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[PATCH 02/24] rearrange may_open() to be r/o friendly

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From: Dave Hansen <haveblue@...>
To: <akpm@...>
Cc: <linux-kernel@...>, <hch@...>, Dave Hansen <haveblue@...>
Subject: [PATCH 02/24] rearrange may_open() to be r/o friendly
Date: Monday, September 17, 2007 - 2:27 pm

may_open() calls vfs_permission() before it does checks for
IS_RDONLY(inode).  It checks _again_ inside of vfs_permission().

The check inside of vfs_permission() is going away eventually.
With the mnt_want/drop_write() functions, all of the r/o
checks (except for this one) are consistently done before
calling permission().  Because of this, I'd like to use
permission() to hold a debugging check to make sure that
the mnt_want/drop_write() calls are actually being made.

So, to do this:
1. remove the IS_RDONLY() check from permission()
2. enforce that you must mnt_want_write() before
   even calling permission()
3. enable a debugging in permission()

We need to rearrange may_open().  Here's the patch.

Signed-off-by: Dave Hansen <haveblue@us.ibm.com>
---

 lxc-dave/fs/namei.c |   14 +++++++++-----
 1 file changed, 9 insertions(+), 5 deletions(-)

diff -puN fs/namei.c~rearrange-permission-and-ro-checks-in-may_open fs/namei.c
--- lxc/fs/namei.c~rearrange-permission-and-ro-checks-in-may_open	2007-09-17 09:43:56.000000000 -0700
+++ lxc-dave/fs/namei.c	2007-09-17 09:43:56.000000000 -0700
@@ -228,6 +228,10 @@ int generic_permission(struct inode *ino
 int permission(struct inode *inode, int mask, struct nameidata *nd)
 {
 	int retval, submask;
+	struct vfsmount *mnt = NULL;
+
+	if (nd)
+		mnt = nd->mnt;
 
 	if (mask & MAY_WRITE) {
 		umode_t mode = inode->i_mode;
@@ -251,7 +255,7 @@ int permission(struct inode *inode, int 
 		 * MAY_EXEC on regular files is denied if the fs is mounted
 		 * with the "noexec" flag.
 		 */
-		if (nd && nd->mnt && (nd->mnt->mnt_flags & MNT_NOEXEC))
+		if (mnt && (mnt->mnt_flags & MNT_NOEXEC))
 			return -EACCES;
 	}
 
@@ -1604,10 +1608,6 @@ int may_open(struct nameidata *nd, int a
 	if (S_ISDIR(inode->i_mode) && (flag & FMODE_WRITE))
 		return -EISDIR;
 
