On Thu, 2011-06-09 at 20:10 -0400, J. Bruce Fields wrote:
> From: J. Bruce Fields <bfields@xxxxxxxxxx>
>
> Since break_lease is called before i_writecount is incremented, there's
> a window between the two where a setlease call would have no way to know
> that an open is about to happen.
So unless the break_lease() call is moved from may_open() to after
nameidata_to_filp(), I don't see any other options.
Mimi
> We fix this by adding a new inode field, i_blockleases, that is
> incremented while a lease-breaking operation is in progress.
>
> We will later reuse i_blockleases to enforce lease-breaking for rename,
> unlink, etc.
>
> Signed-off-by: J. Bruce Fields <bfields@xxxxxxxxxx>
> ---
> fs/inode.c | 1 +
> fs/locks.c | 28 ++++++++++++++++++++++++++++
> fs/namei.c | 6 +++++-
> include/linux/fs.h | 3 +++
> 4 files changed, 37 insertions(+), 1 deletions(-)
>
> diff --git a/fs/inode.c b/fs/inode.c
> index 33c963d..4f253a2 100644
> --- a/fs/inode.c
> +++ b/fs/inode.c
> @@ -198,6 +198,7 @@ int inode_init_always(struct super_block *sb, struct inode *inode)
> inode->i_uid = 0;
> inode->i_gid = 0;
> atomic_set(&inode->i_writecount, 0);
> + atomic_set(&inode->i_blockleases, 0);
> inode->i_size = 0;
> inode->i_blocks = 0;
> inode->i_bytes = 0;
> diff --git a/fs/locks.c b/fs/locks.c
> index 0a4f50d..7699b1b 100644
> --- a/fs/locks.c
> +++ b/fs/locks.c
> @@ -1164,6 +1164,32 @@ static void time_out_leases(struct inode *inode)
> }
> }
>
> +/* Disallow all leases (read or write): */
> +void disallow_leases(struct inode *inode, int flags)
> +{
> + if (!inode)
> + return;
> + if (!S_ISREG(inode->i_mode))
> + return;
> + if ((flags & O_ACCMODE) == O_RDONLY)
> + return;
> + atomic_inc(&inode->i_blockleases);
> +}
> +EXPORT_SYMBOL_GPL(disallow_leases);
> +
> +void reallow_leases(struct inode *inode, int flags)
> +{
> + if (!inode)
> + return;
> + if (!S_ISREG(inode->i_mode))
> + return;
> + if ((flags & O_ACCMODE) == O_RDONLY)
> + return;
> + BUG_ON(atomic_read(&inode->i_blockleases) <= 0);
> + atomic_dec(&inode->i_blockleases);
> +}
> +EXPORT_SYMBOL_GPL(reallow_leases);
> +
> /**
> * __break_lease - revoke all outstanding leases on file
> * @inode: the inode of the file to return
> @@ -1369,6 +1395,8 @@ int generic_setlease(struct file *filp, long arg, struct file_lock **flp)
>
> if (arg != F_UNLCK) {
> error = -EAGAIN;
> + if (atomic_read(&inode->i_blockleases))
> + goto out;
> if ((arg == F_RDLCK) && (atomic_read(&inode->i_writecount) > 0))
> goto out;
> if ((arg == F_WRLCK)
> diff --git a/fs/namei.c b/fs/namei.c
> index 3cb616d..079e68c 100644
> --- a/fs/namei.c
> +++ b/fs/namei.c
> @@ -2277,10 +2277,14 @@ ok:
> want_write = 1;
> }
> common:
> + disallow_leases(nd->path.dentry->d_inode, open_flag);
> error = may_open(&nd->path, acc_mode, open_flag);
> - if (error)
> + if (error) {
> + reallow_leases(nd->path.dentry->d_inode, open_flag);
> goto exit;
> + }
> filp = nameidata_to_filp(nd);
> + reallow_leases(nd->path.dentry->d_inode, open_flag);
> if (!IS_ERR(filp)) {
> error = ima_file_check(filp, op->acc_mode);
> if (error) {
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index 1b95af3..daf8443 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -796,6 +796,7 @@ struct inode {
> #ifdef CONFIG_IMA
> atomic_t i_readcount; /* struct files open RO */
> #endif
> + atomic_t i_blockleases; /* setlease fails when >0 */
> atomic_t i_writecount;
> #ifdef CONFIG_SECURITY
> void *i_security;
> @@ -1161,6 +1162,8 @@ extern void lease_get_mtime(struct inode *, struct timespec *time);
> extern int generic_setlease(struct file *, long, struct file_lock **);
> extern int vfs_setlease(struct file *, long, struct file_lock **);
> extern int lease_modify(struct file_lock **, int);
> +extern void disallow_leases(struct inode *, int flags);
> +extern void reallow_leases(struct inode *, int flags);
> extern int lock_may_read(struct inode *, loff_t start, unsigned long count);
> extern int lock_may_write(struct inode *, loff_t start, unsigned long count);
> extern void lock_flocks(void);
--
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