Commit 85c59580 authored Sep 20, 2007 by Pavel Emelyanov Committed by J. Bruce Fields Oct 09, 2007

locks: Fix potential OOPS in generic_setlease()



This code is run under lock_kernel(), which is dropped during
sleeping operations, so the following race is possible:

CPU1:                                CPU2:
  vfs_setlease();                    vfs_setlease();
  lock_kernel();
                                     lock_kernel(); /* spin */
  generic_setlease():
    ...
    for (before = ...)
    /* here we found some lease after
     * which we will insert the new one
     */
    fl = locks_alloc_lock();
    /* go to sleep in this allocation and
     * drop the BKL
     */
                                     generic_setlease():
                                       ...
                                       for (before = ...)
                                       /* here we find the "before" pointing
                                        * at the one we found on CPU1
                                        */
                                      ->fl_change(my_before, arg);
                                              lease_modify();
                                                     locks_free_lock();
                                                     /* and we freed it */
                                     ...
                                     unlock_kernel();
   locks_insert_lock(before, fl);
   /* OOPS! We have just tried to add the lease
    * at the tail of already removed one
    */

The similar races are already handled in other code - all the
allocations are performed before any checks/updates.

Thanks to Kamalesh Babulal for testing and for a bug report on an
earlier version.

Signed-off-by: Pavel Emelyanov <xemul@openvz.org>
Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu>
Cc: Kamalesh Babulal <kamalesh@linux.vnet.ibm.com>

parent f0c1cd0e

fs/locks.c

+12 −9

Original line number	Diff line number	Diff line
		@@ -1343,6 +1343,7 @@ int fcntl_getlease(struct file *filp)
		int generic_setlease(struct file filp, long arg, struct file_lock *flp)
		{
		struct file_lock fl, before, my_before = NULL, lease;
		struct file_lock *new_fl = NULL;
		struct dentry *dentry = filp->f_path.dentry;
		struct inode *inode = dentry->d_inode;
		int error, rdlease_count = 0, wrlease_count = 0;
		@@ -1369,6 +1370,11 @@ int generic_setlease(struct file filp, long arg, struct file_lock *flp)
		\|\| (atomic_read(&inode->i_count) > 1)))
		goto out;

		error = -ENOMEM;
		new_fl = locks_alloc_lock();
		if (new_fl == NULL)
		goto out;

		/*
		* At this point, we know that if there is an exclusive
		* lease on this file, then we hold it on this filp
		@@ -1411,18 +1417,15 @@ int generic_setlease(struct file filp, long arg, struct file_lock *flp)
		if (!leases_enable)
		goto out;

		error = -ENOMEM;
		fl = locks_alloc_lock();
		if (fl == NULL)
		goto out;

		locks_copy_lock(fl, lease);
		locks_copy_lock(new_fl, lease);
		locks_insert_lock(before, new_fl);

		locks_insert_lock(before, fl);
		*flp = new_fl;
		return 0;

		*flp = fl;
		error = 0;
		out:
		if (new_fl != NULL)
		locks_free_lock(new_fl);
		return error;
		}
		EXPORT_SYMBOL(generic_setlease);

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