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From: Dave Hansen <hansendc@us.ibm.com>
To: linux-kernel@vger.kernel.org
Cc: akpm@osdl.org, hch@infradead.org, Dave Hansen <hansendc@us.ibm.com>
Subject: [PATCH 12/22] elevate write count files are open()ed
Date: Fri, 09 Feb 2007 14:53:37 -0800	[thread overview]
Message-ID: <20070209225337.C8EC7257@localhost.localdomain> (raw)
In-Reply-To: <20070209225329.27619A62@localhost.localdomain>



This is the first really tricky patch in the series.  It
elevates the writer count on a mount each time a
non-special file is opened for write.

This is not completely apparent in the patch because the
two if() conditions in may_open() above the
mnt_want_write() call are, combined, equivalent to
special_file().

There is also an elevated count around the vfs_create()
call in open_namei().  The count needs to be kept elevated
all the way into the may_open() call.  Otherwise, when the
write is dropped, a ro->rw transisition could occur.  This
would lead to having rw access on the newly created file,
while the vfsmount is ro.  That is bad.

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

 lxc-dave/fs/file_table.c |    5 ++++-
 lxc-dave/fs/namei.c      |   22 ++++++++++++++++++----
 lxc-dave/ipc/mqueue.c    |    3 +++
 3 files changed, 25 insertions(+), 5 deletions(-)

diff -puN fs/file_table.c~14-24-tricky-elevate-write-count-files-are-open-ed fs/file_table.c
--- lxc/fs/file_table.c~14-24-tricky-elevate-write-count-files-are-open-ed	2007-02-09 14:26:54.000000000 -0800
+++ lxc-dave/fs/file_table.c	2007-02-09 14:26:54.000000000 -0800
@@ -209,8 +209,11 @@ void fastcall __fput(struct file *file)
 	if (unlikely(S_ISCHR(inode->i_mode) && inode->i_cdev != NULL))
 		cdev_put(inode->i_cdev);
 	fops_put(file->f_op);
-	if (file->f_mode & FMODE_WRITE)
+	if (file->f_mode & FMODE_WRITE) {
 		put_write_access(inode);
+		if(!special_file(inode->i_mode))
+			mnt_drop_write(mnt);
+	}
 	put_pid(file->f_owner.pid);
 	put_user_ns(file->f_owner.user_ns);
 	file_kill(file);
diff -puN fs/namei.c~14-24-tricky-elevate-write-count-files-are-open-ed fs/namei.c
--- lxc/fs/namei.c~14-24-tricky-elevate-write-count-files-are-open-ed	2007-02-09 14:26:54.000000000 -0800
+++ lxc-dave/fs/namei.c	2007-02-09 14:26:54.000000000 -0800
@@ -1548,8 +1548,17 @@ int may_open(struct nameidata *nd, int a
 			return -EACCES;
 
 		flag &= ~O_TRUNC;
-	} else if (IS_RDONLY(inode) && (flag & FMODE_WRITE))
-		return -EROFS;
+	} else if (flag & FMODE_WRITE) {
+		/*
+		 * effectively: !special_file()
+		 * balanced by __fput()
+		 */
+		error = mnt_want_write(nd->mnt);
+		if (error)
+			return error;
+		if (IS_RDONLY(inode))
+			return -EROFS;
+	}
 	/*
 	 * An append-only file must be opened in append mode for writing.
 	 */
@@ -1688,14 +1697,17 @@ do_last:
 	}
 
 	if (IS_ERR(nd->intent.open.file)) {
-		mutex_unlock(&dir->d_inode->i_mutex);
 		error = PTR_ERR(nd->intent.open.file);
-		goto exit_dput;
+		goto exit_mutex_unlock;
 	}
 
 	/* Negative dentry, just create the file */
 	if (!path.dentry->d_inode) {
+		error = mnt_want_write(nd->mnt);
+		if (error)
+			goto exit_mutex_unlock;
 		error = open_namei_create(nd, &path, flag, mode);
+		mnt_drop_write(nd->mnt);
 		if (error)
 			goto exit;
 		return 0;
@@ -1733,6 +1745,8 @@ ok:
 		goto exit;
 	return 0;
 
