linux-kernel - Re: [GIT PULL] proc fixes v2 for v5.8-rc1

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Message-ID: <CAHk-=wh7nZNf81QPcgpDh-0jzt2sOF3rdUEB0UcZvYFHDiMNkw@mail.gmail.com>
Date:   Fri, 12 Jun 2020 12:46:25 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     "Eric W. Biederman" <ebiederm@...ssion.com>,
        Alexey Dobriyan <adobriyan@...il.com>,
        Al Viro <viro@...iv.linux.org.uk>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Alexey Gladkov <gladkov.alexey@...il.com>
Subject: Re: [GIT PULL] proc fixes v2 for v5.8-rc1

On Fri, Jun 12, 2020 at 12:34 PM Eric W. Biederman
<ebiederm@...ssion.com> wrote:
>
> ebiederm@...ssion.com (Eric W. Biederman) writes:

What happened to that first version of the email? I never got it..

> Looking at the code the fsnotify watch should have been removed by
> fsnotify_sb_delete in generic_shutdown_super.

Hmm. Correct. The new_inode_pseudo() is for things that don't have
quotas, fsnotify or writeback.

That was used somewhat intentionally on /proc, though. /proc certainly
doesn't have quotas or writeback.

And fsnotify on /proc seems a bit questionably too. Do people actually
_do_ this and depend on it, or is this just about syzbot doing
something odd and thus showing the problem?

Anyway, I have pulled your fix, because I think it's reasonable and
safe, but I do wonder if we should have kept the new_inode_pseudo(),
and instead just make fsnotify say "you can't notify on an inode that
isn't on the superblock list". Hmm?

Is fsnotify on /proc really sensible? Do we actually generate any
useful notifications?

              Linus