly different performance.

(cherrypick of 7933bec2872aa1c3430149c7649726333c0ac9d8.)

Bug: http://b/36106661
Test: ran "can you escape 5" with and without this property
Change-Id: Id9a804695c1dca9b4be2ebd0e72f01817bb13cba

1 files changed, 44 insertions, 40 deletions

diff --git a/linker/linker_logger.cpp b/linker/linker_logger.cpp
index b2ea320ea..717667ca8 100644
--- a/linker/linker_logger.cpp
+++ b/linker/linker_logger.cpp
@@ -26,32 +26,21 @@
  * SUCH DAMAGE.
  */
 
+#include "linker_logger.h"
+
 #include <string.h>
 #include <sys/prctl.h>
-#include <sys/system_properties.h>
 #include <unistd.h>
 
 #include <string>
 #include <vector>
 
 #include "android-base/strings.h"
-#include "linker_logger.h"
+#include "private/CachedProperty.h"
 #include "private/libc_logging.h"
 
 LinkerLogger g_linker_logger;
-
-static const char* kSystemLdDebugProperty = "debug.ld.all";
-static const char* kLdDebugPropertyPrefix = "debug.ld.app.";
-
-static const char* kOptionErrors = "dlerror";
-static const char* kOptionDlopen = "dlopen";
-static const char* kOptionDlsym = "dlsym";
-
-static std::string property_get(const char* name) {
-  char value[PROP_VALUE_MAX] = {};
-  __system_property_get(name, value);
-  return value;
-}
+bool g_greylist_disabled = false;
 
 static uint32_t ParseProperty(const std::string& value) {
   if (value.empty()) {
@@ -63,53 +52,69 @@ static uint32_t ParseProperty(const std::string& value) {
   uint32_t flags = 0;
 
   for (const auto& o : options) {
-    if (o == kOptionErrors) {
+    if (o == "dlerror") {
       flags |= kLogErrors;
-    } else if (o == kOptionDlopen){
+    } else if (o == "dlopen") {
       flags |= kLogDlopen;
-    } else if (o == kOptionDlsym){
+    } else if (o == "dlsym") {
       flags |= kLogDlsym;
     } else {
-      __libc_format_log(ANDROID_LOG_WARN, "linker", "Unknown debug.ld option \"%s\", will ignore.", o.c_str());
+      __libc_format_log(ANDROID_LOG_WARN, "linker", "Ignoring unknown debug.ld option \"%s\"",
+                        o.c_str());
     }
   }
 
   return flags;
 }
 
+static void GetAppSpecificProperty(char* buffer) {
+  // Get process basename.
+  const char* process_name_start = basename(g_argv[0]);
+
+  // Remove ':' and everything after it. This is the naming convention for
+  // services: https://developer.android.com/guide/components/services.html
+  const char* process_name_end = strchr(process_name_start, ':');
+
+  std::string process_name = (process_name_end != nullptr) ?
+                             std::string(process_name_start, (process_name_end - process_name_start)) :
+                             std::string(process_name_start);
+
+  std::string property_name = std::string("debug.ld.app.") + process_name;
+  __system_property_get(property_name.c_str(), buffer);
+}
+
 void LinkerLogger::ResetState() {
-  // the most likely scenario app is not debuggable and
-  // is running on user build - the logging is disabled.
+  // The most likely scenario app is not debuggable and
+  // is running on a user build, in which case logging is disabled.
   if (prctl(PR_GET_DUMPABLE, 0, 0, 0, 0) == 0) {
     return;
   }
 
+  // This is a convenient place to check whether the greylist should be disabled for testing.
+  static CachedProperty greylist_disabled("debug.ld.greylist_disabled");
+  bool old_value = g_greylist_disabled;
+  g_greylist_disabled = (strcmp(greylist_disabled.Get(), "true") == 0);
+  if (g_greylist_disabled != old_value) {
+    __libc_format_log(ANDROID_LOG_INFO, "linker", "%s greylist",
+                      g_greylist_disabled ? "Disabling" : "Enabling");
+  }
+
   flags_ = 0;
 
-  // Check flag applied to all processes first.
-  std::string value = property_get(kSystemLdDebugProperty);
-  flags_ |= ParseProperty(value);
+  // For logging, check the flag applied to all processes first.
+  static CachedProperty debug_ld_all("debug.ld.all");
+  flags_ |= ParseProperty(debug_ld_all.Get());
 
   // Ignore processes started without argv (http://b/33276926).
   if (g_argv[0] == nullptr) {
     return;
   }
 
-  // Get process basename.
-  const char* process_name_start = basename(g_argv[0]);
-
-  // Remove ':' and everything after it. This is the naming convention for
-  // services: https://developer.android.com/guide/components/services.html
-  const char* process_name_end = strchr(process_name_start, ':');
-
-  std::string process_name = (process_name_end != nullptr) ?
-                             std::string(process_name_start, (process_name_end - process_name_start)) :
-                             std::string(process_name_start);
-
-  std::string property_name = std::string(kLdDebugPropertyPrefix) + process_name;
-
-  value = property_get(property_name.c_str());
-  flags_ |= ParseProperty(value);
+  // Otherwise check the app-specific property too.
+  // We can't easily cache the property here because argv[0] changes.
+  char debug_ld_app[PROP_VALUE_MAX] = {};
+  GetAppSpecificProperty(debug_ld_app);
+  flags_ |= ParseProperty(debug_ld_app);
 }
 
 void LinkerLogger::Log(uint32_t type, const char* format, ...) {
@@ -122,4 +127,3 @@ void LinkerLogger::Log(uint32_t type, const char* format, ...) {
   __libc_format_log_va_list(ANDROID_LOG_DEBUG, "linker", format, ap);
   va_end(ap);
 }
-