From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from m12-14.163.com ([220.181.12.14]:56603 "EHLO m12-14.163.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726431AbeK0Uyj (ORCPT ); Tue, 27 Nov 2018 15:54:39 -0500 Date: Tue, 27 Nov 2018 17:57:12 +0800 From: PanBian To: Jan Kara Cc: Alexander Viro , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH V2] namei: free new_dentry late Message-ID: <20181127095712.GA32100@bp> Reply-To: PanBian References: <1543104923-81192-1-git-send-email-bianpan2016@163.com> <20181127092551.GC16301@quack2.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20181127092551.GC16301@quack2.suse.cz> Sender: linux-fsdevel-owner@vger.kernel.org List-ID: 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. Best regards, Pan > > Honza > > > --- > > V2: correct the fixes commit information > > --- > > fs/namei.c | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > 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