linux-kernel - Re: [PATCH v2 09/24] file: Replace fcheck_files with files_lookup_fd

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Message-ID: <20201207224903.GA4117703@ZenIV.linux.org.uk>
Date:   Mon, 7 Dec 2020 22:49:03 +0000
From:   Al Viro <viro@...iv.linux.org.uk>
To:     "Eric W. Biederman" <ebiederm@...ssion.com>
Cc:     linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        criu@...nvz.org, bpf@...r.kernel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Christian Brauner <christian.brauner@...ntu.com>,
        Oleg Nesterov <oleg@...hat.com>,
        Cyrill Gorcunov <gorcunov@...il.com>,
        Jann Horn <jann@...jh.net>, Kees Cook <keescook@...omium.org>,
        Daniel P . Berrangé <berrange@...hat.com>,
        Jeff Layton <jlayton@...hat.com>,
        Miklos Szeredi <miklos@...redi.hu>,
        Matthew Wilcox <willy@...radead.org>,
        "J. Bruce Fields" <bfields@...ldses.org>,
        Trond Myklebust <trond.myklebust@...merspace.com>,
        Chris Wright <chrisw@...hat.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        Andrii Nakryiko <andriin@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...omium.org>
Subject: Re: [PATCH v2 09/24] file: Replace fcheck_files with
 files_lookup_fd_rcu

On Mon, Dec 07, 2020 at 10:46:57PM +0000, Al Viro wrote:
> On Fri, Nov 20, 2020 at 05:14:26PM -0600, Eric W. Biederman wrote:
> 
> >  /*
> >   * Check whether the specified fd has an open file.
> >   */
> > -#define fcheck(fd)	fcheck_files(current->files, fd)
> > +#define fcheck(fd)	files_lookup_fd_rcu(current->files, fd)
> 
> Huh?
> fs/file.c:1113: file = fcheck(oldfd);
> 	dup3(), under ->file_lock, no rcu_read_lock() in sight
> 
> fs/locks.c:2548:                f = fcheck(fd);
> 	fcntl_setlk(), ditto
> 
> fs/locks.c:2679:                f = fcheck(fd);
> 	fcntl_setlk64(), ditto
> 
> fs/notify/dnotify/dnotify.c:330:        f = fcheck(fd);
> 	fcntl_dirnotify(); this one _is_ under rcu_read_lock().
> 
> 
> IOW, unless I've missed something earlier in the series, this is wrong.

I have missed something, all right.  Ignore that comment...