From: JeffleXu <jefflexu@linux.alibaba.com>
To: Greg Kurz <groug@kaod.org>
Cc: "Dr. David Alan Gilbert" <dgilbert@redhat.com>,
miklos@szeredi.hu, virtualization@lists.linux-foundation.org,
virtio-fs@redhat.com, joseph.qi@linux.alibaba.com,
stefanha@redhat.com, linux-fsdevel@vger.kernel.org,
vgoyal@redhat.com
Subject: Re: [Virtio-fs] [virtiofsd PATCH v4 4/4] virtiofsd: support per-file DAX in FUSE_LOOKUP
Date: Wed, 8 Sep 2021 18:34:53 +0800 [thread overview]
Message-ID: <88041d90-d170-3ae1-903e-2fa32e51027f@linux.alibaba.com> (raw)
In-Reply-To: <20210824121515.5419d6a7@bahia.lan>
On 8/24/21 6:15 PM, Greg Kurz wrote:
> On Fri, 20 Aug 2021 13:03:23 +0800
> JeffleXu <jefflexu@linux.alibaba.com> wrote:
>>
>> Fine. Got it. However the returned fd (opened without O_PATH) is only
>> used for FS_IOC_GETFLAGS/FS_IOC_FSGETXATTR ioctl, while in most cases
>> for special device files, these two ioctls should return -ENOTTY.
>>
>
> The actual problem is that a FIFO will cause openat() to block until
> the other end of the FIFO is open for writing...
Got it.
>
>> If it's really a security issue, then lo_inode_open() could be used to
>
> ... and cause a DoS on virtiofsd. So yes, this is a security issue and
> lo_inode_open() was introduced specifically to handle this.
>
>> get a temporary fd, i.e., check if it's a special file before opening.
>> After all, FUSE_OPEN also handles in this way. Besides, I can't
>> understand what "race-free way" means.
>>
>
> "race-free way" means a way that guarantees that file type
> cannot change between the time you check it and the time
> you open it (TOCTOU error). For example, doing a plain stat(),
> checking st_mode and proceeding to open() is wrong : nothing
> prevents the file to be unlinked and replaced by something
> else between stat() and open().
>
> We avoid that by keeping O_PATH fds around and using
> lo_inode_open() instead of openat().
Thanks for the detailed explanation. Got it.
>
> In your case, it seems that you should do the checking after
> you have an actual lo_inode for the target file, and pass
> that to lo_should_enable_dax() instead of the parent lo_inode
> and target name.
>
Yes, that will be more reasonable. Thanks.
--
Thanks,
Jeffle
next prev parent reply other threads:[~2021-09-08 10:34 UTC|newest]
Thread overview: 52+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-08-17 2:22 [PATCH v4 0/8] fuse,virtiofs: support per-file DAX Jeffle Xu
2021-08-17 2:22 ` [PATCH v4 1/8] fuse: add fuse_should_enable_dax() helper Jeffle Xu
2021-08-17 2:22 ` [PATCH v4 2/8] fuse: Make DAX mount option a tri-state Jeffle Xu
2021-08-17 2:22 ` [PATCH v4 3/8] fuse: support per-file DAX Jeffle Xu
2021-08-17 2:22 ` [PATCH v4 4/8] fuse: negotiate if server/client supports " Jeffle Xu
2021-08-17 2:22 ` [PATCH v4 5/8] fuse: enable " Jeffle Xu
2021-08-17 2:22 ` [PATCH v4 6/8] fuse: mark inode DONT_CACHE when per-file DAX indication changes Jeffle Xu
2021-08-17 10:26 ` [Virtio-fs] " Dr. David Alan Gilbert
2021-08-17 13:23 ` JeffleXu
2021-08-17 2:22 ` [PATCH v4 7/8] fuse: support changing per-file DAX flag inside guest Jeffle Xu
2021-08-17 2:22 ` [PATCH v4 8/8] fuse: show '-o dax=inode' option only when FUSE server supports Jeffle Xu
2021-08-17 2:23 ` [virtiofsd PATCH v4 0/4] virtiofsd: support per-file DAX Jeffle Xu
2021-08-17 2:23 ` [virtiofsd PATCH v4 1/4] virtiofsd: add .ioctl() support Jeffle Xu
2021-08-18 17:33 ` Vivek Goyal
2021-08-17 2:23 ` [virtiofsd PATCH v4 2/4] virtiofsd: expand fuse protocol to support per-file DAX Jeffle Xu
2021-08-17 2:23 ` [virtiofsd PATCH v4 3/4] virtiofsd: support per-file DAX negotiation in FUSE_INIT Jeffle Xu
2021-08-17 17:15 ` [Virtio-fs] " Dr. David Alan Gilbert
2021-08-18 5:28 ` JeffleXu
2021-08-19 13:57 ` Dr. David Alan Gilbert
2021-08-18 17:30 ` Vivek Goyal
2021-08-17 2:23 ` [virtiofsd PATCH v4 4/4] virtiofsd: support per-file DAX in FUSE_LOOKUP Jeffle Xu
2021-08-17 19:00 ` [Virtio-fs] " Dr. David Alan Gilbert
2021-08-18 5:46 ` JeffleXu
2021-08-19 13:08 ` Dr. David Alan Gilbert
2021-08-20 5:03 ` JeffleXu
2021-08-24 10:15 ` Greg Kurz
2021-09-08 10:34 ` JeffleXu [this message]
2021-08-17 8:06 ` [PATCH v4 0/8] fuse,virtiofs: support per-file DAX Miklos Szeredi
2021-08-17 9:32 ` [Virtio-fs] " Dr. David Alan Gilbert
2021-08-17 10:09 ` Miklos Szeredi
2021-08-17 10:37 ` Dr. David Alan Gilbert
2021-08-17 13:08 ` JeffleXu
2021-08-17 14:11 ` Miklos Szeredi
2021-08-17 15:19 ` Vivek Goyal
2021-08-17 14:54 ` Vivek Goyal
2021-08-18 5:10 ` JeffleXu
2021-08-19 6:14 ` JeffleXu
2021-08-17 12:40 ` Vivek Goyal
2021-09-16 8:21 ` JeffleXu
2021-09-18 3:06 ` JeffleXu
2021-09-19 19:45 ` Vivek Goyal
2021-09-22 8:16 ` JeffleXu
2021-08-17 12:39 ` Vivek Goyal
2021-08-17 13:22 ` JeffleXu
2021-08-17 14:08 ` Miklos Szeredi
2021-08-18 3:39 ` JeffleXu
2021-08-18 5:08 ` Miklos Szeredi
2021-08-18 16:58 ` Vivek Goyal
2021-09-03 5:30 ` JeffleXu
2021-09-07 14:51 ` Miklos Szeredi
2021-08-17 14:57 ` Vivek Goyal
2021-08-18 5:20 ` JeffleXu
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