Split system_properties.cpp into its component pieces

system_properties.cpp is a little bit unmanageable in its current
form, and is overdue for a refactoring into more clearly defined
components.

Of particular interest, is creating of a Contexts interface that
handles mapping of system property name -> SEContext and its
associated prop_area, and creating two classes that implement the
current and legacy functionality.  This is needed as there will likely
be a third even newer way to do this mapping.

Bug: 36001741
Test: boot bullhead, system property unit tests
Change-Id: Ie75ec6fea1a95f90813918f54669d533e51327c6

1 files changed, 355 insertions, 0 deletions

diff --git a/libc/system_properties/contexts_split.cpp b/libc/system_properties/contexts_split.cpp
new file mode 100644
index 000000000..964a1e436
--- /dev/null
+++ b/libc/system_properties/contexts_split.cpp
@@ -0,0 +1,355 @@
+/*
+ * Copyright (C) 2008 The Android Open Source Project
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *  * Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ *  * Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in
+ *    the documentation and/or other materials provided with the
+ *    distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+ * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+ * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
+ * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
+ * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
+ * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#include "contexts_split.h"
+
+#include <ctype.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/mman.h>
+#include <sys/stat.h>
+
+#include <async_safe/log.h>
+
+#include "context_node.h"
+#include "system_property_globals.h"
+
+class ContextListNode : public ContextNode {
+ public:
+  ContextListNode(ContextListNode* next, const char* context)
+      : ContextNode(strdup(context)), next(next) {
+  }
+
+  ~ContextListNode() {
+    free(const_cast<char*>(context()));
+  }
+
+  ContextListNode* next;
+};
+
+struct PrefixNode {
+  PrefixNode(struct PrefixNode* next, const char* prefix, ContextListNode* context)
+      : prefix(strdup(prefix)), prefix_len(strlen(prefix)), context(context), next(next) {
+  }
+  ~PrefixNode() {
+    free(prefix);
+  }
+  char* prefix;
+  const size_t prefix_len;
+  ContextListNode* context;
+  PrefixNode* next;
+};
+
+template <typename List, typename... Args>
+static inline void ListAdd(List** list, Args... args) {
+  *list = new List(*list, args...);
+}
+
+static void ListAddAfterLen(PrefixNode** list, const char* prefix, ContextListNode* context) {
+  size_t prefix_len = strlen(prefix);
+
+  auto next_list = list;
+
+  while (*next_list) {
+    if ((*next_list)->prefix_len < prefix_len || (*next_list)->prefix[0] == '*') {
+      ListAdd(next_list, prefix, context);
+      return;
+    }
+    next_list = &(*next_list)->next;
+  }
+  ListAdd(next_list, prefix, context);
+}
+
+template <typename List, typename Func>
+static void ListForEach(List* list, Func func) {
+  while (list) {
+    func(list);
+    list = list->next;
+  }
+}
+
+template <typename List, typename Func>
+static List* ListFind(List* list, Func func) {
+  while (list) {
+    if (func(list)) {
+      return list;
+    }
+    list = list->next;
+  }
+  return nullptr;
+}
+
+template <typename List>
+static void ListFree(List** list) {
+  while (*list) {
+    auto old_list = *list;
+    *list = old_list->next;
+    delete old_list;
+  }
+}
+
+// The below two functions are duplicated from label_support.c in libselinux.
+// TODO: Find a location suitable for these functions such that both libc and
+// libselinux can share a common source file.
+
+// The read_spec_entries and read_spec_entry functions may be used to
+// replace sscanf to read entries from spec files. The file and
+// property services now use these.
+
+// Read an entry from a spec file (e.g. file_contexts)
+static inline int read_spec_entry(char** entry, char** ptr, int* len) {
+  *entry = nullptr;
+  char* tmp_buf = nullptr;
+
+  while (isspace(**ptr) && **ptr != '\0') (*ptr)++;
+
+  tmp_buf = *ptr;
+  *len = 0;
+
+  while (!isspace(**ptr) && **ptr != '\0') {
+    (*ptr)++;
+    (*len)++;
+  }
+
+  if (*len) {
+    *entry = strndup(tmp_buf, *len);
+    if (!*entry) return -1;
+  }
+
+  return 0;
+}
+
+// line_buf - Buffer containing the spec entries .
+// num_args - The number of spec parameter entries to process.
+// ...      - A 'char **spec_entry' for each parameter.
+// returns  - The number of items processed.
+//
+// This function calls read_spec_entry() to do the actual string processing.
+static int read_spec_entries(char* line_buf, int num_args, ...) {
+  char **spec_entry, *buf_p;
+  int len, rc, items, entry_len = 0;
+  va_list ap;
+
+  len = strlen(line_buf);
+  if (line_buf[len - 1] == '\n')
+    line_buf[len - 1] = '\0';
+  else
+    // Handle case if line not \n terminated by bumping
+    // the len for the check below (as the line is NUL
+    // terminated by getline(3))
+    len++;
+
+  buf_p = line_buf;
+  while (isspace(*buf_p)) buf_p++;
+
+  // Skip comment lines and empty lines.
+  if (*buf_p == '#' || *buf_p == '\0') return 0;
+
+  // Process the spec file entries
