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[PATCH] r/o bind mounts: elevate write count for open()s

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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.

We used to do this in may_open(), but Miklos pointed out that __dentry_open()
is used as well to create filps.  This will cover even those cases, while a
call in may_open() would not have.

There is also an elevated count around the vfs_create() call in open_namei().
See the comments for more details, but we need this to fix a 'create, remount,
fail r/w open()' race.

Some filesystems forego the use of normal vfs calls to create
struct files.   Make sure that these users elevate the mnt
writer count because they will get __fput(), and we need
to make sure they're balanced.

Acked-by: Al Viro <viro@ZenIV.linux.org.uk>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Dave Hansen <haveblue@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
This commit is contained in:
Dave Hansen
2008-02-15 14:37:48 -08:00
committed by Al Viro
parent 42a74f206b
commit 4a3fd211cc
4 changed files with 127 additions and 14 deletions
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36
fs/open.c
View File

@ -730,6 +730,35 @@ out:
return error;
}
/*
* You have to be very careful that these write
* counts get cleaned up in error cases and
* upon __fput(). This should probably never
* be called outside of __dentry_open().
*/
static inline int __get_file_write_access(struct inode *inode,
struct vfsmount *mnt)
{
int error;
error = get_write_access(inode);
if (error)
return error;
/*
* Do not take mount writer counts on
* special files since no writes to
* the mount itself will occur.
*/
if (!special_file(inode->i_mode)) {
/*
* Balanced in __fput()
*/
error = mnt_want_write(mnt);
if (error)
put_write_access(inode);
}
return error;
}
static struct file *__dentry_open(struct dentry *dentry, struct vfsmount *mnt,
int flags, struct file *f,
int (*open)(struct inode *, struct file *))
@ -742,7 +771,7 @@ static struct file *__dentry_open(struct dentry *dentry, struct vfsmount *mnt,
FMODE_PREAD | FMODE_PWRITE;
inode = dentry->d_inode;
if (f->f_mode & FMODE_WRITE) {
error = get_write_access(inode);
error = __get_file_write_access(inode, mnt);
if (error)
goto cleanup_file;
}
@ -784,8 +813,11 @@ static struct file *__dentry_open(struct dentry *dentry, struct vfsmount *mnt,
cleanup_all:
fops_put(f->f_op);
if (f->f_mode & FMODE_WRITE)
if (f->f_mode & FMODE_WRITE) {
put_write_access(inode);
if (!special_file(inode->i_mode))
mnt_drop_write(mnt);
}
file_kill(f);
f->f_path.dentry = NULL;
f->f_path.mnt = NULL;