Home » Mailing list archives » linux-kernel » 2008 » February » 15

[PATCH 25/30] r/o bind mounts: make access() use new r/o helper

!MAILaRCHIVE_VOTE_RePLACE
Previous message: [thread] [date] [author]
Next message: [thread] [date] [author]
[view in full thread]
From: Dave Hansen <haveblue@...>
To: <linux-kernel@...>
Cc: <hch@...>, <miklos@...>, <akpm@...>, Dave Hansen <haveblue@...>
Subject: [PATCH 25/30] r/o bind mounts: make access() use new r/o helper
Date: Friday, February 15, 2008 - 6:37 pm

It is OK to let access() go without using a mnt_want/drop_write() pair because
it doesn't actually do writes to the filesystem, and it is inherently racy
anyway.  This is a rare case when it is OK to use __mnt_is_readonly()
directly.

Acked-by: Al Viro <viro@ZenIV.linux.org.uk>
Signed-off-by: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Dave Hansen <haveblue@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 linux-2.6.git-dave/fs/open.c |   13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff -puN fs/open.c~r-o-bind-mounts-make-access-use-mnt-check fs/open.c
--- linux-2.6.git/fs/open.c~r-o-bind-mounts-make-access-use-mnt-check	2008-02-15 13:25:57.000000000 -0800
+++ linux-2.6.git-dave/fs/open.c	2008-02-15 13:25:57.000000000 -0800
@@ -459,8 +459,17 @@ asmlinkage long sys_faccessat(int dfd, c
 	if(res || !(mode & S_IWOTH) ||
 	   special_file(nd.path.dentry->d_inode->i_mode))
 		goto out_path_release;
-
-	if(IS_RDONLY(nd.path.dentry->d_inode))
+	/*
+	 * This is a rare case where using __mnt_is_readonly()
+	 * is OK without a mnt_want/drop_write() pair.  Since
+	 * no actual write to the fs is performed here, we do
+	 * not need to telegraph to that to anyone.
+	 *
+	 * By doing this, we accept that this access is
+	 * inherently racy and know that the fs may change
+	 * state before we even see this result.
+	 */
+	if (__mnt_is_readonly(nd.path.mnt))
 		res = -EROFS;
 
