Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752195Ab3GHNhv (ORCPT ); Mon, 8 Jul 2013 09:37:51 -0400 Received: from mail-yh0-f51.google.com ([209.85.213.51]:46364 "EHLO mail-yh0-f51.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751950Ab3GHNht (ORCPT ); Mon, 8 Jul 2013 09:37:49 -0400 From: Jeff Layton To: Al Viro Cc: Bruce Fields , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, Matthew Wilcox Subject: [PATCH] locks: close potential race between setlease and open Date: Mon, 8 Jul 2013 09:30:55 -0400 Message-Id: <1373290255-16977-1-git-send-email-jlayton@redhat.com> X-Mailer: git-send-email 1.8.1.4 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2808 Lines: 85 As Al Viro points out, there is an unlikely, but possible race between opening a file and setting a lease on it. generic_add_lease is done with the i_lock held, but the inode->i_flock check in break_lease is lockless. It's possible for another task doing an open to do the entire pathwalk and call break_lease between the point where generic_add_lease checks for a conflicting open and adds the lease to the list. If this occurs, we can end up with a lease set on the file with a conflicting open. To guard against that, check again for a conflicting open after adding the lease to the i_flock list. If the above race occurs, then we can simply unwind the lease setting and return -EAGAIN. Cc: Bruce Fields Reported-by: Al Viro Signed-off-by: Jeff Layton --- fs/locks.c | 31 ++++++++++++++++++++++++------- 1 file changed, 24 insertions(+), 7 deletions(-) diff --git a/fs/locks.c b/fs/locks.c index b27a300..9f7f647 100644 --- a/fs/locks.c +++ b/fs/locks.c @@ -1455,6 +1455,19 @@ int fcntl_getlease(struct file *filp) return type; } +static int +check_conflicting_open(struct dentry *dentry, long arg) +{ + struct inode *inode = dentry->d_inode; + + if ((arg == F_RDLCK) && (atomic_read(&inode->i_writecount) > 0)) + return -EAGAIN; + if ((arg == F_WRLCK) && ((d_count(dentry) > 1) || + (atomic_read(&inode->i_count) > 1))) + return -EAGAIN; + return 0; +} + static int generic_add_lease(struct file *filp, long arg, struct file_lock **flp) { struct file_lock *fl, **before, **my_before = NULL, *lease; @@ -1464,12 +1477,8 @@ static int generic_add_lease(struct file *filp, long arg, struct file_lock **flp lease = *flp; - error = -EAGAIN; - if ((arg == F_RDLCK) && (atomic_read(&inode->i_writecount) > 0)) - goto out; - if ((arg == F_WRLCK) - && ((d_count(dentry) > 1) - || (atomic_read(&inode->i_count) > 1))) + error = check_conflicting_open(dentry, arg); + if (error) goto out; /* @@ -1514,8 +1523,16 @@ static int generic_add_lease(struct file *filp, long arg, struct file_lock **flp goto out; locks_insert_lock(before, lease); - return 0; + /* + * The check in break_lease() is lockless. It's possible for another + * open to race in after we did the earlier check for a conflicting + * open but before the lease was inserted. Check again for a + * conflicting open and cancel the lease if there is one. + */ + error = check_conflicting_open(dentry, arg); + if (error) + locks_delete_lock(flp); out: return error; } -- 1.8.1.4 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/