From: Denis Efremov <firstname.lastname@example.org>
To: Jiri Kosina <email@example.com>
Cc: firstname.lastname@example.org, email@example.com,
firstname.lastname@example.org, Mark Hounschell <email@example.com>,
Wim Osterholt <firstname.lastname@example.org>,
Kurt Garloff <email@example.com>,
Subject: Re: [PATCH] Revert "floppy: reintroduce O_NDELAY fix"
Date: Wed, 18 Aug 2021 18:53:58 +0300 [thread overview]
Message-ID: <firstname.lastname@example.org> (raw)
On 8/16/21 10:17 AM, Jiri Kosina wrote:
> On Sun, 8 Aug 2021, Denis Efremov wrote:
>> The patch breaks userspace implementations (e.g. fdutils) and introduces
>> regressions in behaviour. Previously, it was possible to O_NDELAY open a
>> floppy device with no media inserted or with write protected media without
>> an error. Some userspace tools use this particular behavior for probing.
>> It's not the first time when we revert this patch. Previous revert is in
>> commit f2791e7eadf4 (Revert "floppy: refactor open() flags handling").
>> This reverts commit 8a0c014cd20516ade9654fc13b51345ec58e7be8.
> By reverting it you bring back the bugs that were fixed by it
I agree with you, that O_NDELAY is broken for floppies (and always been).
However, just by removing O_NDELAY we break many existing tools that use
it for probing and ioctl-only opens. With the patch tools fail to open the
device without a diskette and try to read a diskette if there is one (this is
not as fast on a real hardware as in QEMU).
I think that there should be a better fix that doesn't break existing tools.
It appears that people still use software that depends on O_NDELAY in floppies.
Same patch was already reverted in 2016 (presumably) by the same reason.
> -- e.g. the
> possibility to livelock mmap() on the returned fd to keep waiting on the
> page unlock bit forever
As far as I understand this is a problem only for syzkaller.
And this is not a security issue nowadays since most distributions
(I don't know exceptions) require at least "disk" group to access floppies.
Do you know a link for the syzkaller reproducer?
> or the functionality bug reported at , and
> likely others.
>  https://bugzilla.suse.com/show_bug.cgi?id=1181018
The patch starts to return -ENXIO for O_NDELAY|O_RDONLY opens and devices
without a diskette. I don't think this is an expected behavior during
Probably there is a better fix for , maybe even an additional workaround
for floppies in libblkid. They already have workarounds for cdroms
I started to add simple tests https://lkml.org/lkml/2021/8/18/845
However, I failed to reproduce mount bug , probably
because I don't know how to configure cloudinit properly. I tried to reproduce
a mount fail bug with open("/dev/fd0", O_NDELAY|O_RDONLY) and mount("/dev/fd0", ...)
but it works. Looks like there should be something else in between...
next prev parent reply other threads:[~2021-08-18 15:54 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <email@example.com>
2021-08-08 7:42 ` [PATCH] Revert "floppy: reintroduce O_NDELAY fix" Denis Efremov
2021-08-16 7:17 ` Jiri Kosina
2021-08-18 15:53 ` Denis Efremov [this message]
2021-08-30 9:20 ` Thorsten Leemhuis
2021-09-20 11:29 ` Thorsten Leemhuis
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