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From: Linus Torvalds <torvalds@linux-foundation.org>
To: David Howells <dhowells@redhat.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>,
	Casey Schaufler <casey@schaufler-ca.com>,
	Stephen Smalley <sds@tycho.nsa.gov>,
	Nicolas Dichtel <nicolas.dichtel@6wind.com>,
	Ian Kent <raven@themaw.net>,
	Christian Brauner <christian@brauner.io>,
	Jeff Layton <jlayton@redhat.com>, Karel Zak <kzak@redhat.com>,
	Miklos Szeredi <mszeredi@redhat.com>,
	Linux API <linux-api@vger.kernel.org>,
	linux-fsdevel <linux-fsdevel@vger.kernel.org>,
	LSM List <linux-security-module@vger.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 3/4] watch_queue: Implement mount topology and attribute change notifications
Date: Fri, 24 Jul 2020 12:14:18 -0700	[thread overview]
Message-ID: <CAHk-=wjnQArU_BewVKQgYHy2mQD6LNKC5kkKXOm7GpNkJCapQg@mail.gmail.com> (raw)
In-Reply-To: <159559630912.2141315.16186899692832741137.stgit@warthog.procyon.org.uk>

This just can't be right.

On Fri, Jul 24, 2020 at 6:12 AM David Howells <dhowells@redhat.com> wrote:
>
> +
> +/**
> + * sys_watch_mount - Watch for mount topology/attribute changes
> + * @dfd: Base directory to pathwalk from or fd referring to mount.
> + * @filename: Path to mount to place the watch upon
> + * @at_flags: Pathwalk control flags
> + * @watch_fd: The watch queue to send notifications to.
> + * @watch_id: The watch ID to be placed in the notification (-1 to remove watch)
> + */
> +SYSCALL_DEFINE5(watch_mount, [...]
> +               int, watch_id)
...
> +       if (watch_id < -1 || watch_id > 0xff)
> +               return -EINVAL;
...
> +       ret = inode_permission(path.dentry->d_inode, MAY_EXEC);
> +       if (ret)
> +               goto err_path;
...
> +       if (watch_id >= 0) {
...
> +               watch = kzalloc(sizeof(*watch), GFP_KERNEL);
> +               if (!watch)
> +                       goto err_wlist;

So now you can basically allocate as much kernel memory as you want as
a regular user, as long as you have a mounted directory you can walk
(ie everybody).

Is there any limiting of watches anywhere? I don't see it.

I notice we already have this pattern elsewhere. I think we need to
fix this before we add more watch types.

Watch allocation shouldn't just be a kzalloc(). I think you should
have a "watch_allocate()" that does the initialization of id etc, but
also does some basic per-user watch resource tracking or something.

              Linus

  reply	other threads:[~2020-07-24 19:14 UTC|newest]

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-07-24 13:11 [PATCH 0/4] Mount notifications David Howells
2020-07-24 13:11 ` [PATCH 1/4] watch_queue: Make watch_sizeof() check record size David Howells
2020-07-24 13:11 ` [PATCH 2/4] watch_queue: Add security hooks to rule on setting mount watches David Howells
2020-07-24 13:11 ` [PATCH 3/4] watch_queue: Implement mount topology and attribute change notifications David Howells
2020-07-24 19:14   ` Linus Torvalds [this message]
2020-07-24 19:59   ` David Howells
2020-07-24 20:25     ` Linus Torvalds
2020-07-24 20:45     ` David Howells
2020-07-24 13:11 ` [PATCH 4/4] watch_queue: sample: Display mount tree " David Howells

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