linux-kernel - Re: [PATCH 0/3] PM, vfs: use filesystem freezing instead of kthread freezer

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <CAJZ5v0iamJrZ5FtX8PuiAhH9yLdGapmYq40HBHtQ7QGRUEPooA@mail.gmail.com>
Date:	Tue, 3 Nov 2015 22:33:21 +0100
From:	"Rafael J. Wysocki" <rafael@...nel.org>
To:	Jan Kara <jack@...e.cz>
Cc:	Dave Chinner <david@...morbit.com>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Jiri Kosina <jikos@...nel.org>,
	Alan Stern <stern@...land.harvard.edu>,
	Pavel Machek <pavel@....cz>,
	"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
	Christoph Hellwig <hch@....de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Al Viro <viro@...iv.linux.org.uk>, Tejun Heo <tj@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-fsdevel@...r.kernel.org,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>
Subject: Re: [PATCH 0/3] PM, vfs: use filesystem freezing instead of kthread freezer

Hi,

On Tue, Nov 3, 2015 at 10:31 AM, Jan Kara <jack@...e.cz> wrote:
> On Tue 03-11-15 11:10:53, Dave Chinner wrote:
>> On Mon, Nov 02, 2015 at 03:43:07AM +0100, Rafael J. Wysocki wrote:
>> > I guess it may also helps to address the case when a device is removed from a
>> > suspended system, written to on another system in the meantime and inserted
>> > back into the (still suspended) original system which then is resumed.  Today
>> > this is an almost guaranteed data corruption scenario, but if the filesystem in
>> > question is properly frozen during suspend, the driver should be able to detect
>> > superblock changes during unfreeze.
>>
>> Never going to work. There is no guarantee that a write to a
>> filesystem by a third party device is going to change the superblock
>> (or any metadata in the rest of the filesystem) in any detectable
>> way.  Hence freezing filesystems will not prevent Bad Things
>> Happening if you do this while your system is suspended.
>
> Agreed, we should never advertise something like this works. OTOH the truth
> is that e.g. in ext4 case a simple check in ext4_unfreeze() could catch 90%
> of cases where user shot himself in the foot like this (i.e., ext4 driver
> will update write time in superblock if it gets mounted somewhere else and
> we can check whether that didn't change in ext4_unfreeze()) and refuse to
> touch the filesystem... It is not 100% reliable since user could have used
> e.g. debuge2fs to arbitrarily modify the filesystem but in such cases they
> have to know what they are doing anyway.

Well, my idea was to use this for sanity checking.  I guess that
sanity checks here don't really hurt, do they?  And if they fail,
perhaps we can just avoid touching the fs again for safety reasons?

Thanks,
Rafael
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/