libc/bionic/grp_pwd_file.cpp - android_bionic - Gitiles

 /*
  * 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 <string.h>
 #include <sys/mman.h>
 #include <sys/stat.h>

 #include <async_safe/log.h>

 #include "private/ErrnoRestorer.h"
 #include "private/ScopedFd.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 read beyond 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, const char* required_prefix)
     : filename_(filename), required_prefix_(required_prefix) {
   lock_.init(false);
 }

 void MmapFile::Unmap() {
   if (status_ == FileStatus::Initialized) {
     size_t size = end_ - start_ + 1;
     munmap(const_cast<char*>(start_), size);
     status_ = FileStatus::Uninitialized;
     start_ = nullptr;
     end_ = nullptr;
   }
 }

 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() {
   ScopedFd fd(open(filename_, O_CLOEXEC | O_NOFOLLOW | O_RDONLY));

   struct stat fd_stat;
   if (fstat(fd.get(), &fd_stat) == -1) {
     return false;
   }

   auto mmap_size = fd_stat.st_size;

   void* map_result = mmap(nullptr, mmap_size, PROT_READ, MAP_SHARED, fd.get(), 0);
   if (map_result == MAP_FAILED) {
     return false;
   }

   start_ = static_cast<const char*>(map_result);
   end_ = start_ + mmap_size - 1;

   if (*end_ != '\n') {
     munmap(map_result, mmap_size);
     return false;
   }

   return true;
 }

 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 defined(__ANDROID__)
     // To comply with Treble, users/groups from each partition need to be prefixed with
     // the partition name.
     if (required_prefix_ != nullptr) {
       if (strncmp(line->fields[0], required_prefix_, strlen(required_prefix_)) != 0) {
         char name[kGrpPwdBufferSize];
         CopyFieldToString(name, line->fields[0], sizeof(name));
         async_safe_format_log(ANDROID_LOG_ERROR, "libc",
                               "Found user/group name '%s' in '%s' without required prefix '%s'",
                               name, filename_, required_prefix_);
         continue;
       }
     }
 #endif
     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, const char* required_prefix)
     : mmap_file_(filename, required_prefix) {
 }

 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, const char* required_prefix)
     : mmap_file_(filename, required_prefix) {
 }

 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);
 }
	/*
	* 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 <string.h>
	#include <sys/mman.h>
	#include <sys/stat.h>

	#include <async_safe/log.h>

	#include "private/ErrnoRestorer.h"
	#include "private/ScopedFd.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 read beyond 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, const char* required_prefix)
	: filename_(filename), required_prefix_(required_prefix) {
	lock_.init(false);
	}

	void MmapFile::Unmap() {
	if (status_ == FileStatus::Initialized) {
	size_t size = end_ - start_ + 1;
	munmap(const_cast<char*>(start_), size);
	status_ = FileStatus::Uninitialized;
	start_ = nullptr;
	end_ = nullptr;
	}
	}

	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() {
	ScopedFd fd(open(filename_, O_CLOEXEC \| O_NOFOLLOW \| O_RDONLY));

	struct stat fd_stat;
	if (fstat(fd.get(), &fd_stat) == -1) {
	return false;
	}

	auto mmap_size = fd_stat.st_size;

	void* map_result = mmap(nullptr, mmap_size, PROT_READ, MAP_SHARED, fd.get(), 0);
	if (map_result == MAP_FAILED) {
	return false;
	}

	start_ = static_cast<const char*>(map_result);
	end_ = start_ + mmap_size - 1;

	if (*end_ != '\n') {
	munmap(map_result, mmap_size);
	return false;
	}

	return true;
	}

	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 defined(__ANDROID__)
	// To comply with Treble, users/groups from each partition need to be prefixed with
	// the partition name.
	if (required_prefix_ != nullptr) {
	if (strncmp(line->fields[0], required_prefix_, strlen(required_prefix_)) != 0) {
	char name[kGrpPwdBufferSize];
	CopyFieldToString(name, line->fields[0], sizeof(name));
	async_safe_format_log(ANDROID_LOG_ERROR, "libc",
	"Found user/group name '%s' in '%s' without required prefix '%s'",
	name, filename_, required_prefix_);
	continue;
	}
	}
	#endif
	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, const char* required_prefix)
	: mmap_file_(filename, required_prefix) {
	}

	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, const char* required_prefix)
	: mmap_file_(filename, required_prefix) {
	}

	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);
	}