 out_path_release:
_
--
Previous message: [thread] [date] [author]
Next message: [thread] [date] [author]
Messages in current thread:
[PATCH 00/30] Read-only bind mounts (-mm resend), Dave Hansen, (Fri Feb 15, 6:37 pm)
[PATCH] r/o bind mounts: stub functions, Dave Hansen, (Fri Feb 15, 9:32 pm)
[PATCH 30/30] r/o bind mounts: debugging for missed calls, Dave Hansen, (Fri Feb 15, 6:38 pm)
[PATCH 29/30] r/o bind mounts: honor mount writer counts at ..., Dave Hansen, (Fri Feb 15, 6:38 pm)
[PATCH 28/30] r/o bind mounts: track numbers of writers to m..., Dave Hansen, (Fri Feb 15, 6:37 pm)
Re: [PATCH 28/30] r/o bind mounts: track numbers of writers ..., Miklos Szeredi, (Mon Feb 18, 12:10 pm)
Re: [PATCH 28/30] r/o bind mounts: track numbers of writers ..., Dave Hansen, (Wed Feb 20, 5:12 pm)
[PATCH 27/30] r/o bind mounts: get callers of vfs_mknod/crea..., Dave Hansen, (Fri Feb 15, 6:37 pm)
[PATCH 26/30] r/o bind mounts: check mnt instead of superblo..., Dave Hansen, (Fri Feb 15, 6:37 pm)
[PATCH 22/30] r/o bind mounts: elevate write count for chmod..., Dave Hansen, (Fri Feb 15, 6:37 pm)
[PATCH 25/30] r/o bind mounts: make access() use new r/o hel..., Dave Hansen, (Fri Feb 15, 6:37 pm)
[PATCH 24/30] r/o bind mounts: elevate count for xfs timesta..., Dave Hansen, (Fri Feb 15, 6:37 pm)
[PATCH 23/30] r/o bind mounts: write counts for truncate(), Dave Hansen, (Fri Feb 15, 6:37 pm)
[PATCH 21/30] r/o bind mounts: get write access for vfs_rena..., Dave Hansen, (Fri Feb 15, 6:37 pm)
[PATCH 20/30] r/o bind mounts: elevate write count for open()s, Dave Hansen, (Fri Feb 15, 6:37 pm)
[PATCH 19/30] r/o bind mounts: elevate write count for ioctl..., Dave Hansen, (Fri Feb 15, 6:37 pm)
[PATCH 18/30] r/o bind mounts: write counts for link/symlink, Dave Hansen, (Fri Feb 15, 6:37 pm)
[PATCH 17/30] r/o bind mounts: write count for file_update_t..., Dave Hansen, (Fri Feb 15, 6:37 pm)
[PATCH 06/30] merge open_namei() and do_filp_open(), Dave Hansen, (Fri Feb 15, 6:37 pm)
[PATCH 16/30] r/o bind mounts: elevate write count for do_ut..., Dave Hansen, (Fri Feb 15, 6:37 pm)
[PATCH 15/30] r/o bind mounts: write counts for time functions, Dave Hansen, (Fri Feb 15, 6:37 pm)
[PATCH 14/30] r/o bind mounts: elevate write count for ncp_i..., Dave Hansen, (Fri Feb 15, 6:37 pm)
[PATCH 13/30] r/o bind mounts: elevate write count for xattr..., Dave Hansen, (Fri Feb 15, 6:37 pm)
[PATCH 12/30] r/o bind mounts: elevate mnt_writers for unlin..., Dave Hansen, (Fri Feb 15, 6:37 pm)
[PATCH 11/30] r/o bind mounts: elevate write count for calle..., Dave Hansen, (Fri Feb 15, 6:37 pm)
[PATCH 10/30] r/o bind mounts: elevate write count for vfs_r..., Dave Hansen, (Fri Feb 15, 6:37 pm)
[PATCH 08/30] r/o bind mounts: create helper to drop file wr..., Dave Hansen, (Fri Feb 15, 6:37 pm)
[PATCH 05/30] do namei_flags calculation inside open_namei(), Dave Hansen, (Fri Feb 15, 6:37 pm)
[PATCH 03/30] check for null vfsmount in dentry_open(), Dave Hansen, (Fri Feb 15, 6:37 pm)
[PATCH 07/30] r/o bind mounts: stub functions, Dave Hansen, (Fri Feb 15, 6:37 pm)
Re: [PATCH 07/30] r/o bind mounts: stub functions, Theodore Tso, (Fri Feb 15, 8:32 pm)
Re: [PATCH 07/30] r/o bind mounts: stub functions, Dave Hansen, (Fri Feb 15, 8:49 pm)
Re: [PATCH 07/30] r/o bind mounts: stub functions, Theodore Tso, (Fri Feb 15, 9:00 pm)
Re: [PATCH 07/30] r/o bind mounts: stub functions, Andrew Morton, (Fri Feb 15, 9:11 pm)
Re: [PATCH 07/30] r/o bind mounts: stub functions, Christoph Hellwig, (Sat Feb 16, 2:31 am)
Re: [PATCH 07/30] r/o bind mounts: stub functions, Dave Hansen, (Wed Feb 20, 6:25 pm)
Re: [PATCH 07/30] r/o bind mounts: stub functions, Christoph Hellwig, (Wed Feb 20, 6:58 pm)
Re: [PATCH 07/30] r/o bind mounts: stub functions, Andrew Morton, (Sat Feb 16, 2:46 am)
Re: [PATCH 07/30] r/o bind mounts: stub functions, Dave Hansen, (Mon Feb 18, 3:06 am)
[PATCH 09/30] r/o bind mounts: drop write during emergency r..., Dave Hansen, (Fri Feb 15, 6:37 pm)
Re: [PATCH 09/30] r/o bind mounts: drop write during emergen..., Miklos Szeredi, (Mon Feb 18, 12:29 pm)
Re: [PATCH 09/30] r/o bind mounts: drop write during emergen..., Al Viro, (Sat Feb 23, 9:38 am)
[PATCH 01/30] reiserfs: eliminate private use of struct file..., Dave Hansen, (Fri Feb 15, 6:37 pm)
[PATCH 04/30] fix up new filp allocators, Dave Hansen, (Fri Feb 15, 6:37 pm)
[PATCH 02/30] hppfs pass vfsmount to dentry_open(), Dave Hansen, (Fri Feb 15, 6:37 pm)