-	error = vfs_permission(nd, acc_mode);
-	if (error)
-		return error;
-
 	/*
 	 * FIFO's, sockets and device files are special: they don't
 	 * actually live on the filesystem itself, and as such you
@@ -1622,6 +1622,10 @@ int may_open(struct nameidata *nd, int a
 		flag &= ~O_TRUNC;
 	} else if (IS_RDONLY(inode) && (flag & FMODE_WRITE))
 		return -EROFS;
+
+	error = vfs_permission(nd, acc_mode);
+	if (error)
+		return error;
 	/*
 	 * An append-only file must be opened in append mode for writing.
 	 */
_
-
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Messages in current thread:
[PATCH 00/24] Read-only bind mounts, Dave Hansen, (Mon Sep 17, 2:27 pm)
Re: [PATCH 00/24] Read-only bind mounts, Christoph Hellwig, (Wed Sep 19, 1:44 pm)
Re: [PATCH 00/24] Read-only bind mounts, Andrew Morton, (Wed Sep 19, 5:24 pm)
Re: [PATCH 00/24] Read-only bind mounts, Dave Hansen, (Wed Sep 19, 5:56 pm)
Re: [PATCH 00/24] Read-only bind mounts, Andrew Morton, (Wed Sep 19, 6:06 pm)
Re: [PATCH 00/24] Read-only bind mounts, Miklos Szeredi, (Thu Sep 20, 5:58 am)
Re: [PATCH 00/24] Read-only bind mounts, Serge E. Hallyn, (Wed Sep 19, 10:21 am)
[PATCH 14/24] unix_find_other() elevate write count for touc..., Dave Hansen, (Mon Sep 17, 2:27 pm)
Re: [PATCH 14/24] unix_find_other() elevate write count for ..., Christoph Hellwig, (Wed Sep 19, 1:35 pm)
[PATCH 22/24] do_rmdir(): elevate write count, Dave Hansen, (Mon Sep 17, 2:27 pm)
Re: [PATCH 22/24] do_rmdir(): elevate write count, Christoph Hellwig, (Wed Sep 19, 1:39 pm)
[PATCH 21/24] elevate mnt writers for vfs_unlink() callers, Dave Hansen, (Mon Sep 17, 2:27 pm)
Re: [PATCH 21/24] elevate mnt writers for vfs_unlink() callers, Christoph Hellwig, (Wed Sep 19, 1:38 pm)
[PATCH 19/24] elevate write count for do_sys_utime() and tou..., Dave Hansen, (Mon Sep 17, 2:27 pm)
Re: [PATCH 19/24] elevate write count for do_sys_utime() and..., Christoph Hellwig, (Wed Sep 19, 1:36 pm)
[PATCH 20/24] sys_mknodat(): elevate write count for vfs_mkn..., Dave Hansen, (Mon Sep 17, 2:27 pm)
Re: [PATCH 20/24] sys_mknodat(): elevate write count for vfs..., Christoph Hellwig, (Wed Sep 19, 1:38 pm)
[PATCH 09/24] elevate mnt writers for callers of vfs_mkdir(), Dave Hansen, (Mon Sep 17, 2:27 pm)
Re: [PATCH 09/24] elevate mnt writers for callers of vfs_mkd..., Christoph Hellwig, (Wed Sep 19, 1:32 pm)
[PATCH 04/24] r/o bind mounts: stub functions, Dave Hansen, (Mon Sep 17, 2:27 pm)
Re: [PATCH 04/24] r/o bind mounts: stub functions, Christoph Hellwig, (Wed Sep 19, 1:28 pm)
[PATCH 11/24] elevate write count for link and symlink calls, Dave Hansen, (Mon Sep 17, 2:27 pm)
Re: [PATCH 11/24] elevate write count for link and symlink c..., Christoph Hellwig, (Wed Sep 19, 1:33 pm)
[PATCH 06/24] r/o bind mounts: elevate write count for some ..., Dave Hansen, (Mon Sep 17, 2:27 pm)
Re: [PATCH 06/24] r/o bind mounts: elevate write count for s..., Christoph Hellwig, (Wed Sep 19, 1:31 pm)
[PATCH 18/24] elevate write count for do_utimes(), Dave Hansen, (Mon Sep 17, 2:27 pm)
Re: [PATCH 18/24] elevate write count for do_utimes(), Christoph Hellwig, (Wed Sep 19, 1:36 pm)
[PATCH 16/24] nfs: check mnt instead of superblock directly, Dave Hansen, (Mon Sep 17, 2:27 pm)
