From: PanBian <bianpan2016@163.com>
To: Jan Kara <jack@suse.cz>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>,
linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH V2] namei: free new_dentry late
Date: Tue, 27 Nov 2018 17:57:12 +0800 [thread overview]
Message-ID: <20181127095712.GA32100@bp> (raw)
In-Reply-To: <20181127092551.GC16301@quack2.suse.cz>
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 <bianpan2016@163.com>
>
> 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 <jack@suse.com>
> SUSE Labs, CR
next prev parent reply other threads:[~2018-11-27 9:57 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-11-25 0:15 [PATCH V2] namei: free new_dentry late Pan Bian
2018-11-27 9:25 ` Jan Kara
2018-11-27 9:57 ` PanBian [this message]
2018-11-27 10:05 ` Jan Kara
2018-11-27 10:33 ` Miklos Szeredi
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