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leases: fix write-open/read-lease race

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In setlease, we use i_writecount to decide whether we can give out a
read lease.

In open, we break leases before incrementing i_writecount.

There is therefore a window between the break lease and the i_writecount
increment when setlease could add a new read lease.

This would leave us with a simultaneous write open and read lease, which
shouldn't happen.

Signed-off-by: J. Bruce Fields <bfields@redhat.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
This commit is contained in:
J. Bruce Fields 2011-09-21 10:58:13 -04:00 committed by root
parent 79835a710d
commit f3c7691e8d
2 changed files with 5 additions and 4 deletions
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5
fs/namei.c
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@ -2035,10 +2035,7 @@ static int may_open(struct path *path, int acc_mode, int flag)
if (flag & O_NOATIME && !inode_owner_or_capable(inode))
return -EPERM;
/*
* Ensure there are no outstanding leases on the file.
*/
return break_lease(inode, flag);
return 0;
}
static int handle_truncate(struct file *filp)

4
fs/open.c
View file

@ -685,6 +685,10 @@ static struct file *__dentry_open(struct dentry *dentry, struct vfsmount *mnt,
if (error)
goto cleanup_all;
error = break_lease(inode, f->f_flags);
if (error)
goto cleanup_all;
if (!open && f->f_op)
open = f->f_op->open;
if (open) {