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From: Miklos Szeredi <mszeredi@redhat.com>
To: Greg Kurz <groug@kaod.org>
Cc: Daniel Berrange <berrange@redhat.com>,
	QEMU Developers <qemu-devel@nongnu.org>,
	P J P <ppandit@redhat.com>, virtio-fs-list <virtio-fs@redhat.com>,
	Alex Xu <alex@alxu.ca>, Stefan Hajnoczi <stefanha@redhat.com>,
	Laszlo Ersek <lersek@redhat.com>, Vivek Goyal <vgoyal@redhat.com>
Subject: Re: [Virtio-fs] [PATCH v2] virtiofsd: prevent opening of special files (CVE-2020-35517)
Date: Wed, 27 Jan 2021 10:25:28 +0100	[thread overview]
Message-ID: <CAOssrKdh3kqKN4uGE=s5eiymd2MXKsRXUegqRH-TFhqYOK7WOA@mail.gmail.com> (raw)
In-Reply-To: <20210126181604.1a4c69c6@bahia.lan>

On Tue, Jan 26, 2021 at 6:18 PM Greg Kurz <groug@kaod.org> wrote:
>
> On Tue, 26 Jan 2021 10:35:02 +0000
> Stefan Hajnoczi <stefanha@redhat.com> wrote:

> The patch looks pretty good to me. It just seems to be missing a change in
> lo_create():
>
>     fd = openat(parent_inode->fd, name, (fi->flags | O_CREAT) & ~O_NOFOLLOW,
>                 mode);
>
> A malicious guest could have created anything called ${name} in this directory
> before calling FUSE_CREATE and we'll open it blindly, or I'm missing something ?

Right, this seems like an omission.

Also the "& ~O_NOFOLLOW" looks like a copy-paste bug, since unlike
lo_open(), lo_create() is not opening a proc symlink.

So that should be replaced with "| O_NOFOLLOW"

Thanks,
Miklos



WARNING: multiple messages have this Message-ID (diff)
From: Miklos Szeredi <mszeredi@redhat.com>
To: Greg Kurz <groug@kaod.org>
Cc: Daniel Berrange <berrange@redhat.com>,
	QEMU Developers <qemu-devel@nongnu.org>,
	P J P <ppandit@redhat.com>, virtio-fs-list <virtio-fs@redhat.com>,
	Alex Xu <alex@alxu.ca>, Laszlo Ersek <lersek@redhat.com>,
	Vivek Goyal <vgoyal@redhat.com>
Subject: Re: [Virtio-fs] [PATCH v2] virtiofsd: prevent opening of special files (CVE-2020-35517)
Date: Wed, 27 Jan 2021 10:25:28 +0100	[thread overview]
Message-ID: <CAOssrKdh3kqKN4uGE=s5eiymd2MXKsRXUegqRH-TFhqYOK7WOA@mail.gmail.com> (raw)
In-Reply-To: <20210126181604.1a4c69c6@bahia.lan>

On Tue, Jan 26, 2021 at 6:18 PM Greg Kurz <groug@kaod.org> wrote:
>
> On Tue, 26 Jan 2021 10:35:02 +0000
> Stefan Hajnoczi <stefanha@redhat.com> wrote:

> The patch looks pretty good to me. It just seems to be missing a change in
> lo_create():
>
>     fd = openat(parent_inode->fd, name, (fi->flags | O_CREAT) & ~O_NOFOLLOW,
>                 mode);
>
> A malicious guest could have created anything called ${name} in this directory
> before calling FUSE_CREATE and we'll open it blindly, or I'm missing something ?

Right, this seems like an omission.

Also the "& ~O_NOFOLLOW" looks like a copy-paste bug, since unlike
lo_open(), lo_create() is not opening a proc symlink.

So that should be replaced with "| O_NOFOLLOW"

Thanks,
Miklos


  reply	other threads:[~2021-01-27  9:26 UTC|newest]

Thread overview: 33+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-01-26 10:35 [PATCH v2] virtiofsd: prevent opening of special files (CVE-2020-35517) Stefan Hajnoczi
2021-01-26 10:35 ` [Virtio-fs] " Stefan Hajnoczi
2021-01-26 10:36 ` Daniel P. Berrangé
2021-01-26 10:36   ` [Virtio-fs] " Daniel P. Berrangé
2021-01-26 10:47 ` Liam Merwick
2021-01-26 17:16 ` Greg Kurz
2021-01-27  9:25   ` Miklos Szeredi [this message]
2021-01-27  9:25     ` Miklos Szeredi
2021-01-27 10:20     ` Greg Kurz
2021-01-27 10:20       ` Greg Kurz
2021-01-27 10:34       ` Miklos Szeredi
2021-01-27 10:34         ` Miklos Szeredi
2021-01-27 13:49         ` Greg Kurz
2021-01-27 13:49           ` Greg Kurz
2021-01-27 14:09           ` Miklos Szeredi
2021-01-27 14:09             ` Miklos Szeredi
2021-01-27 15:09             ` Greg Kurz
2021-01-27 15:09               ` Greg Kurz
2021-01-27 15:22               ` Miklos Szeredi
2021-01-27 15:22                 ` Miklos Szeredi
2021-01-27 15:35                 ` Greg Kurz
2021-01-27 15:35                   ` Greg Kurz
2021-01-27 15:47                   ` Miklos Szeredi
2021-01-27 15:47                     ` Miklos Szeredi
2021-01-27 15:52                     ` Miklos Szeredi
2021-01-27 15:52                       ` Miklos Szeredi
2021-01-28 12:14                       ` Greg Kurz
2021-01-28 12:14                         ` Greg Kurz
2021-01-28 14:00                         ` Miklos Szeredi
2021-01-28 14:00                           ` Miklos Szeredi
2021-01-28 14:26                           ` Greg Kurz
2021-01-28 14:26                             ` Greg Kurz
2021-01-27 10:18   ` Stefan Hajnoczi

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