linux-kernel - Re: [patch] floppy: suspend/resume fix

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-next>] [day] [month] [year] [list]

Date:	Sun, 12 Nov 2006 21:47:08 +0100 (MET)
From:	Mikael Pettersson <mikpe@...uu.se>
To:	mingo@...e.hu, rmk+lkml@....linux.org.uk
Cc:	akpm@...l.org, linux-kernel@...r.kernel.org
Subject: Re: [patch] floppy: suspend/resume fix

On Sun, 12 Nov 2006 19:40:01 +0000, Russell King wrote:
> On Sun, Nov 12, 2006 at 07:09:53PM +0100, Ingo Molnar wrote:
> > 
> > * Mikael Pettersson <mikpe@...uu.se> wrote:
> > 
> > > Sorry, no joy. The first access post-resume still fails and generates:
> > 
> > ok, then someone who knows the floppy driver better than me should put 
> > the right stuff into the suspend/resume hooks :-)
> 
> At a guess, what's probably happening is that the floppy drive, when
> powered on after resume, reports "disk changed" because it doesn't
> know any better.
> 
> We interpret "disk changed" to mean the disk has been removed and
> possibly changed (which _is_ correct) and thereby abort any further
> IO (irrespective of resume.)
> 
> Now, consider the following two scenarios:
> 
> 1. You suspend and then resume, leaving the disk in the floppy drive.
> 
> 2. You suspend, remove the floppy disk, insert a totally different disk
>    in the same drive, and then resume.
> 
> What should you do?  (Hint: without reading the disk and comparing it
> with what you have cached you don't know if the disk has been changed
> or not.)
> 
> If you argue that in case (1) you should continue to allow IO, then
> you potentially end up scribbling over a disk when someone does (2).
> 
> So I'd argue that the behaviour being seen by Mikael is the _safest_
> behaviour, and the most correct behaviour given the limitations of
> the hardware.

Note that my usage scenario consists of separate I/O commands:

1. boot
2. tar cf /dev/fd0 somefile
3. tar tvf /dev/fd0
4. suspend (close lid) and later resume (open lid) 
5. tar tvf /dev/fd0 (this one fails since 2.6.18-rc1)

Ages and ages ago the floppy driver would cache data so that
after e.g. one "tar tvf /dev/fd0" command, a new "tar tvf /dev/fd0"
wouldn't actually do any I/O. But nowadays, at least in all 2.6
kernels, that's not done and both "tar tvf /dev/fd0" commands
will read the media.

Thus I don't see any excuse for the kernel failing step 5 above.

/Mikael
-
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/