diff --git a/libc/bionic/grp_pwd_file.cpp b/libc/bionic/grp_pwd_file.cpp
new file mode 100644
index 0000000..911daea
--- /dev/null
+++ b/libc/bionic/grp_pwd_file.cpp
@@ -0,0 +1,326 @@
+/*
+ * Copyright (C) 2018 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 "grp_pwd_file.h"
+
+#include <fcntl.h>
+#include <stdlib.h>
+#include <sys/mman.h>
+#include <sys/stat.h>
+
+#include "private/ErrnoRestorer.h"
+
+// This file mmap's /*/etc/passwd and /*/etc/group in order to return their contents without any
+// allocations.  Note that these files and the strings contained within them are explicitly not
+// null-terminated.  ':'s are used to deliminate fields and '\n's are used to deliminate lines.
+// There is a check that the file ends with '\n', such that terminating loops at '\n' ensures that
+// memory will be not ready before the mmap region.
+
+namespace {
+
+void CopyFieldToString(char* dest, const char* source, size_t max) {
+  while (*source != ':' && *source != '\n' && max > 1) {
+    *dest++ = *source++;
+    --max;
+  }
+  *dest = '\0';
+}
+
+bool FieldToUid(const char* field, uid_t* uid) {
+  if (field == nullptr) {
+    return false;
+  }
+
+  char* end = nullptr;
+  errno = 0;
+  uid_t result = strtoul(field, &end, 0);
+  if (errno != 0 || field == end || *end != ':') {
+    return false;
+  }
+  *uid = result;
+  return true;
+}
+
+// Returns a pointer to one past the end of line.
+const char* ParseLine(const char* begin, const char* end, const char** fields, size_t num_fields) {
+  size_t fields_written = 0;
+  const char* position = begin;
+  fields[fields_written++] = position;
+
+  while (position < end && fields_written < num_fields) {
+    if (*position == '\n') {
+      return position + 1;
+    }
+    if (*position == ':') {
+      fields[fields_written++] = position + 1;
+    }
+    position++;
+  }
+
+  while (position < end && *position != '\n') {
+    position++;
+  }
+
+  return position + 1;
+}
+
+struct PasswdLine {
+  const char* name() const {
+    return fields[0];
+  }
+  // Password is not supported.
+  const char* uid() const {
+    return fields[2];
+  }
+  const char* gid() const {
+    return fields[3];
+  }
+  // User Info is not supported
+  const char* dir() const {
+    return fields[5];
+  }
+  const char* shell() const {
+    return fields[6];
+  }
+
+  bool ToPasswdState(passwd_state_t* passwd_state) {
+    if (name() == nullptr || dir() == nullptr || shell() == nullptr) {
+      return false;
+    }
+
+    uid_t uid;
+    if (!FieldToUid(this->uid(), &uid)) {
+      return false;
+    }
+
+    gid_t gid;
+    if (!FieldToUid(this->gid(), &gid)) {
+      return false;
+    }
+
+    passwd_state->passwd_.pw_uid = uid;
+    passwd_state->passwd_.pw_gid = gid;
+
+    CopyFieldToString(passwd_state->name_buffer_, name(), sizeof(passwd_state->name_buffer_));
+    passwd_state->passwd_.pw_name = passwd_state->name_buffer_;
+
+    passwd_state->passwd_.pw_passwd = nullptr;
+
+#ifdef __LP64__
+    passwd_state->passwd_.pw_gecos = nullptr;
+#endif
+
+    CopyFieldToString(passwd_state->dir_buffer_, dir(), sizeof(passwd_state->dir_buffer_));
+    passwd_state->passwd_.pw_dir = passwd_state->dir_buffer_;
+
+    CopyFieldToString(passwd_state->sh_buffer_, shell(), sizeof(passwd_state->sh_buffer_));
+    passwd_state->passwd_.pw_shell = passwd_state->sh_buffer_;
+
+    return true;
+  }
+
+  static constexpr size_t kNumFields = 7;
+  const char* fields[kNumFields] = {};
+};
+
+struct GroupLine {
+  const char* name() const {
+    return fields[0];
+  }
+  // Password is not supported.
