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emacs/lib/euidaccess.c

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Use faccessat, not access, when checking file permissions. This fixes a bug that has been present in Emacs since its creation. It was reported by Chris Torek in 1983 even before GNU Emacs existed, which must set some sort of record. (Torek's bug report was against a predecessor of GNU Emacs, but GNU Emacs happened to have the same common flaw.) See Torek's Usenet posting "setuid/setgid programs & Emacs" Article-I.D.: sri-arpa.858 Posted: Fri Apr 8 14:18:56 1983. * .bzrignore: Add lib/fcntl.h. * configure.ac (euidaccess): Remove check; gnulib does this for us now. (gl_FCNTL_O_FLAGS): Define a dummy version. * lib/at-func.c, lib/euidaccess.c, lib/faccessat.c, lib/fcntl.in.h: * lib/getgroups.c, lib/group-member.c, lib/root-uid.h: * lib/xalloc-oversized.h, m4/euidaccess.m4, m4/faccessat.m4: * m4/fcntl_h.m4, m4/getgroups.m4, m4/group-member.m4: New files, from gnulib. * lib/gnulib.mk, m4/gnulib-comp.m4: Regenerate. * admin/merge-gnulib (GNULIB_MODULES): Add faccessat. (GNULIB_TOOL_FLAGS): Avoid at-internal, fchdir, malloc-posix, openat-die, openat-h, save-cwd. Do not avoid fcntl-h. Omit gnulib's m4/fcntl-o.m4. * nt/inc/ms-w32.h (AT_FDCWD, AT_EACCESS): New symbols. (access): Remove. (faccessat): New macro. * src/Makefile.in (LIB_EACCESS): New macro. (LIBES): Use it. * src/callproc.c (init_callproc): * src/charset.c (init_charset): * src/fileio.c (check_existing, check_executable, check_writable) (Ffile_readable_p): * src/lread.c (openp, load_path_check): * src/process.c (allocate_pty): * src/xrdb.c (file_p): Use effective UID when checking permissions, not real UID. * src/callproc.c (init_callproc): * src/charset.c (init_charset): * src/lread.c (load_path_check, init_lread): Test whether directories are accessible, not merely whether they exist. * src/conf_post.h (GNULIB_SUPPORT_ONLY_AT_FDCWD): New macro. * src/fileio.c (check_existing, check_executable, check_writable) (Ffile_readable_p): Use symbolic names instead of integers for the flags, as they're portable now. (check_writable): New arg AMODE. All uses changed. Set errno on failure. (Ffile_readable_p): Use faccessat, not stat + open + close. (Ffile_writable_p): No need to call check_existing + check_writable. Just call check_writable and then look at errno. This saves a syscall. dir should never be nil; replace an unnecessary runtime check with an eassert. When checking the parent directory of a nonexistent file, check that the directory is searchable as well as writable, as we can't create files in unsearchable directories. (file_directory_p): New function, which uses 'stat' on most platforms but faccessat with D_OK (for efficiency) if WINDOWSNT. (Ffile_directory_p, Fset_file_times): Use it. (file_accessible_directory_p): New function, which uses a single syscall for efficiency. (Ffile_accessible_directory_p): Use it. * src/xrdb.c (file_p): Use file_directory_p. * src/lisp.h (file_directory_p, file_accessible_directory_p): New decls. * src/lread.c (openp): When opening a file, use fstat rather than stat, as that avoids a permissions race. When not opening a file, use file_directory_p rather than stat. (dir_warning): First arg is now a usage string, not a format. Use errno. All uses changed. * src/nsterm.m (ns_term_init): Remove unnecessary call to file-readable that merely introduced a race. * src/process.c, src/sysdep.c, src/term.c: All uses of '#ifdef O_NONBLOCK' changed to '#if O_NONBLOCK', to accommodate gnulib O_* style, and similarly for the other O_* flags. * src/w32.c (sys_faccessat): Rename from sys_access and switch to faccessat's API. All uses changed. * src/xrdb.c: Do not include <sys/stat.h>; no longer needed. (magic_db): Rename from magic_file_p. (magic_db, search_magic_path): Return an XrmDatabase rather than a char *, so that we don't have to test for file existence separately from opening the file for reading. This removes a race fixes a permission-checking problem, and simplifies the code. All uses changed. (file_p): Remove; no longer needed. Fixes: debbugs:12632
2012-11-14 04:55:41 +00:00
/* euidaccess -- check if effective user id can access file
Copyright (C) 1990-1991, 1995, 1998, 2000, 2003-2006, 2008-2017 Free
