linux-kernel - [parch 2/4] vfs: utimensat(): be consistent with utime() for immutable and append-only files

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Date:	Wed, 04 Jun 2008 00:25:01 +0200
From:	Michael Kerrisk <mtk.manpages@...glemail.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
CC:	lkml <linux-kernel@...r.kernel.org>,
	Christoph Hellwig <hch@....de>,
	Miklos Szeredi <miklos@...redi.hu>,
	Al Viro <viro@...iv.linux.org.uk>, jamie@...reable.org,
	Ulrich Drepper <drepper@...hat.com>,
	linux-fsdevel@...r.kernel.org,
	Subrata Modak <subrata@...ux.vnet.ibm.com>
Subject: [parch 2/4] vfs: utimensat(): be consistent with utime() for immutable
 and append-only files

This patch fixes utimensat() to make its behavior consistent
with that of utime()/utimes() when dealing with files marked
immutable and append-only.

The current utimensat() implementation also returns EPERM if
'times' is non-NULL and the tv_nsec fields are both UTIME_NOW.
For consistency, the

(times != NULL && times[0].tv_nsec == UTIME_NOW &&
                  times[1].tv_nsec == UTIME_NOW)

case should be treated like the traditional utimes() case where
'times' is NULL.  That is, the call should succeed for a file
marked append-only and should give the error EACCES if the file
is marked as immutable.

The simple way to do this is to set 'times' to NULL
if (times[0].tv_nsec == UTIME_NOW && times[1].tv_nsec == UTIME_NOW).

This is also the natural approach, since POSIX.1 semantics consider the
times == {{x, UTIME_NOW}, {y, UTIME_NOW}}
to be exactly equivalent to the case for
times == NULL.

(Thanks to Miklos for pointing this out.)

Patch 3 in this series relies on the simplification provided
by this patch.

CC: Miklos Szeredi <miklos@...redi.hu>
CC: Al Viro <viro@...iv.linux.org.uk>
CC: Ulrich Drepper <drepper@...hat.com>
Signed-off-by: Michael Kerrisk <mtk.manpages@...il.com>

--- linux-2.6.26-rc4/fs/utimes.c	2008-06-03 22:47:07.000000000 +0200
+++ linux-2.6.26-rc4-utimensat-fix-v4/fs/utimes.c	2008-06-03 22:59:55.000000000 +0200
@@ -102,6 +102,10 @@
 	if (error)
 		goto dput_and_out;

+	if (times && times[0].tv_nsec == UTIME_NOW &&
+		     times[1].tv_nsec == UTIME_NOW)
+		times = NULL;
+
 	/* Don't worry, the checks are done in inode_change_ok() */
 	newattrs.ia_valid = ATTR_CTIME | ATTR_MTIME | ATTR_ATIME;
 	if (times) {

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