Re: [PATCH 16/24] nfs: check mnt instead of superblock direc..., Christoph Hellwig, (Wed Sep 19, 1:36 pm)
[PATCH 17/24] elevate writer count for do_sys_truncate(), Dave Hansen, (Mon Sep 17, 2:27 pm)
Re: [PATCH 17/24] elevate writer count for do_sys_truncate(), Christoph Hellwig, (Wed Sep 19, 1:36 pm)
[PATCH 15/24] elevate write count over calls to vfs_rename(), Dave Hansen, (Mon Sep 17, 2:27 pm)
Re: [PATCH 15/24] elevate write count over calls to vfs_rena..., Christoph Hellwig, (Wed Sep 19, 1:35 pm)
[PATCH 12/24] elevate mount count for extended attributes, Dave Hansen, (Mon Sep 17, 2:27 pm)
Re: [PATCH 12/24] elevate mount count for extended attributes, Christoph Hellwig, (Wed Sep 19, 1:34 pm)
[PATCH 10/24] elevate write count during entire ncp_ioctl(), Dave Hansen, (Mon Sep 17, 2:27 pm)
Re: [PATCH 10/24] elevate write count during entire ncp_ioct..., Christoph Hellwig, (Wed Sep 19, 1:33 pm)
[PATCH 01/24] filesystem helpers for custom 'struct file's, Dave Hansen, (Mon Sep 17, 2:27 pm)
Re: [PATCH 01/24] filesystem helpers for custom 'struct file's, Christoph Hellwig, (Wed Sep 19, 1:26 pm)
[PATCH] docuement filesystem helpers for custom 'struct file's, Dave Hansen, (Wed Sep 19, 1:47 pm)
Re: [PATCH] docuement filesystem helpers for custom 'struct ..., Randy Dunlap, (Wed Sep 19, 6:07 pm)
Re: [PATCH] docuement filesystem helpers for custom 'struct ..., Dave Hansen, (Thu Sep 20, 1:25 pm)
Re: [PATCH] docuement filesystem helpers for custom 'struct ..., Christoph Hellwig, (Thu Sep 20, 1:30 pm)
[PATCH 05/24] elevate write count open()'d files, Dave Hansen, (Mon Sep 17, 2:27 pm)
Re: [PATCH 05/24] elevate write count open()'d files, Christoph Hellwig, (Wed Sep 19, 1:30 pm)
[PATCH 07/24] elevate writer count for chown and friends, Dave Hansen, (Mon Sep 17, 2:27 pm)
Re: [PATCH 07/24] elevate writer count for chown and friends, Christoph Hellwig, (Wed Sep 19, 1:31 pm)
[PATCH 13/24] elevate write count for file_update_time(), Dave Hansen, (Mon Sep 17, 2:27 pm)
Re: [PATCH 13/24] elevate write count for file_update_time(), Christoph Hellwig, (Wed Sep 19, 1:35 pm)
[PATCH 08/24] make access() use mnt check, Dave Hansen, (Mon Sep 17, 2:27 pm)
Re: [PATCH 08/24] make access() use mnt check, Christoph Hellwig, (Wed Sep 19, 1:32 pm)
[PATCH 03/24] create cleanup helper svc_msnfs(), Dave Hansen, (Mon Sep 17, 2:27 pm)
Re: [PATCH 03/24] create cleanup helper svc_msnfs(), Jan Engelhardt, (Wed Sep 19, 1:39 pm)
Re: [PATCH 03/24] create cleanup helper svc_msnfs(), Dave Hansen, (Wed Sep 19, 1:45 pm)
Re: [PATCH 03/24] create cleanup helper svc_msnfs(), Trond Myklebust, (Wed Sep 19, 1:54 pm)
Re: [PATCH 03/24] create cleanup helper svc_msnfs(), Christoph Hellwig, (Wed Sep 19, 1:59 pm)
Re: [PATCH 03/24] create cleanup helper svc_msnfs(), Trond Myklebust, (Wed Sep 19, 2:10 pm)
Re: [PATCH 03/24] create cleanup helper svc_msnfs(), Christoph Hellwig, (Wed Sep 19, 1:28 pm)
[PATCH 02/24] rearrange may_open() to be r/o friendly, Dave Hansen, (Mon Sep 17, 2:27 pm)
Re: [PATCH 02/24] rearrange may_open() to be r/o friendly, Christoph Hellwig, (Wed Sep 19, 1:27 pm)
Re: [PATCH 02/24] rearrange may_open() to be r/o friendly, Dave Hansen, (Thu Sep 20, 2:47 pm)