linux-kernel - Re: [PATCH 4.9 183/271] signal: Allow cifs and drbd to receive their terminating signals

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Date:   Wed, 29 Jan 2020 14:12:03 -0500
From:   Sasha Levin <sashal@...nel.org>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Thomas Voegtle <tv@...96.de>, linux-kernel@...r.kernel.org,
        stable@...r.kernel.org, ronnie sahlberg <ronniesahlberg@...il.com>,
        Christoph Böhmwalder 
        <christoph.boehmwalder@...bit.com>,
        Steve French <smfrench@...il.com>,
        Philipp Reisner <philipp.reisner@...bit.com>,
        David Laight <David.Laight@...lab.com>,
        "Eric W. Biederman" <ebiederm@...ssion.com>
Subject: Re: [PATCH 4.9 183/271] signal: Allow cifs and drbd to receive their
 terminating signals

On Wed, Jan 29, 2020 at 12:36:43PM +0100, Greg Kroah-Hartman wrote:
>On Wed, Jan 29, 2020 at 12:10:47PM +0100, Thomas Voegtle wrote:
>> On Tue, 28 Jan 2020, Greg Kroah-Hartman wrote:
>>
>> > From: Eric W. Biederman <ebiederm@...ssion.com>
>> >
>> > [ Upstream commit 33da8e7c814f77310250bb54a9db36a44c5de784 ]
>> >
>> > My recent to change to only use force_sig for a synchronous events
>> > wound up breaking signal reception cifs and drbd.  I had overlooked
>> > the fact that by default kthreads start out with all signals set to
>> > SIG_IGN.  So a change I thought was safe turned out to have made it
>> > impossible for those kernel thread to catch their signals.
>> >
>> > Reverting the work on force_sig is a bad idea because what the code
>> > was doing was very much a misuse of force_sig.  As the way force_sig
>> > ultimately allowed the signal to happen was to change the signal
>> > handler to SIG_DFL.  Which after the first signal will allow userspace
>> > to send signals to these kernel threads.  At least for
>> > wake_ack_receiver in drbd that does not appear actively wrong.
>> >
>> > So correct this problem by adding allow_kernel_signal that will allow
>> > signals whose siginfo reports they were sent by the kernel through,
>> > but will not allow userspace generated signals, and update cifs and
>> > drbd to call allow_kernel_signal in an appropriate place so that their
>> > thread can receive this signal.
>> >
>> > Fixing things this way ensures that userspace won't be able to send
>> > signals and cause problems, that it is clear which signals the
>> > threads are expecting to receive, and it guarantees that nothing
>> > else in the system will be affected.
>> >
>> > This change was partly inspired by similar cifs and drbd patches that
>> > added allow_signal.
>> >
>> > Reported-by: ronnie sahlberg <ronniesahlberg@...il.com>
>> > Reported-by: Christoph Böhmwalder <christoph.boehmwalder@...bit.com>
>> > Tested-by: Christoph Böhmwalder <christoph.boehmwalder@...bit.com>
>> > Cc: Steve French <smfrench@...il.com>
>> > Cc: Philipp Reisner <philipp.reisner@...bit.com>
>> > Cc: David Laight <David.Laight@...LAB.COM>
>> > Fixes: 247bc9470b1e ("cifs: fix rmmod regression in cifs.ko caused by force_sig changes")
>> > Fixes: 72abe3bcf091 ("signal/cifs: Fix cifs_put_tcp_session to call send_sig instead of force_sig")
>>
>> These two commits come with that release, but...
>>
>> > Fixes: fee109901f39 ("signal/drbd: Use send_sig not force_sig")
>> > Fixes: 3cf5d076fb4d ("signal: Remove task parameter from force_sig")
>>
>> ...these two commits not and were never added to 4.9.y.
>>
>> Are these both really not needed?
>
>I don't think so, do you feel otherwise?

Both of those commits read as a cleanup to me. I've actually slightly
modified to patch to not need those commits (they were less than trivial
to backport as is).

-- 
Thanks,
Sasha