Add resetprop magic

native/jni/resetprop/libsystemproperties/include/system_properties/prop_area.h

@@ -110,6 +110,8 @@ class prop_area {
 
   const prop_info* find(const char* name);
   bool add(const char* name, unsigned int namelen, const char* value, unsigned int valuelen);
+  /* resetprop */
+  bool del(const char *name);
 
   bool foreach (void (*propfn)(const prop_info* pi, void* cookie), void* cookie);
 
@@ -124,7 +126,7 @@ class prop_area {
   }
 
  private:
-  static prop_area* map_fd_ro(const int fd);
+  static prop_area* map_fd_rw(const int fd);
 
   void* allocate_obj(const size_t size, uint_least32_t* const off);
   prop_bt* new_prop_bt(const char* name, uint32_t namelen, uint_least32_t* const off);
@@ -138,6 +140,9 @@ class prop_area {
 
   prop_bt* find_prop_bt(prop_bt* const bt, const char* name, uint32_t namelen, bool alloc_if_needed);
 
+  /* resetprop: Traverse through the trie and find the node */
+  prop_bt *find_prop_bt(prop_bt *const trie, const char *name, bool alloc_if_needed);
+
   const prop_info* find_property(prop_bt* const trie, const char* name, uint32_t namelen,
                                  const char* value, uint32_t valuelen, bool alloc_if_needed);
 

native/jni/resetprop/libsystemproperties/include/system_properties/system_properties.h

@@ -66,6 +66,7 @@ class SystemProperties {
   int Get(const char* name, char* value);
   int Update(prop_info* pi, const char* value, unsigned int len);
   int Add(const char* name, unsigned int namelen, const char* value, unsigned int valuelen);
+  int Delete(const char *name);
   uint32_t Serial(const prop_info* pi);
   uint32_t WaitAny(uint32_t old_serial);
   bool Wait(const prop_info* pi, uint32_t old_serial, uint32_t* new_serial_ptr,

native/jni/resetprop/libsystemproperties/prop_area.cpp

@@ -104,7 +104,8 @@ prop_area* prop_area::map_prop_area_rw(const char* filename, const char* context
   return pa;
 }
 
-prop_area* prop_area::map_fd_ro(const int fd) {
+/* resetprop: map_fd_ro -> map_fd_rw */
+prop_area* prop_area::map_fd_rw(const int fd) {
   struct stat fd_stat;
   if (fstat(fd, &fd_stat) < 0) {
     return nullptr;
@@ -119,7 +120,8 @@ prop_area* prop_area::map_fd_ro(const int fd) {
   pa_size_ = fd_stat.st_size;
   pa_data_size_ = pa_size_ - sizeof(prop_area);
 
-  void* const map_result = mmap(nullptr, pa_size_, PROT_READ, MAP_SHARED, fd, 0);
+  /* resetprop: add PROT_WRITE */
+  void* const map_result = mmap(nullptr, pa_size_, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
   if (map_result == MAP_FAILED) {
     return nullptr;
   }
@@ -134,10 +136,11 @@ prop_area* prop_area::map_fd_ro(const int fd) {
 }
 
 prop_area* prop_area::map_prop_area(const char* filename) {
-  int fd = open(filename, O_CLOEXEC | O_NOFOLLOW | O_RDONLY);
+  /* resetprop: O_RDONLY -> O_RDWR */
+  int fd = open(filename, O_CLOEXEC | O_NOFOLLOW | O_RDWR);
   if (fd == -1) return nullptr;
 
-  prop_area* map_result = map_fd_ro(fd);
+  prop_area* map_result = map_fd_rw(fd);
   close(fd);
 
   return map_result;
@@ -272,9 +275,7 @@ prop_bt* prop_area::find_prop_bt(prop_bt* const bt, const char* name, uint32_t n
   }
 }
 
