diff options
author | Pavel Emelyanov <xemul@openvz.org> | 2007-09-20 12:45:02 +0400 |
---|---|---|
committer | J. Bruce Fields <bfields@citi.umich.edu> | 2007-10-09 18:32:45 -0400 |
commit | 85c59580b30c82aa771aa33b37217a6b6851bc14 (patch) | |
tree | 02e96b437a63908ad3791021d352ad2aefff9936 /fs/locks.c | |
parent | f0c1cd0eaf0b127356c2c09e40305453bc361b0f (diff) | |
download | lwn-85c59580b30c82aa771aa33b37217a6b6851bc14.tar.gz lwn-85c59580b30c82aa771aa33b37217a6b6851bc14.zip |
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>
Diffstat (limited to 'fs/locks.c')
-rw-r--r-- | fs/locks.c | 21 |
1 files changed, 12 insertions, 9 deletions
diff --git a/fs/locks.c b/fs/locks.c index 282b6c11670a..43dbc7f566fa 100644 --- a/fs/locks.c +++ b/fs/locks.c @@ -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); |