From: Johannes Berg <johannes@sipsolutions.net>
To: Takashi Iwai <tiwai@suse.de>,
Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Cc: linux-wireless@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: systemd-rfkill regression on 5.11 and later kernels
Date: Thu, 18 Mar 2021 10:36:19 +0100 [thread overview]
Message-ID: <54859a03b8789a2800596067e06c8adb49a107f5.camel@sipsolutions.net> (raw)
In-Reply-To: <s5ha6r0kgt5.wl-tiwai@suse.de> (sfid-20210318_092815_512625_74D8A8A5)
Hi Takashi,
Oh yay :-(
> we've received a bug report about rfkill change that was introduced in
> 5.11. While the systemd-rfkill expects the same size of both read and
> write, the kernel rfkill write cuts off to the old 8 bytes while read
> gives 9 bytes, hence it leads the error:
> https://github.com/systemd/systemd/issues/18677
> https://bugzilla.opensuse.org/show_bug.cgi?id=1183147
> As far as I understand from the log in the commit 14486c82612a, this
> sounds like the intended behavior.
Not really? I don't even understand why we get this behaviour.
The code is this:
rfkill_fop_write():
...
/* we don't need the 'hard' variable but accept it */
if (count < RFKILL_EVENT_SIZE_V1 - 1)
return -EINVAL;
# this is actually 7 - RFKILL_EVENT_SIZE_V1 is 8
# (and obviously we get past this if and don't get -EINVAL
/*
* Copy as much data as we can accept into our 'ev' buffer,
* but tell userspace how much we've copied so it can determine
* our API version even in a write() call, if it cares.
*/
count = min(count, sizeof(ev));
# sizeof(ev) should be 9 since 'ev' is the new struct
if (copy_from_user(&ev, buf, count))
return -EFAULT;
...
ret = 0;
...
return ret ?: count;
Ah, no, I see. The bug says:
EDIT: above is with kernel-core-5.10.16-200.fc33.x86_64.
So you've recompiled systemd with 5.11 headers, but are running against
5.10 now, where the short write really was intentional - it lets you
detect that the new fields weren't handled by the kernel. If
The other issue is basically this (pre-fix) systemd code:
l = read(c.rfkill_fd, &event, sizeof(event));
...
if (l != RFKILL_EVENT_SIZE_V1) /* log/return error */
So ... honestly, I don't have all that much sympathy, when the uapi
header explicitly says we want to be able to change the size. But I
guess "no regressions" rules are hard, so ... dunno. I guess we can add
a version/size ioctl and keep using 8 bytes unless you send that?
johannes
next prev parent reply other threads:[~2021-03-18 9:37 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-18 8:27 systemd-rfkill regression on 5.11 and later kernels Takashi Iwai
2021-03-18 9:26 ` Emmanuel Grumbach
2021-03-18 9:36 ` Johannes Berg [this message]
2021-03-18 10:07 ` Takashi Iwai
2021-03-18 10:50 ` Johannes Berg
2021-03-18 11:11 ` Takashi Iwai
2021-03-18 11:16 ` Johannes Berg
2021-03-19 22:15 ` Johannes Berg
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