+  const char* gid() const {
+    return fields[2];
+  }
+  // User list is not supported (returns simply name)
+
+  bool ToGroupState(group_state_t* group_state) {
+    if (name() == nullptr || gid() == nullptr) {
+      return false;
+    }
+
+    gid_t gid;
+    if (!FieldToUid(this->gid(), &gid)) {
+      return false;
+    }
+
+    group_state->group_.gr_gid = gid;
+
+    CopyFieldToString(group_state->group_name_buffer_, name(),
+                      sizeof(group_state->group_name_buffer_));
+    group_state->group_.gr_name = group_state->group_name_buffer_;
+
+    group_state->group_.gr_passwd = nullptr;
+
+    group_state->group_.gr_mem = group_state->group_members_;
+    group_state->group_.gr_mem[0] = group_state->group_.gr_name;
+    group_state->group_.gr_mem[1] = nullptr;
+
+    return true;
+  }
+
+  static constexpr size_t kNumFields = 4;
+  const char* fields[kNumFields] = {};
+};
+
+}  // namespace
+
+MmapFile::MmapFile(const char* filename) : filename_(filename) {
+  lock_.init(false);
+}
+
+MmapFile::~MmapFile() {
+  if (status_ == FileStatus::Initialized) {
+    size_t size = end_ - start_ + 1;
+    munmap(const_cast<char*>(start_), size);
+  }
+}
+
+bool MmapFile::GetFile(const char** start, const char** end) {
+  LockGuard guard(lock_);
+  if (status_ == FileStatus::Initialized) {
+    *start = start_;
+    *end = end_;
+    return true;
+  }
+  if (status_ == FileStatus::Error) {
+    return false;
+  }
+
+  if (!DoMmap()) {
+    status_ = FileStatus::Error;
+    return false;
+  }
+
+  status_ = FileStatus::Initialized;
+  *start = start_;
+  *end = end_;
+  return true;
+}
+
+bool MmapFile::DoMmap() {
+  int fd = open(filename_, O_CLOEXEC | O_NOFOLLOW | O_RDONLY);
+
+  struct stat fd_stat;
+  if (fstat(fd, &fd_stat) == -1) {
+    close(fd);
+    return false;
+  }
+
+  auto mmap_size = fd_stat.st_size;
+
+  const void* map_result = mmap(nullptr, mmap_size, PROT_READ, MAP_SHARED, fd, 0);
+  close(fd);
+
+  if (map_result == MAP_FAILED) {
+    return false;
+  }
+
+  start_ = static_cast<const char*>(map_result);
+  end_ = start_ + mmap_size - 1;
+
+  return *end_ == '\n';
+}
+
+template <typename Line, typename Predicate>
+bool MmapFile::Find(Line* line, Predicate predicate) {
+  const char* start;
+  const char* end;
+  if (!GetFile(&start, &end)) {
+    return false;
+  }
+
+  const char* line_beginning = start;
+
+  while (line_beginning < end) {
+    line_beginning = ParseLine(line_beginning, end, line->fields, line->kNumFields);
+    if (predicate(line)) return true;
+  }
+
+  return false;
+}
+
+template <typename Line>
+bool MmapFile::FindById(uid_t uid, Line* line) {
+  return Find(line, [uid](const auto& line) {
+    uid_t line_id;
+    if (!FieldToUid(line->fields[2], &line_id)) {
+      return false;
+    }
+
+    return line_id == uid;
+  });
+}
+
+template <typename Line>
+bool MmapFile::FindByName(const char* name, Line* line) {
+  return Find(line, [name](const auto& line) {
+    const char* line_name = line->fields[0];
+    if (line_name == nullptr) {
+      return false;
+    }
+
+    const char* match_name = name;
+    while (*line_name != '\n' && *line_name != ':' && *match_name != '\0') {
+      if (*line_name++ != *match_name++) {
+        return false;
+      }
+    }
+
+    return *line_name == ':' && *match_name == '\0';
+  });
+}
+
+PasswdFile::PasswdFile(const char* filename) : mmap_file_(filename) {
+}
+
+bool PasswdFile::FindById(uid_t id, passwd_state_t* passwd_state) {
+  ErrnoRestorer errno_restorer;
+  PasswdLine passwd_line;
+  return mmap_file_.FindById(id, &passwd_line) && passwd_line.ToPasswdState(passwd_state);
+}
+
+bool PasswdFile::FindByName(const char* name, passwd_state_t* passwd_state) {
+  ErrnoRestorer errno_restorer;
+  PasswdLine passwd_line;
+  return mmap_file_.FindByName(name, &passwd_line) && passwd_line.ToPasswdState(passwd_state);
+}
+
+GroupFile::GroupFile(const char* filename) : mmap_file_(filename) {
+}
+
+bool GroupFile::FindById(gid_t id, group_state_t* group_state) {
+  ErrnoRestorer errno_restorer;
+  GroupLine group_line;
+  return mmap_file_.FindById(id, &group_line) && group_line.ToGroupState(group_state);
+}
+
+bool GroupFile::FindByName(const char* name, group_state_t* group_state) {
+  ErrnoRestorer errno_restorer;
+  GroupLine group_line;
+  return mmap_file_.FindByName(name, &group_line) && group_line.ToGroupState(group_state);
+}