-const prop_info* prop_area::find_property(prop_bt* const trie, const char* name, uint32_t namelen,
+prop_bt *prop_area::find_prop_bt(prop_bt *const trie, const char *name, bool alloc_if_needed) {
-                                          const char* value, uint32_t valuelen,
-                                          bool alloc_if_needed) {
   if (!trie) return nullptr;
 
   const char* remaining_name = name;
@@ -313,6 +314,16 @@ const prop_info* prop_area::find_property(prop_bt* const trie, const char* name,
 
     remaining_name = sep + 1;
   }
+  return current;
+}
+
+const prop_info* prop_area::find_property(prop_bt* const trie, const char* name, uint32_t namelen,
+                                          const char* value, uint32_t valuelen,
+                                          bool alloc_if_needed) {
+  const char* remaining_name = name;
+  prop_bt* current = find_prop_bt(trie, name, alloc_if_needed);
+  if (!current)
+	  return nullptr;
 
   uint_least32_t prop_offset = atomic_load_explicit(&current->prop, memory_order_relaxed);
   if (prop_offset != 0) {
@@ -368,6 +379,14 @@ bool prop_area::add(const char* name, unsigned int namelen, const char* value,
   return find_property(root_node(), name, namelen, value, valuelen, true);
 }
 
+bool prop_area::del(const char *name) {
+  prop_bt* node = find_prop_bt(root_node(), name, false);
+  if (!node)
+    return false;
+  atomic_store_explicit(&node->prop, 0, memory_order_release);
+  return true;
+}
+
 bool prop_area::foreach (void (*propfn)(const prop_info* pi, void* cookie), void* cookie) {
   return foreach_property(root_node(), propfn, cookie);
 }

native/jni/resetprop/libsystemproperties/system_properties.cpp

@@ -63,7 +63,8 @@ bool SystemProperties::Init(const char* filename) {
   ErrnoRestorer errno_restorer;
 
   if (initialized_) {
-    contexts_->ResetAccess();
+    /* resetprop remove */
+    // contexts_->ResetAccess();
     return true;
   }
 
@@ -294,6 +295,36 @@ int SystemProperties::Add(const char* name, unsigned int namelen, const char* va
   return 0;
 }
 
+int SystemProperties::Delete(const char *name) {
+  if (!initialized_) {
+    return -1;
+  }
+
+  prop_area* serial_pa = contexts_->GetSerialPropArea();
+  if (serial_pa == nullptr) {
+    return -1;
+  }
+
+  prop_area* pa = contexts_->GetPropAreaForName(name);
+  if (!pa) {
+    async_safe_format_log(ANDROID_LOG_ERROR, "libc", "Access denied adding property \"%s\"", name);
+    return -1;
+  }
+
+  bool ret = pa->del(name);
+  if (!ret) {
+    return -1;
+  }
+
+  // There is only a single mutator, but we want to make sure that
+  // updates are visible to a reader waiting for the update.
+  atomic_store_explicit(serial_pa->serial(),
+                        atomic_load_explicit(serial_pa->serial(), memory_order_relaxed) + 1,
+                        memory_order_release);
+  __futex_wake(serial_pa->serial(), INT32_MAX);
+  return 0;
+}
+
 // Wait for non-locked serial, and retrieve it with acquire semantics.
 uint32_t SystemProperties::Serial(const prop_info* pi) {
   uint32_t serial = load_const_atomic(&pi->serial, memory_order_acquire);

native/jni/resetprop/private/_system_properties.h

@@ -105,6 +105,12 @@ uint32_t __system_property_area_serial(void);
 */
 int __system_property_add(const char* __name, unsigned int __name_length, const char* __value, unsigned int __value_length);
 
+/* Delete a system property. Added in resetprop
+**
+** Returns 0 on success, -1 if the property area is full.
+*/
+int __system_property_del(const char *__name);
+
 /* Update the value of a system property returned by
 ** __system_property_find.  Can only be done by a single process
 ** that has write access to the property area, and that process

native/jni/resetprop/private/redefs.h

@@ -17,6 +17,5 @@
 #define __system_property_serial __system_property_serial2
 #define __system_properties_init __system_properties_init2
 #define __system_property_wait_any __system_property_wait_any2
-#define __system_property_del(x)  -1  /* Temp disable */
 
 #endif //REDEFS_H

native/jni/resetprop/system_property_api.cpp

@@ -99,6 +99,11 @@ int __system_property_add(const char* name, unsigned int namelen, const char* va
   return system_properties.Add(name, namelen, value, valuelen);
 }
 
+__BIONIC_WEAK_FOR_NATIVE_BRIDGE
+int __system_property_del(const char* name) {
+  return system_properties.Delete(name);
+}
+
 __BIONIC_WEAK_FOR_NATIVE_BRIDGE
 uint32_t __system_property_serial(const prop_info* pi) {
   return system_properties.Serial(pi);