Fix permissions bugs with setgid directories etc.

* configure.ac (BSD4_2): Remove; no longer needed.
* admin/CPP-DEFINES (BSD4_2): Remove.
* doc/lispintro/emacs-lisp-intro.texi (Files List):
directory-files-and-attributes now outputs t for attribute that's
now a placeholder.
* doc/lispref/files.texi (Testing Accessibility): Document GROUP arg
of file-ownership-preserved-p.
(File Attributes): Document that 9th element is now
just a placeholder.
* doc/lispref/os.texi (User Identification): Document new functions group-gid,
group-real-gid.
* etc/NEWS: Document changes to file-attributes,
file-ownership-preserved-p.
Mention new functions group-gid, group-real-gid.
* lisp/files.el (backup-buffer): Don't rely on 9th output of
file-attributes, as it's now a placeholder.  Instead, use the new
optional arg of file-ownership-preserved-p.
(file-ownership-preserved-p): New optional arg GROUP.
Fix mishandling of setuid directories that would cause this
function to return t when it should have returned nil.
Document what happens if the file does not exist, and when
it's not known whether the ownership will be preserved.
* lisp/net/tramp-sh.el (tramp-sh-handle-file-ownership-preserved-p):
Likewise.
(tramp-get-local-gid): Use group-gid for integer, as that's
faster and more reliable.
* src/dired.c (Ffile_attributes): Return t as the 9th attribute,
to mark it as a placeholder.  The old value was often wrong.
The only user of this attribute has been changed to use
file-ownership-preserved-p instead, with its new group arg.
* src/editfns.c (Fgroup_gid, Fgroup_real_gid): New functions.

Fixes: debbugs:13125

1 files changed, 2 insertions, 16 deletions

diff --git a/src/dired.c b/src/dired.c
index 85af906c1da..1fda9e8b371 100644
--- a/src/dired.c
+++ b/src/dired.c
@@ -869,7 +869,7 @@ Elements of the attribute list are:
  7. Size in bytes.
   This is a floating point number if the size is too large for an integer.
  8. File modes, as a string of ten letters or dashes as in ls -l.
- 9. t if file's gid would change if file were deleted and recreated.
+ 9. An unspecified value, present only for backward compatibility.
 10. inode number.  If it is larger than what an Emacs integer can hold,
   this is of the form (HIGH . LOW): first the high bits, then the low 16 bits.
   If even HIGH is too large for an Emacs integer, this is instead of the form
@@ -891,10 +891,6 @@ so last access time will always be midnight of that day.  */)
   Lisp_Object values[12];
   Lisp_Object encoded;
   struct stat s;
-#ifdef BSD4_2
-  Lisp_Object dirname;
-  struct stat sdir;
-#endif /* BSD4_2 */
   int lstat_result;
 
   /* An array to hold the mode string generated by filemodestring,
@@ -974,17 +970,7 @@ so last access time will always be midnight of that day.  */)
 
   filemodestring (&s, modes);
   values[8] = make_string (modes, 10);
-#ifdef BSD4_2 /* file gid will be dir gid */
-  dirname = Ffile_name_directory (filename);
-  if (! NILP (dirname))
-    encoded = ENCODE_FILE (dirname);
-  if (! NILP (dirname) && stat (SDATA (encoded), &sdir) == 0)
-    values[9] = (sdir.st_gid != s.st_gid) ? Qt : Qnil;
-  else                                  /* if we can't tell, assume worst */
-    values[9] = Qt;
-#else                                   /* file gid will be egid */
-  values[9] = (s.st_gid != getegid ()) ? Qt : Qnil;
-#endif  /* not BSD4_2 */
+  values[9] = Qt;
   values[10] = INTEGER_TO_CONS (s.st_ino);
   values[11] = INTEGER_TO_CONS (s.st_dev);