Use faccessat, not access, when checking file permissions. This fixes a bug that has been present in Emacs since its creation. It was reported by Chris Torek in 1983 even before GNU Emacs existed, which must set some sort of record. (Torek's bug report was against a predecessor of GNU Emacs, but GNU Emacs happened to have the same common flaw.) See Torek's Usenet posting "setuid/setgid programs & Emacs" Article-I.D.: sri-arpa.858 Posted: Fri Apr 8 14:18:56 1983. * .bzrignore: Add lib/fcntl.h. * configure.ac (euidaccess): Remove check; gnulib does this for us now. (gl_FCNTL_O_FLAGS): Define a dummy version. * lib/at-func.c, lib/euidaccess.c, lib/faccessat.c, lib/fcntl.in.h: * lib/getgroups.c, lib/group-member.c, lib/root-uid.h: * lib/xalloc-oversized.h, m4/euidaccess.m4, m4/faccessat.m4: * m4/fcntl_h.m4, m4/getgroups.m4, m4/group-member.m4: New files, from gnulib. * lib/gnulib.mk, m4/gnulib-comp.m4: Regenerate. * admin/merge-gnulib (GNULIB_MODULES): Add faccessat. (GNULIB_TOOL_FLAGS): Avoid at-internal, fchdir, malloc-posix, openat-die, openat-h, save-cwd. Do not avoid fcntl-h. Omit gnulib's m4/fcntl-o.m4. * nt/inc/ms-w32.h (AT_FDCWD, AT_EACCESS): New symbols. (access): Remove. (faccessat): New macro. * src/Makefile.in (LIB_EACCESS): New macro. (LIBES): Use it. * src/callproc.c (init_callproc): * src/charset.c (init_charset): * src/fileio.c (check_existing, check_executable, check_writable) (Ffile_readable_p): * src/lread.c (openp, load_path_check): * src/process.c (allocate_pty): * src/xrdb.c (file_p): Use effective UID when checking permissions, not real UID. * src/callproc.c (init_callproc): * src/charset.c (init_charset): * src/lread.c (load_path_check, init_lread): Test whether directories are accessible, not merely whether they exist. * src/conf_post.h (GNULIB_SUPPORT_ONLY_AT_FDCWD): New macro. * src/fileio.c (check_existing, check_executable, check_writable) (Ffile_readable_p): Use symbolic names instead of integers for the flags, as they're portable now. (check_writable): New arg AMODE. All uses changed. Set errno on failure. (Ffile_readable_p): Use faccessat, not stat + open + close. (Ffile_writable_p): No need to call check_existing + check_writable. Just call check_writable and then look at errno. This saves a syscall. dir should never be nil; replace an unnecessary runtime check with an eassert. When checking the parent directory of a nonexistent file, check that the directory is searchable as well as writable, as we can't create files in unsearchable directories. (file_directory_p): New function, which uses 'stat' on most platforms but faccessat with D_OK (for efficiency) if WINDOWSNT. (Ffile_directory_p, Fset_file_times): Use it. (file_accessible_directory_p): New function, which uses a single syscall for efficiency. (Ffile_accessible_directory_p): Use it. * src/xrdb.c (file_p): Use file_directory_p. * src/lisp.h (file_directory_p, file_accessible_directory_p): New decls. * src/lread.c (openp): When opening a file, use fstat rather than stat, as that avoids a permissions race. When not opening a file, use file_directory_p rather than stat. (dir_warning): First arg is now a usage string, not a format. Use errno. All uses changed. * src/nsterm.m (ns_term_init): Remove unnecessary call to file-readable that merely introduced a race. * src/process.c, src/sysdep.c, src/term.c: All uses of '#ifdef O_NONBLOCK' changed to '#if O_NONBLOCK', to accommodate gnulib O_* style, and similarly for the other O_* flags. * src/w32.c (sys_faccessat): Rename from sys_access and switch to faccessat's API. All uses changed. * src/xrdb.c: Do not include <sys/stat.h>; no longer needed. (magic_db): Rename from magic_file_p. (magic_db, search_magic_path): Return an XrmDatabase rather than a char *, so that we don't have to test for file existence separately from opening the file for reading. This removes a race fixes a permission-checking problem, and simplifies the code. All uses changed. (file_p): Remove; no longer needed. Fixes: debbugs:12632
2012-11-14 04:55:41 +00:00
Software Foundation, Inc.
This file is part of the GNU C Library.
This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 3 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>. */
/* Written by David MacKenzie and Torbjorn Granlund.
Adapted for GNU C library by Roland McGrath. */
#ifndef _LIBC
# include <config.h>
#endif
#include <fcntl.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>
#include "root-uid.h"
#if HAVE_LIBGEN_H
# include <libgen.h>
#endif
#include <errno.h>
#ifndef __set_errno
# define __set_errno(val) errno = (val)
#endif
#if defined EACCES && !defined EACCESS
# define EACCESS EACCES
#endif
#ifndef F_OK
# define F_OK 0
# define X_OK 1
# define W_OK 2
# define R_OK 4
#endif
#ifdef _LIBC
# define access __access
# define getuid __getuid
# define getgid __getgid
# define geteuid __geteuid
# define getegid __getegid
# define group_member __group_member
# define euidaccess __euidaccess
# undef stat
# define stat stat64
#endif
/* Return 0 if the user has permission of type MODE on FILE;
otherwise, return -1 and set 'errno'.