+exit_mutex_unlock:
+	mutex_unlock(&dir->d_inode->i_mutex);
 exit_dput:
 	dput_path(&path, nd);
 exit:
diff -puN ipc/mqueue.c~14-24-tricky-elevate-write-count-files-are-open-ed ipc/mqueue.c
--- lxc/ipc/mqueue.c~14-24-tricky-elevate-write-count-files-are-open-ed	2007-02-09 14:26:54.000000000 -0800
+++ lxc-dave/ipc/mqueue.c	2007-02-09 14:26:54.000000000 -0800
@@ -687,6 +687,9 @@ asmlinkage long sys_mq_open(const char _
 				goto out;
 			filp = do_open(dentry, oflag);
 		} else {
+			error = mnt_want_write(mqueue_mnt);
+			if (error)
+				goto out;
 			filp = do_create(mqueue_mnt->mnt_root, dentry,
 						oflag, mode, u_attr);
 		}
_

  parent reply	other threads:[~2007-02-09 22:55 UTC|newest]

Thread overview: 33+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2007-02-09 22:53 [PATCH 01/22] filesystem helpers for custom 'struct file's Dave Hansen
2007-02-09 22:53 ` [PATCH 02/22] r/o bind mounts: add vfsmount writer counts Dave Hansen
2007-02-09 23:41   ` Eric Dumazet
2007-02-10  0:10     ` Dave Hansen
2007-02-09 22:53 ` [PATCH 03/22] record when sb_writer_count elevated for inode Dave Hansen
2007-02-09 22:53 ` [PATCH 04/22] elevate writer count for chown and friends Dave Hansen
2007-02-09 22:53 ` [PATCH 05/22] elevate mnt writers for callers of vfs_mkdir() Dave Hansen
2007-02-09 22:53 ` [PATCH 06/22] elevate write count during entire ncp_ioctl() Dave Hansen
2007-02-09 22:53 ` [PATCH 07/22] elevate write count for link and symlink calls Dave Hansen
2007-02-09 22:53 ` [PATCH 08/22] elevate mount count for extended attributes Dave Hansen
2007-02-09 22:53 ` [PATCH 09/22] mount_is_safe(): add comment Dave Hansen
2007-02-09 22:53 ` [PATCH 10/22] unix_find_other() elevate write count for touch_atime() Dave Hansen
2007-02-09 22:53 ` Dave Hansen [this message]
2007-02-13  5:11   ` [PATCH 12/22] elevate write count files are open()ed Andrew Morton
2007-02-13 16:58     ` Dave Hansen
2007-02-13 17:58       ` Andrew Morton
2007-02-14  0:17         ` Dave Hansen
2007-02-09 22:53 ` [PATCH 11/22] elevate write count over calls to vfs_rename() Dave Hansen
2007-02-09 22:53 ` [PATCH 13/22] elevate writer count for do_sys_truncate() Dave Hansen
2007-02-09 22:53 ` [PATCH 14/22] elevate write count for do_utimes() Dave Hansen
2007-02-09 22:53 ` [PATCH 15/22] elevate write count for do_sys_utime() and touch_atime() Dave Hansen
2007-02-09 22:53 ` [PATCH 16/22] sys_mknodat(): elevate write count for vfs_mknod/create() Dave Hansen
2007-02-09 22:53 ` [PATCH 17/22] elevate mnt writers for vfs_unlink() callers Dave Hansen
2007-02-09 22:53 ` [PATCH 18/22] do_rmdir(): elevate write count Dave Hansen
2007-02-09 22:53 ` [PATCH 19/22] elevate writer count for custom struct_file Dave Hansen
2007-02-09 22:53 ` [PATCH 20/22] [PATCH] gfs: check nlink count Dave Hansen
2007-02-09 22:53 ` [PATCH 21/22] honor r/w changes at do_remount() time Dave Hansen
2007-02-09 23:22   ` Andrew Morton
2007-02-10  0:00     ` Dave Hansen
2007-02-10  0:29     ` Anton Altaparmakov
2007-02-10  9:54     ` Jan Engelhardt
2007-02-09 22:53 ` [PATCH 22/22] kill open files traverse on remount ro Dave Hansen
2007-02-09 23:18 ` [PATCH 01/22] filesystem helpers for custom 'struct file's Andrew Morton

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