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backup-by-copying-when-privileged-mismatch should apply to gid, too
From: |
Stephen Gildea |
Subject: |
backup-by-copying-when-privileged-mismatch should apply to gid, too |
Date: |
Fri, 20 Dec 2019 09:20:01 -0800 |
I propose to have backup-by-copying-when-privileged-mismatch, which
preserves the ownership of files with low-uid owner (e.g., root-owned
system files), also preserve the ownership of files with low-gid group.
I think failing to look at the file's group was an oversight when we
implemented backup-by-copying-when-privileged-mismatch. Are there any
objections to my fixing it now?
My proposed change is attached:
>From e7aad688807f89532b1e6f2d67e6589c9f740859 Mon Sep 17 00:00:00 2001
From: Stephen Gildea <address@hidden>
Date: Fri, 20 Dec 2019 09:15:13 -0800
Subject: [PATCH] backup-by-copying-when-privileged-mismatch applies to file
gid, too.
* lisp/files.el (backup-by-copying-when-privileged-mismatch): In addition
to checking the file uid, a second test is added: if the file gid is not
greater than backup-by-copying-when-privileged-mismatch,
backup-by-copying-when-mismatch will also be forced on.
* doc/emacs/files.texi, doc/lispref/backups.texi: Updated documentation.
Also fixed a typo in the Emacs reference manual, changing "higher" to
"no greater" so that the limit is no longer documented reversed.
---
doc/emacs/files.texi | 5 +++--
doc/lispref/backups.texi | 6 +++---
etc/NEWS | 5 +++++
lisp/files.el | 15 +++++++++------
4 files changed, 20 insertions(+), 11 deletions(-)
diff --git a/lisp/files.el b/lisp/files.el
index a384e7136e..96f1e8d47e 100644
--- a/lisp/files.el
+++ b/lisp/files.el
@@ -134,10 +134,11 @@ backup-by-copying-when-mismatch
(defcustom backup-by-copying-when-privileged-mismatch 200
"Non-nil means create backups by copying to preserve a privileged owner.
Renaming may still be used (subject to control of other variables)
-when it would not result in changing the owner of the file or if the owner
-has a user id greater than the value of this variable. This is useful
-when low-numbered uid's are used for special system users (such as root)
-that must maintain ownership of certain files.
+when it would not result in changing the owner of the file or if the
+user id and group id of the file are both greater than the value of
+this variable. This is useful when low-numbered uid's and gid's are
+used for special system users (such as root) that must maintain
+ownership of certain files.
This variable is relevant only if `backup-by-copying' and
`backup-by-copying-when-mismatch' are nil."
:type '(choice (const nil) integer)
@@ -4634,8 +4635,10 @@ backup-buffer
(let ((attr (file-attributes
real-file-name
'integer)))
- (<= (file-attribute-user-id attr)
- copy-when-priv-mismatch))))
+ (or (<= (file-attribute-user-id attr)
+ copy-when-priv-mismatch)
+ (<= (file-attribute-group-id attr)
+ copy-when-priv-mismatch)))))
(not (file-ownership-preserved-p real-file-name
t)))))
setmodes)
diff --git a/doc/emacs/files.texi b/doc/emacs/files.texi
index 7221edcc1b..f5dd408cc9 100644
--- a/doc/emacs/files.texi
+++ b/doc/emacs/files.texi
@@ -690,8 +690,9 @@ Backup Copying
the file's owner or group, use copying.
If you change @code{backup-by-copying-when-mismatch} to @code{nil},
-Emacs checks the numeric user-id of the file's owner. If this is
-higher than @code{backup-by-copying-when-privileged-mismatch}, then it
+Emacs checks the numeric user-id of the file's owner and the numeric
+group-id of the file's group. If either is
+no greater than @code{backup-by-copying-when-privileged-mismatch}, then it
behaves as though @code{backup-by-copying-when-mismatch} is
non-@code{nil} anyway.
diff --git a/doc/lispref/backups.texi b/doc/lispref/backups.texi
index 6a5b6d1661..c17d98eb19 100644
--- a/doc/lispref/backups.texi
+++ b/doc/lispref/backups.texi
@@ -232,11 +232,11 @@ Rename or Copy
@defopt backup-by-copying-when-privileged-mismatch
This variable, if non-@code{nil}, specifies the same behavior as
@code{backup-by-copying-when-mismatch}, but only for certain user-id
-values: namely, those less than or equal to a certain number. You set
-this variable to that number.
+and group-id values: namely, those less than or equal to a certain number.
+You set this variable to that number.
Thus, if you set @code{backup-by-copying-when-privileged-mismatch}
-to 0, backup by copying is done for the superuser only,
+to 0, backup by copying is done for the superuser and group 0 only,
when necessary to prevent a change in the owner of the file.
The default is 200.
diff --git a/etc/NEWS b/etc/NEWS
index cf4e705a52..00ba11d94a 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -533,7 +533,11 @@ The HIST argument of 'read-from-minibuffer' now works
correctly with
buffer-local variables. This means that different buffers can have
their own separated input history list if desired.
+** 'backup-by-copying-when-privileged-mismatch' applies to file gid, too.
+In addition to checking the file owner uid, Emacs also checks that the
+group gid is not greater than backup-by-copying-when-privileged-mismatch;
+if so, backup-by-copying-when-mismatch will be forced on.
+
* Editing Changes in Emacs 27.1
--
2.17.1
- backup-by-copying-when-privileged-mismatch should apply to gid, too,
Stephen Gildea <=