Like access, except that it uses the effective user and group
id's instead of the real ones, and it does not always check for read-only
file system, text busy, etc. */
int
euidaccess (const char *file, int mode)
{
#if HAVE_FACCESSAT /* glibc, AIX 7, Solaris 11, Cygwin 1.7 */
return faccessat (AT_FDCWD, file, mode, AT_EACCESS);
#elif defined EFF_ONLY_OK /* IRIX, OSF/1, Interix */
return access (file, mode | EFF_ONLY_OK);
#elif defined ACC_SELF /* AIX */
return accessx (file, mode, ACC_SELF);
#elif HAVE_EACCESS /* FreeBSD */
return eaccess (file, mode);
#else /* Mac OS X, NetBSD, OpenBSD, HP-UX, Solaris, Cygwin, mingw, BeOS */
uid_t uid = getuid ();
gid_t gid = getgid ();
uid_t euid = geteuid ();
gid_t egid = getegid ();
struct stat stats;
# if HAVE_DECL_SETREGID && PREFER_NONREENTRANT_EUIDACCESS
/* Define PREFER_NONREENTRANT_EUIDACCESS if you prefer euidaccess to
return the correct result even if this would make it
nonreentrant. Define this only if your entire application is
safe even if the uid or gid might temporarily change. If your
application uses signal handlers or threads it is probably not
safe. */
if (mode == F_OK)
return stat (file, &stats);
else
{
int result;
int saved_errno;
if (uid != euid)
setreuid (euid, uid);
if (gid != egid)
setregid (egid, gid);
result = access (file, mode);
saved_errno = errno;
/* Restore them. */
if (uid != euid)
setreuid (uid, euid);
if (gid != egid)
setregid (gid, egid);
errno = saved_errno;
return result;
}
# else
/* The following code assumes the traditional Unix model, and is not
correct on systems that have ACLs or the like. However, it's
better than nothing, and it is reentrant. */
unsigned int granted;
if (uid == euid && gid == egid)
/* If we are not set-uid or set-gid, access does the same. */
return access (file, mode);
if (stat (file, &stats) != 0)
return -1;
/* The super-user can read and write any file, and execute any file
that anyone can execute. */
if (euid == ROOT_UID
&& ((mode & X_OK) == 0
|| (stats.st_mode & (S_IXUSR | S_IXGRP | S_IXOTH))))
return 0;
/* Convert the mode to traditional form, clearing any bogus bits. */
if (R_OK == 4 && W_OK == 2 && X_OK == 1 && F_OK == 0)
mode &= 7;
else
mode = ((mode & R_OK ? 4 : 0)
+ (mode & W_OK ? 2 : 0)
+ (mode & X_OK ? 1 : 0));
if (mode == 0)
return 0; /* The file exists. */
/* Convert the file's permission bits to traditional form. */
if (S_IRUSR == (4 << 6) && S_IWUSR == (2 << 6) && S_IXUSR == (1 << 6)
&& S_IRGRP == (4 << 3) && S_IWGRP == (2 << 3) && S_IXGRP == (1 << 3)
&& S_IROTH == (4 << 0) && S_IWOTH == (2 << 0) && S_IXOTH == (1 << 0))
granted = stats.st_mode;
else
granted = ((stats.st_mode & S_IRUSR ? 4 << 6 : 0)
+ (stats.st_mode & S_IWUSR ? 2 << 6 : 0)
+ (stats.st_mode & S_IXUSR ? 1 << 6 : 0)
+ (stats.st_mode & S_IRGRP ? 4 << 3 : 0)
+ (stats.st_mode & S_IWGRP ? 2 << 3 : 0)
+ (stats.st_mode & S_IXGRP ? 1 << 3 : 0)
+ (stats.st_mode & S_IROTH ? 4 << 0 : 0)
+ (stats.st_mode & S_IWOTH ? 2 << 0 : 0)
+ (stats.st_mode & S_IXOTH ? 1 << 0 : 0));
if (euid == stats.st_uid)
granted >>= 6;
else if (egid == stats.st_gid || group_member (stats.st_gid))
granted >>= 3;
if ((mode & ~granted) == 0)
return 0;
__set_errno (EACCESS);
return -1;
# endif
#endif
}
#undef euidaccess
#ifdef weak_alias
weak_alias (__euidaccess, euidaccess)
#endif
#ifdef TEST
# include <error.h>
# include <stdio.h>
# include <stdlib.h>
int
main (int argc, char **argv)
{
char *file;
int mode;
int err;
if (argc < 3)
abort ();
file = argv[1];
mode = atoi (argv[2]);
err = euidaccess (file, mode);
printf ("%d\n", err);
if (err != 0)
error (0, errno, "%s", file);
exit (0);
}
#endif