Commit f22bc725 authored by Paul Eggert's avatar Paul Eggert

Don't prevent random file systems from being unmounted.

This fix relies on having the 'fchdir' function, and on having
"." be searchable (or at least readable, on platforms lacking O_SEARCH),
but that's good enough to handle the vast majority of cases and the
remaining folks can just live with the annoyance of file systems
that occasionally can't be unmounted.
* configure.ac (fchdir): New function to check for.
* lib/save-cwd.c: Copy from gnulib, except omit the part that
allocates memory, since that can cause problems in Emacs.
* lib/save-cwd.h: Copy from gnulib.

Fixes: debbugs:18232
parent d5f2feb5
2014-08-10 Paul Eggert <eggert@cs.ucla.edu>
Don't prevent random file systems from being unmounted (Bug#18232).
This fix relies on having the 'fchdir' function, and on having
"." be searchable (or at least readable, on platforms lacking O_SEARCH),
but that's good enough to handle the vast majority of cases and the
remaining folks can just live with the annoyance of file systems
that occasionally can't be unmounted.
* configure.ac (fchdir): New function to check for.
* lib/save-cwd.c: Copy from gnulib, except omit the part that
allocates memory, since that can cause problems in Emacs.
* lib/save-cwd.h: Copy from gnulib.
2014-07-11 Paul Eggert <eggert@cs.ucla.edu>
* Makefile.in (install-arch-indep): Avoid readdir race (Bug#17971).
......
......@@ -3508,7 +3508,7 @@ esac
AC_SUBST(BLESSMAIL_TARGET)
AC_CHECK_FUNCS(accept4 gethostname \
AC_CHECK_FUNCS(accept4 fchdir gethostname \
getrusage get_current_dir_name \
lrand48 \
select getpagesize setlocale \
......
/* save-cwd.c -- Save and restore current working directory.
Copyright (C) 1995, 1997-1998, 2003-2006, 2009-2014 Free Software
Foundation, Inc.
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/>. */
/* Gnulib needs to save and restore the current working directory to
fully emulate functions like fstatat. But Emacs doesn't care what
the current working directory is; it always uses absolute file
names. This module replaces the Gnulib module by omitting the code
that Emacs does not need. */
#include <config.h>
#define SAVE_CWD_INLINE _GL_EXTERN_INLINE
#include "save-cwd.h"
#include <fcntl.h>
#include <unistd.h>
/* Record the location of the current working directory in CWD so that
the program may change to other directories and later use restore_cwd
to return to the recorded location. This function may allocate
space using malloc (via getcwd) or leave a file descriptor open;
use free_cwd to perform the necessary free or close. Upon failure,
no memory is allocated, any locally opened file descriptors are
closed; return non-zero -- in that case, free_cwd need not be
called, but doing so is ok. Otherwise, return zero.
The _raison d'etre_ for this interface is that the working directory
is sometimes inaccessible, and getcwd is not robust or as efficient.
So, we prefer to use the open/fchdir approach, but fall back on
getcwd if necessary. This module works for most cases with just
the getcwd-lgpl module, but to be truly robust, use the getcwd module.
Some systems lack fchdir altogether: e.g., OS/2, pre-2001 Cygwin,
SCO Xenix. Also, SunOS 4 and Irix 5.3 provide the function, yet it
doesn't work for partitions on which auditing is enabled. If
you're still using an obsolete system with these problems, please
send email to the maintainer of this code. */
int
save_cwd (struct saved_cwd *cwd)
{
#ifdef HAVE_FCHDIR
cwd->desc = open (".", O_SEARCH | O_CLOEXEC);
#else
cwd->desc = -1;
#endif
/* The 'name' member is present only to minimize differences from
gnulib. Initialize it to zero, if only to simplify debugging. */
cwd->name = 0;
return 0;
}
/* Change to recorded location, CWD, in directory hierarchy.
Upon failure, return -1 (errno is set by chdir or fchdir).
Upon success, return zero. */
int
restore_cwd (const struct saved_cwd *cwd)
{
#ifdef HAVE_FCHDIR
/* Restore the previous directory if possible, to avoid tying down
the file system of the new directory (Bug#18232). */
if (fchdir (cwd->desc) == 0)
return 0;
/* Don't worry if fchdir fails, as Emacs doesn't care what the
working directory is. The fchdir call is inside an 'if' merely to
pacify compilers that complain if fchdir's return value is ignored. */
#endif
return 0;
}
void
free_cwd (struct saved_cwd *cwd)
{
close (cwd->desc);
}
/* Do not save and restore the current working directory.
/* Save and restore current working directory.
Copyright 2013-2014 Free Software Foundation, Inc.
Copyright (C) 1995, 1997-1998, 2003, 2009-2014 Free Software Foundation,
Inc.
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
......@@ -15,32 +16,19 @@
You should have received a copy of the GNU General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>. */
/* Gnulib needs to save and restore the current working directory to
fully emulate functions like fstatat. But Emacs doesn't care what
the current working directory is; it always uses absolute file
names. This module replaces the Gnulib module by omitting the code
that Emacs does not need. */
/* Written by Jim Meyering. */
#ifndef SAVE_CWD_H
#define SAVE_CWD_H 1
# define SAVE_CWD_H 1
_GL_INLINE_HEADER_BEGIN
#ifndef SAVE_CWD_INLINE
# define SAVE_CWD_INLINE _GL_INLINE
#endif
struct saved_cwd
{
int desc;
char *name;
};
struct saved_cwd { int desc; };
int save_cwd (struct saved_cwd *cwd);
int restore_cwd (const struct saved_cwd *cwd);
void free_cwd (struct saved_cwd *cwd);
SAVE_CWD_INLINE int
save_cwd (struct saved_cwd *cwd)
{
cwd->desc = -1;
return 0;
}
SAVE_CWD_INLINE int restore_cwd (struct saved_cwd const *cwd) { return 0; }
SAVE_CWD_INLINE void free_cwd (struct saved_cwd *cwd) { }
_GL_INLINE_HEADER_END
#endif
#endif /* SAVE_CWD_H */
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