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, 8 insertions, 3 deletions

diff --git a/lisp/net/tramp-sh.el b/lisp/net/tramp-sh.el
index 55af0f0d96b..3008601d9ca 100644
--- a/lisp/net/tramp-sh.el
+++ b/lisp/net/tramp-sh.el
@@ -1616,7 +1616,7 @@ and gid of the corresponding user is taken.  Both parameters must be integers."
 	(and (tramp-run-test "-d" (file-name-directory filename))
 	     (tramp-run-test "-w" (file-name-directory filename)))))))
 
-(defun tramp-sh-handle-file-ownership-preserved-p (filename)
+(defun tramp-sh-handle-file-ownership-preserved-p (filename &optional group)
   "Like `file-ownership-preserved-p' for Tramp files."
   (with-parsed-tramp-file-name filename nil
     (with-tramp-file-property v localname "file-ownership-preserved-p"
@@ -1624,7 +1624,10 @@ and gid of the corresponding user is taken.  Both parameters must be integers."
 	;; Return t if the file doesn't exist, since it's true that no
 	;; information would be lost by an (attempted) delete and create.
 	(or (null attributes)
-	    (= (nth 2 attributes) (tramp-get-remote-uid v 'integer)))))))
+	    (and
+	     (= (nth 2 attributes) (tramp-get-remote-uid v 'integer))
+	     (or (not group)
+		 (= (nth 3 attributes) (tramp-get-remote-gid v 'integer)))))))))
 
 ;; Directory listings.
 
@@ -5021,7 +5024,9 @@ This is used internally by `tramp-file-mode-from-int'."
   (if (equal id-format 'integer) (user-uid) (user-login-name)))
 
 (defun tramp-get-local-gid (id-format)
-  (nth 3 (tramp-compat-file-attributes "~/" id-format)))
+  (if (and (fboundp 'group-gid) (equal id-format 'integer))
+      (tramp-compat-funcall 'group-gid)
+    (nth 3 (tramp-compat-file-attributes "~/" id-format))))
 
 ;; Some predefined connection properties.
 (defun tramp-get-inline-compress (vec prop size)