+  va_start(ap, num_args);
+
+  items = 0;
+  while (items < num_args) {
+    spec_entry = va_arg(ap, char**);
+
+    if (len - 1 == buf_p - line_buf) {
+      va_end(ap);
+      return items;
+    }
+
+    rc = read_spec_entry(spec_entry, &buf_p, &entry_len);
+    if (rc < 0) {
+      va_end(ap);
+      return rc;
+    }
+    if (entry_len) items++;
+  }
+  va_end(ap);
+  return items;
+}
+
+static bool MapSystemPropertyArea(bool access_rw, bool* fsetxattr_failed) {
+  char filename[PROP_FILENAME_MAX];
+  int len = async_safe_format_buffer(filename, sizeof(filename), "%s/properties_serial",
+                                     property_filename);
+  if (len < 0 || len > PROP_FILENAME_MAX) {
+    __system_property_area__ = nullptr;
+    return false;
+  }
+
+  if (access_rw) {
+    __system_property_area__ =
+        prop_area::map_prop_area_rw(filename, "u:object_r:properties_serial:s0", fsetxattr_failed);
+  } else {
+    __system_property_area__ = prop_area::map_prop_area(filename);
+  }
+  return __system_property_area__;
+}
+
+bool ContextsSplit::InitializePropertiesFromFile(const char* filename) {
+  FILE* file = fopen(filename, "re");
+  if (!file) {
+    return false;
+  }
+
+  char* buffer = nullptr;
+  size_t line_len;
+  char* prop_prefix = nullptr;
+  char* context = nullptr;
+
+  while (getline(&buffer, &line_len, file) > 0) {
+    int items = read_spec_entries(buffer, 2, &prop_prefix, &context);
+    if (items <= 0) {
+      continue;
+    }
+    if (items == 1) {
+      free(prop_prefix);
+      continue;
+    }
+
+    // init uses ctl.* properties as an IPC mechanism and does not write them
+    // to a property file, therefore we do not need to create property files
+    // to store them.
+    if (!strncmp(prop_prefix, "ctl.", 4)) {
+      free(prop_prefix);
+      free(context);
+      continue;
+    }
+
+    auto old_context = ListFind(
+        contexts_, [context](ContextListNode* l) { return !strcmp(l->context(), context); });
+    if (old_context) {
+      ListAddAfterLen(&prefixes_, prop_prefix, old_context);
+    } else {
+      ListAdd(&contexts_, context);
+      ListAddAfterLen(&prefixes_, prop_prefix, contexts_);
+    }
+    free(prop_prefix);
+    free(context);
+  }
+
+  free(buffer);
+  fclose(file);
+
+  return true;
+}
+
+bool ContextsSplit::InitializeProperties() {
+  // If we do find /property_contexts, then this is being
+  // run as part of the OTA updater on older release that had
+  // /property_contexts - b/34370523
+  if (InitializePropertiesFromFile("/property_contexts")) {
+    return true;
+  }
+
+  // Use property_contexts from /system & /vendor, fall back to those from /
+  if (access("/system/etc/selinux/plat_property_contexts", R_OK) != -1) {
+    if (!InitializePropertiesFromFile("/system/etc/selinux/plat_property_contexts")) {
+      return false;
+    }
+    // Don't check for failure here, so we always have a sane list of properties.
+    // E.g. In case of recovery, the vendor partition will not have mounted and we
+    // still need the system / platform properties to function.
+    InitializePropertiesFromFile("/vendor/etc/selinux/nonplat_property_contexts");
+  } else {
+    if (!InitializePropertiesFromFile("/plat_property_contexts")) {
+      return false;
+    }
+    InitializePropertiesFromFile("/nonplat_property_contexts");
+  }
+
+  return true;
+}
+
+bool ContextsSplit::Initialize(bool writable) {
+  if (!InitializeProperties()) {
+    return false;
+  }
+
+  if (writable) {
+    mkdir(property_filename, S_IRWXU | S_IXGRP | S_IXOTH);
+    bool open_failed = false;
+    bool fsetxattr_failed = false;
+    ListForEach(contexts_, [&fsetxattr_failed, &open_failed](ContextListNode* l) {
+      if (!l->Open(true, &fsetxattr_failed)) {
+        open_failed = true;
+      }
+    });
+    if (open_failed || !MapSystemPropertyArea(true, &fsetxattr_failed)) {
+      FreeAndUnmap();
+      return false;
+    }
+
+    return !fsetxattr_failed;
+  } else {
+    if (!MapSystemPropertyArea(false, nullptr)) {
+      FreeAndUnmap();
+      return false;
+    }
+  }
+  return true;
+}
+
+prop_area* ContextsSplit::GetPropAreaForName(const char* name) {
+  auto entry = ListFind(prefixes_, [name](PrefixNode* l) {
+    return l->prefix[0] == '*' || !strncmp(l->prefix, name, l->prefix_len);
+  });
+  if (!entry) {
+    return nullptr;
+  }
+
+  auto cnode = entry->context;
+  if (!cnode->pa()) {
+    // We explicitly do not check no_access_ in this case because unlike the
+    // case of foreach(), we want to generate an selinux audit for each
+    // non-permitted property access in this function.
+    cnode->Open(false, nullptr);
+  }
+  return cnode->pa();
+}
+
+void ContextsSplit::ForEach(void (*propfn)(const prop_info* pi, void* cookie), void* cookie) {
+  ListForEach(contexts_, [propfn, cookie](ContextListNode* l) {
+    if (l->CheckAccessAndOpen()) {
+      l->pa()->foreach (propfn, cookie);
+    }
+  });
+}
+
+void ContextsSplit::ResetAccess() {
+  ListForEach(contexts_, [](ContextListNode* l) { l->ResetAccess(); });
+}
+
+void ContextsSplit::FreeAndUnmap() {
+  ListFree(&prefixes_);
+  ListFree(&contexts_);
+  if (__system_property_area__) {
+    munmap(__system_property_area__, pa_size);
+    __system_property_area__ = nullptr;
+  }
+}