From: Al Viro <viro@zeniv.linux.org.uk>
To: Miklos Szeredi <mszeredi@redhat.com>
Cc: linux-fsdevel@vger.kernel.org, Jan Kara <jack@suse.cz>,
Amir Goldstein <amir73il@gmail.com>, Karel Zak <kzak@redhat.com>,
Lennart Poettering <lennart@poettering.net>,
Ian Kent <raven@themaw.net>,
Christian Brauner <brauner@kernel.org>
Subject: Re: [RFC PATCH] fanotify: notify on mount attach and detach
Date: Thu, 28 Nov 2024 19:57:38 +0000 [thread overview]
Message-ID: <20241128195738.GG3387508@ZenIV> (raw)
In-Reply-To: <20241128144002.42121-1-mszeredi@redhat.com>
On Thu, Nov 28, 2024 at 03:39:59PM +0100, Miklos Szeredi wrote:
> Prior to this patch mount namespace changes could be monitored by polling
> /proc/self/mountinfo, which did not convey any information about what
> changed.
>
> To monitor an entire mount namespace with this new interface, watches need
> to be added to all existing mounts. This can be done by performing
> listmount()/statmount() recursively at startup and when a new mount is
> added.
First impression is that it's bloody awful, TBH. You are calling fsnotify()
under mount_lock; in effect, *ANY* path_init() call done during that time
will be spinning in __read_seqcount_begin() until you are done with that
shite.
And it's _very_ easy to generate a lot of such events with a single syscall;
that doesn't even need sroot - a root in container will suffice.
So... why is it not a DoS?
next prev parent reply other threads:[~2024-11-28 19:57 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-11-28 14:39 [RFC PATCH] fanotify: notify on mount attach and detach Miklos Szeredi
2024-11-28 16:43 ` Amir Goldstein
2024-11-29 7:16 ` Miklos Szeredi
2024-11-29 10:23 ` Amir Goldstein
2024-12-03 15:36 ` Miklos Szeredi
2024-11-28 19:57 ` Al Viro [this message]
2024-11-29 7:10 ` Miklos Szeredi
2024-11-29 9:25 ` Christian Brauner
2024-12-03 11:40 ` Karel Zak
2024-12-03 13:03 ` Amir Goldstein
2024-12-03 16:42 ` Jan Kara
2024-12-04 11:30 ` Christian Brauner
2024-12-06 15:18 ` Miklos Szeredi
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