(backup-buffer): Bind local var MODES.

Don't use renaming for a suid or sgid file.
Use backup-buffer-copy to do copying.
(backup-buffer-copy): New subroutine.
Clear suid and sgid bits for the copy.

diff --git a/lisp/files.el b/lisp/files.el
index 4a495aab30c58636983fcfecf2a54e6cb774dc80..6a893d958db54d43056abf6b4c03c80870c77894 100644 (file)
--- a/lisp/files.el
+++ b/lisp/files.el
@@ -2365,12 +2365,15 @@ BACKUPNAME is the backup file name, which is the old file renamed."
                            (or (eq delete-old-versions t) (eq delete-old-versions nil))
                            (or delete-old-versions
                                (y-or-n-p (format "Delete excess backup versions of %s? "
-                                                 real-file-name))))))
+                                                 real-file-name)))))
+                     (modes (file-modes buffer-file-name)))
                  ;; Actually write the back up file.
                  (condition-case ()
                      (if (or file-precious-flag
     ;                        (file-symlink-p buffer-file-name)
                              backup-by-copying
+                             ;; Don't rename a suid or sgid file.
+                             (< 0 (logand modes #o6000))
                              (and backup-by-copying-when-linked
                                   (> (file-nlinks real-file-name) 1))
                              (and (or backup-by-copying-when-mismatch
@@ -2382,19 +2385,10 @@ BACKUPNAME is the backup file name, which is the old file renamed."
                                                   (<= (nth 2 attr) backup-by-copying-when-privileged-mismatch)))
                                          (or (nth 9 attr)
                                              (not (file-ownership-preserved-p real-file-name)))))))
-                         (condition-case ()
-                             (copy-file real-file-name backupname t t)
-                           (file-error
-                            ;; If copying fails because file BACKUPNAME
-                            ;; is not writable, delete that file and try again.
-                            (if (and (file-exists-p backupname)
-                                     (not (file-writable-p backupname)))
-                                (delete-file backupname))
-                            (copy-file real-file-name backupname t t)))
+                         (backup-buffer-copy real-file-name backupname modes)
                        ;; rename-file should delete old backup.
                        (rename-file real-file-name backupname t)
-                       (setq setmodes
-                             (cons (file-modes backupname) backupname)))
+                       (setq setmodes (cons modes backupname)))
                    (file-error
                     ;; If trouble writing the backup, write it in ~.
                     (setq backupname (expand-file-name
@@ -2403,15 +2397,7 @@ BACKUPNAME is the backup file name, which is the old file renamed."
                     (message "Cannot write backup file; backing up in %s"
                              (file-name-nondirectory backupname))
                     (sleep-for 1)
-                    (condition-case ()
-                        (copy-file real-file-name backupname t t)
-                      (file-error
-                       ;; If copying fails because file BACKUPNAME
-                       ;; is not writable, delete that file and try again.
-                       (if (and (file-exists-p backupname)
-                                (not (file-writable-p backupname)))
-                           (delete-file backupname))
-                       (copy-file real-file-name backupname t t)))))
+                    (backup-buffer-copy real-file-name backupname modes)))
                  (setq buffer-backed-up t)
                  ;; Now delete the old versions, if desired.
                  (if delete-old-versions
@@ -2423,6 +2409,18 @@ BACKUPNAME is the backup file name, which is the old file renamed."
                  setmodes)
            (file-error nil))))))
 
+(defun backup-buffer-copy (from-name to-name modes)
+  (condition-case ()
+      (copy-file from-name to-name t t)
+    (file-error
+     ;; If copying fails because file TO-NAME
+     ;; is not writable, delete that file and try again.
+     (if (and (file-exists-p to-name)
+             (not (file-writable-p to-name)))
+        (delete-file to-name))
+     (copy-file from-name to-name t t)))
+  (set-file-modes to-name (logand modes #o1777)))
+
 (defun file-name-sans-versions (name &optional keep-backup-version)
   "Return file NAME sans backup versions or strings.
 This is a separate procedure so your site-init or startup file can