> > Perhaps lchmod.m4 and fchmodat.m4 should define a symbol
> > HAVE_LCHMOD_BUG_WITH_NON_SYMLINKS and the C code could refer to that.
> 2020-02-16 Bruno Haible <br...@clisp.org>
>
> lchmod: Make more future-proof.
> * m4/lchmod.m4 (gl_FUNC_LCHMOD): Define NEED_LCHMOD_NONSYMLINK_FIX.
> (gl_PREREQ_LCHMOD): New macro.
> * lib/lchmod.c (orig_lchmod): New function.
> (lchmod): Test NEED_LCHMOD_NONSYMLINK_FIX. Access /proc only on Linux.
> Return EOPNOTSUPP only on Linux and on platforms without lchmod
> function.
> * modules/lchmod (configure.ac): Invoke gl_PREREQ_LCHMOD.
And here's a similar change for 'fchmodat'. It has one or two code branches
that currently are dead code, but this is on purpose: this is code that
will becomes active when either the NEED_FCHMODAT_NONSYMLINK_FIX test
will trigger on more platforms, or some more autoconf tests will be added
to fchmodat.m4.
2020-02-16 Bruno Haible <br...@clisp.org>
fchmodat: Make more future-proof.
* m4/fchmodat.m4 (gl_FUNC_FCHMODAT): Define
NEED_FCHMODAT_NONSYMLINK_FIX.
(gl_PREREQ_FCHMODAT): New macro.
* lib/fchmodat.c (fchmodat): Test NEED_FCHMODAT_NONSYMLINK_FIX. Access
/proc only on Linux. Return EOPNOTSUPP only on Linux and on platforms
without lchmod function.
* modules/fchmodat (configure.ac): Invoke gl_PREREQ_FCHMODAT.
>From f4693b0166bab83ab232dcd3cfd95906411d1110 Mon Sep 17 00:00:00 2001
From: Bruno Haible <br...@clisp.org>
Date: Sun, 16 Feb 2020 23:01:08 +0100
Subject: [PATCH] fchmodat: Make more future-proof.
* m4/fchmodat.m4 (gl_FUNC_FCHMODAT): Define
NEED_FCHMODAT_NONSYMLINK_FIX.
(gl_PREREQ_FCHMODAT): New macro.
* lib/fchmodat.c (fchmodat): Test NEED_FCHMODAT_NONSYMLINK_FIX. Access
/proc only on Linux. Return EOPNOTSUPP only on Linux and on platforms
without lchmod function.
* modules/fchmodat (configure.ac): Invoke gl_PREREQ_FCHMODAT.
---
ChangeLog | 11 +++++++++++
lib/fchmodat.c | 30 +++++++++++++++++++++++-------
m4/fchmodat.m4 | 15 +++++++++++++--
modules/fchmodat | 1 +
4 files changed, 48 insertions(+), 9 deletions(-)
diff --git a/ChangeLog b/ChangeLog
index 30cc425..8215147 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,16 @@
2020-02-16 Bruno Haible <br...@clisp.org>
+ fchmodat: Make more future-proof.
+ * m4/fchmodat.m4 (gl_FUNC_FCHMODAT): Define
+ NEED_FCHMODAT_NONSYMLINK_FIX.
+ (gl_PREREQ_FCHMODAT): New macro.
+ * lib/fchmodat.c (fchmodat): Test NEED_FCHMODAT_NONSYMLINK_FIX. Access
+ /proc only on Linux. Return EOPNOTSUPP only on Linux and on platforms
+ without lchmod function.
+ * modules/fchmodat (configure.ac): Invoke gl_PREREQ_FCHMODAT.
+
+2020-02-16 Bruno Haible <br...@clisp.org>
+
lchmod: Make more future-proof.
* m4/lchmod.m4 (gl_FUNC_LCHMOD): Define NEED_LCHMOD_NONSYMLINK_FIX.
(gl_PREREQ_LCHMOD): New macro.
diff --git a/lib/fchmodat.c b/lib/fchmodat.c
index 02e2da9..bb48b44 100644
--- a/lib/fchmodat.c
+++ b/lib/fchmodat.c
@@ -14,7 +14,7 @@
You should have received a copy of the GNU General Public License
along with this program. If not, see <https://www.gnu.org/licenses/>. */
-/* written by Jim Meyering */
+/* written by Jim Meyering and Paul Eggert */
/* If the user's config.h happens to include <sys/stat.h>, let it include only
the system's <sys/stat.h> here, so that orig_fchmodat doesn't recurse to
@@ -63,16 +63,27 @@ orig_fchmodat (int dir, char const *file, mode_t mode, int flags)
int
fchmodat (int dir, char const *file, mode_t mode, int flags)
{
+# if NEED_FCHMODAT_NONSYMLINK_FIX
if (flags == AT_SYMLINK_NOFOLLOW)
{
struct stat st;
-# if defined O_PATH && defined AT_EMPTY_PATH
+# if defined O_PATH && defined AT_EMPTY_PATH \
+ && (defined __linux__ || defined __ANDROID__)
+ /* Open a file descriptor with O_NOFOLLOW, to make sure we don't
+ follow symbolic links, if /proc is mounted. O_PATH is used to
+ avoid a failure if the file is not readable.
