On Fri, Jun 10, 2011 at 04:24:00PM -0400, Mimi Zohar wrote:
> 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.
Actually, offhand I can't see why that wouldn't be OK.
Though I think we still end up needing something like i_blockleases to
handle unlink, link, rename, chown, and chmod.
--b.
>
> 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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