[PATCH v2 03/17] locks: close potential race in lease_get_mtime

Jeff Layton
2014-09-04T12:39:17Z

lease_get_mtime is called without the i_lock held, so there's no
guarantee about the stability of the list. Between the time when we
assign "flock" and then dereference it to check whether it's a lease
and for write, the lease could be freed.

Ensure that that doesn't occur by taking the i_lock before trying
to check the lease.

Cc: J. Bruce Fields <bfields@fieldses.org>
Signed-off-by: Jeff Layton <jlayton@primarydata.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
---
fs/locks.c | 14 ++++++++++++--
1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/fs/locks.c b/fs/locks.c
index 18e87f11a25f..4031324e6cca 100644
--- a/fs/locks.c
+++ b/fs/locks.c
@@ -1456,8 +1456,18 @@ EXPORT_SYMBOL(__break_lease);
*/
void lease_get_mtime(struct inode *inode, struct timespec *time)
{
- struct file_lock *flock = inode->i_flock;
- if (flock && IS_LEASE(flock) && (flock->fl_type == F_WRLCK))
+ bool has_lease = false;
+ struct file_lock *flock;
+
+ if (inode->i_flock) {
+ spin_lock(&inode->i_lock);
+ flock = inode->i_flock;
+ if (flock && IS_LEASE(flock) && (flock->fl_type == F_WRLCK))
+ has_lease = true;
+ spin_unlock(&inode->i_lock);
+ }
+
+ if (has_lease)
*time = current_fs_time(inode->i_sb);
else
*time = inode->i_mtime;
--
1.9.3