From: Karel Zak <kzak@redhat.com>
To: Johannes Thumshirn <Johannes.Thumshirn@wdc.com>
Cc: Chris Hofstaedtler <chris@hofstaedtler.name>,
"util-linux@vger.kernel.org" <util-linux@vger.kernel.org>,
Coly Li <colyli@suse.de>, Damien Le Moal <Damien.LeMoal@wdc.com>
Subject: Re: [PATCH] blkzone: deny destructive ioctls on busy blockdev
Date: Fri, 15 May 2020 12:37:36 +0200 [thread overview]
Message-ID: <20200515103736.5jsezljksq64kofg@ws.net.home> (raw)
In-Reply-To: <SN4PR0401MB35982647432681A63CBABCA99BBD0@SN4PR0401MB3598.namprd04.prod.outlook.com>
On Fri, May 15, 2020 at 09:53:46AM +0000, Johannes Thumshirn wrote:
> On 15/05/2020 10:50, Chris Hofstaedtler wrote:
> > * Johannes Thumshirn <johannes.thumshirn@wdc.com> [200515 10:41]:
> >> If a user submits a zone management ioctl from user-space, like a zone
> >> reset and a file-system (like zonefs or f2fs) is mounted on the zoned
> >> block device, the zone will get reset and the file-system's cached value
> >> of the zone's write-pointer becomes invalid.
> >>
> >> Subsequent writes to this zone from the file-system will result in
> >> unaligned writes and the drive will error out.
> >
> > "error out" meaning what exactly?
>
> The drive will report an Unaligned Write error.
>
> >
> >> Open the block device file in exclusive mode for submitting these ioctls.
> >> If a file-system is mounted the kernel will return -EBUSY and we can't
> >> continue issuing the ioctl.
> >
> > Isn't this something the kernel should enforce, then?
>
> I did a patch for the kernel yesterday [1] enforcing this limitation, but as
> Damien said it's SYS_CAP_ADMIN and with great power comes great responsibility.
> We're also allowing other raw block device accesses on block devices.
>
> [1] https://lore.kernel.org/linux-block/BY5PR04MB69006DE86D1050620B5EDAA4E7BD0@BY5PR04MB6900.namprd04.prod.outlook.com/
>
> > What's to stop anybody from calling the ioctl from another tool,
> > without using O_EXCL?
>
> Nothing, but still we don't need to make one's life hard by letting blkzone go
> havoc with FS internal caching. If another tool does zone resets, it's up to them
> to check for mounted block devices.
O_EXCL good idea, it nothing unusual that you can do crazy things with
devices with mounted filesystem (see for example fdisk(s), wipefs, ...).
And sometimes it is valid use-case to do "bad" things and in this case
we have --force option in our tools (for example to avoid O_EXCL).
Karel
--
Karel Zak <kzak@redhat.com>
http://karelzak.blogspot.com
next prev parent reply other threads:[~2020-05-15 10:37 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-15 8:41 [PATCH] blkzone: deny destructive ioctls on busy blockdev Johannes Thumshirn
2020-05-15 8:50 ` Chris Hofstaedtler
2020-05-15 9:53 ` Johannes Thumshirn
2020-05-15 10:37 ` Karel Zak [this message]
2020-05-15 12:58 ` Karel Zak
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