+ Cf. <https://sourceware.org/bugzilla/show_bug.cgi?id=14578> */
int fd = openat (dir, file, O_PATH | O_NOFOLLOW | O_CLOEXEC);
if (fd < 0)
return fd;
- /* Use fstatat because fstat does not work on O_PATH descriptors
+ /* Up to Linux 5.3 at least, when FILE refers to a symbolic link, the
+ chmod call below will change the permissions of the symbolic link
+ - which is undersired - and on many file systems (ext4, btrfs, jfs,
+ xfs, ..., but not reiserfs) fail with error EOPNOTSUPP - which is
+ misleading. Therefore test for a symbolic link explicitly.
+ Use fstatat because fstat does not work on O_PATH descriptors
before Linux 3.6. */
if (fstatat (fd, "", &st, AT_EMPTY_PATH) != 0)
{
@@ -102,7 +113,9 @@ fchmodat (int dir, char const *file, mode_t mode, int flags)
return chmod_result;
}
/* /proc is not mounted. */
-# else
+ /* Fall back on orig_fchmodat, despite the race. */
+ return orig_fchmodat (dir, file, mode, 0);
+# elif (defined __linux__ || defined __ANDROID__) || !HAVE_LCHMOD
int fstatat_result = fstatat (dir, file, &st, AT_SYMLINK_NOFOLLOW);
if (fstatat_result != 0)
return fstatat_result;
@@ -111,10 +124,13 @@ fchmodat (int dir, char const *file, mode_t mode, int flags)
errno = EOPNOTSUPP;
return -1;
}
-# endif
- /* Fall back on chmod, despite the race. */
- flags = 0;
+ /* Fall back on orig_fchmodat, despite the race. */
+ return orig_fchmodat (dir, file, mode, 0);
+# else
+ return orig_fchmodat (dir, file, mode, 0);
+# endif
}
+# endif
return orig_fchmodat (dir, file, mode, flags);
}
diff --git a/m4/fchmodat.m4 b/m4/fchmodat.m4
index f284485..e3f2f04 100644
--- a/m4/fchmodat.m4
+++ b/m4/fchmodat.m4
@@ -1,4 +1,4 @@
-# fchmodat.m4 serial 3
+# fchmodat.m4 serial 4
dnl Copyright (C) 2004-2020 Free Software Foundation, Inc.
dnl This file is free software; the Free Software Foundation
dnl gives unlimited permission to copy and/or distribute it,
@@ -65,7 +65,18 @@ AC_DEFUN([gl_FUNC_FCHMODAT],
rm -f conftest.fchmodat])
case $gl_cv_func_fchmodat_works in
*yes) ;;
- *) REPLACE_FCHMODAT=1;;
+ *)
+ AC_DEFINE([NEED_FCHMODAT_NONSYMLINK_FIX], [1],
+ [Define to 1 if fchmodat+AT_SYMLINK_NOFOLLOW does not work right on non-symlinks.])
+ REPLACE_FCHMODAT=1
+ ;;
esac
fi
])
+
+# Prerequisites of lib/fchmodat.c.
+AC_DEFUN([gl_PREREQ_FCHMODAT],
+[
+ AC_CHECK_FUNCS_ONCE([lchmod])
+ :
+])
diff --git a/modules/fchmodat b/modules/fchmodat
index b0f06e8..f0dac9d 100644
--- a/modules/fchmodat
+++ b/modules/fchmodat
@@ -28,6 +28,7 @@ configure.ac:
gl_FUNC_FCHMODAT
if test $HAVE_FCHMODAT = 0 || test $REPLACE_FCHMODAT = 1; then
AC_LIBOBJ([fchmodat])
+ gl_PREREQ_FCHMODAT
fi
gl_MODULE_INDICATOR([fchmodat]) dnl for lib/openat.h
gl_SYS_STAT_MODULE_INDICATOR([fchmodat])
--
2.7.4
