From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx2.suse.de ([195.135.220.15]:53334 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726404AbeK0VDA (ORCPT ); Tue, 27 Nov 2018 16:03:00 -0500 Date: Tue, 27 Nov 2018 11:05:36 +0100 From: Jan Kara To: PanBian Cc: Jan Kara , Alexander Viro , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, Miklos Szeredi Subject: Re: [PATCH V2] namei: free new_dentry late Message-ID: <20181127100536.GF16301@quack2.suse.cz> References: <1543104923-81192-1-git-send-email-bianpan2016@163.com> <20181127092551.GC16301@quack2.suse.cz> <20181127095712.GA32100@bp> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20181127095712.GA32100@bp> Sender: linux-fsdevel-owner@vger.kernel.org List-ID: On Tue 27-11-18 17:57:12, PanBian wrote: > On Tue, Nov 27, 2018 at 10:25:51AM +0100, Jan Kara wrote: > > On Sun 25-11-18 08:15:23, Pan Bian wrote: > > > After calling dput(new_dentry), new_dentry is passed to fsnotify_move. > > > This may result in a use-after-free bug. This patch moves the put > > > operation late. > > > > > > Fixes: da1ce0670c14("vfs: add cross-rename") > > > Signed-off-by: Pan Bian > > > > The code is actually fine AFAICT. One new_dentry reference is passed into > > vfs_rename() and another one is acquired directly inside vfs_rename(). That > > is the one dropped early but there's still the original reference passed in > > protecting new_dentry from freeing. Am I missing something? > > I am not quite sure about the actual execution logic. But I guess new_dentry > reference may be dropped outside vfs_rename in cocurrent executions. > Otherwise, there is no need to acquire & drop new_dentry reference as it > is always alive along vfs_rename. I don't think that's the case. The dget() - dput() pair just looks superfluous to me in vfs_rename(). Am I missing something Miklos? Honza > > > diff --git a/fs/namei.c b/fs/namei.c > > > index 0cab649..8b104d9 100644 > > > --- a/fs/namei.c > > > +++ b/fs/namei.c > > > @@ -4498,7 +4498,6 @@ int vfs_rename(struct inode *old_dir, struct dentry *old_dentry, > > > unlock_two_nondirectories(source, target); > > > else if (target) > > > inode_unlock(target); > > > - dput(new_dentry); > > > if (!error) { > > > fsnotify_move(old_dir, new_dir, old_name.name, is_dir, > > > !(flags & RENAME_EXCHANGE) ? target : NULL, old_dentry); > > > @@ -4507,6 +4506,7 @@ int vfs_rename(struct inode *old_dir, struct dentry *old_dentry, > > > new_is_dir, NULL, new_dentry); > > > } > > > } > > > + dput(new_dentry); > > > release_dentry_name_snapshot(&old_name); > > > > > > return error; > > > -- > > > 2.7.4 > > > > > > > > -- > > Jan Kara > > SUSE Labs, CR > -- Jan Kara SUSE Labs, CR