Update from Gnulib by running admin/merge-gnulib

* admin/merge-gnulib (AVOIDED_MODULES): Add chmod.

1 files changed, 20 insertions, 39 deletions

diff --git a/lib/fchmodat.c b/lib/fchmodat.c
index dc535833660..164e2c4a95f 100644
--- a/lib/fchmodat.c
+++ b/lib/fchmodat.c
@@ -83,9 +83,10 @@ 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 HAVE_READLINKAT
+      char readlink_buf[1];
 
-#  if defined O_PATH && defined AT_EMPTY_PATH
+#   ifdef O_PATH
       /* 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.
@@ -94,49 +95,29 @@ fchmodat (int dir, char const *file, mode_t mode, int flags)
       if (fd < 0)
         return fd;
 
-      /* 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 undesired - 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)
+      int err;
+      if (0 <= readlinkat (fd, "", readlink_buf, sizeof readlink_buf))
+        err = EOPNOTSUPP;
+      else if (errno == EINVAL)
         {
-          int stat_errno = errno;
-          close (fd);
-          errno = stat_errno;
-          return -1;
-        }
-      if (S_ISLNK (st.st_mode))
-        {
-          close (fd);
-          errno = EOPNOTSUPP;
-          return -1;
+          static char const fmt[] = "/proc/self/fd/%d";
+          char buf[sizeof fmt - sizeof "%d" + INT_BUFSIZE_BOUND (int)];
+          sprintf (buf, fmt, fd);
+          err = chmod (buf, mode) == 0 ? 0 : errno == ENOENT ? -1 : errno;
         }
+      else
+        err = errno == ENOENT ? -1 : errno;
 
-#   if defined __linux__ || defined __ANDROID__ || defined __CYGWIN__
-      static char const fmt[] = "/proc/self/fd/%d";
-      char buf[sizeof fmt - sizeof "%d" + INT_BUFSIZE_BOUND (int)];
-      sprintf (buf, fmt, fd);
-      int chmod_result = chmod (buf, mode);
-      int chmod_errno = errno;
       close (fd);
-      if (chmod_result == 0)
-        return chmod_result;
-      if (chmod_errno != ENOENT)
-        {
-          errno = chmod_errno;
-          return chmod_result;
-        }
+
+      errno = err;
+      if (0 <= err)
+        return err == 0 ? 0 : -1;
 #   endif
-      /* /proc is not mounted or would not work as in GNU/Linux.  */
 
-#  else
-      int fstatat_result = fstatat (dir, file, &st, AT_SYMLINK_NOFOLLOW);
-      if (fstatat_result != 0)
-        return fstatat_result;
-      if (S_ISLNK (st.st_mode))
+      /* O_PATH + /proc is not supported.  */
+
+      if (0 <= readlinkat (dir, file, readlink_buf, sizeof readlink_buf))
         {
           errno = EOPNOTSUPP;
           return -1;