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>, firstname.lastname@example.org Subject: Re: [PATCH] Revert "floppy: reintroduce O_NDELAY fix" Date: Wed, 18 Aug 2021 18:53:58 +0300 [thread overview] Message-ID: <email@example.com> (raw) In-Reply-To: <nycvar.YFH.firstname.lastname@example.org> Hi, 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 libblkid probing. Probably there is a better fix for , maybe even an additional workaround for floppies in libblkid. They already have workarounds for cdroms https://github.com/karelzak/util-linux/commit/dc30fd4383e57a0440cdb0e16ba5c4336a43b290 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... Regards, Denis
next prev parent reply other threads:[~2021-08-18 15:54 UTC|newest] Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top 2021-07-23 18:47 [BUG] FLOPPY DRIVER since 5.10.20 Mark Hounschell 2021-07-26 7:57 ` Denis Efremov 2021-07-26 11:15 ` Mark Hounschell 2021-07-26 11:17 ` Mark Hounschell 2021-07-26 11:37 ` Denis Efremov 2021-07-26 12:23 ` Mark Hounschell 2021-07-26 16:34 ` Denis Efremov 2021-07-30 5:15 ` Denis Efremov 2021-08-01 11:14 ` Kurt Garloff 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
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