linux-kernel - Re: [PATCH 1/3] ser_gigaset: fix up NULL checks

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Date:	Tue, 8 Dec 2015 22:16:57 +0000
From:	One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>
To:	Paul Bolle <pebolle@...cali.nl>
Cc:	Tilman Schmidt <tilman@...p.cc>, netdev@...r.kernel.org,
	Peter Hurley <peter@...leysoftware.com>,
	Sasha Levin <sasha.levin@...cle.com>,
	syzkaller@...glegroups.com, David Miller <davem@...emloft.net>,
	Karsten Keil <isdn@...ux-pingi.de>,
	isdn4linux@...tserv.isdn4linux.de,
	gigaset307x-common@...ts.sourceforge.net,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] ser_gigaset: fix up NULL checks

> Should we backport this all the way to v2.6.32 (currently the oldest
> stable tree)?

We need to be able to explain how the case being tested can occur, then
explain the situation in which it actually prevents a race condition.

If nobody can do that then it shouldn't be backported because its change
without value and just risk. 

The right fix as far as I can see is to remove the tests although
WARN_ON() combined with your tty->ops change might be safer.

> It's pretty obvious that this should have been part of commit
>  f34d7a5b7010 ("tty: The big operations rework"). That being said, these

It ahould probably have been fixed around the same time or in one of the
tty locking reviews, but drivers/isdn and net/irda weren't traditionally
part of the general tty maintenance but handled separately/

> test puzzle me. It's not obvious why they're needed. Ie, can the null
> dereferences they try to catch really happen? But I can try to figure
> out that in the future, if I ever feel the urge to do so. Anyhow:
> 
> Acked-by: Paul Bolle <pebolle@...cali.nl>

Nacked-by: Alan Cox <alan@...ux.intel.com>
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