linux-kernel - Re: [PATCH] btusb: fix overflow return values

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Message-ID: <20130709025501.GA6369@adam-laptop>
Date:	Tue, 9 Jul 2013 10:55:01 +0800
From:	Adam Lee <adam.lee@...onical.com>
To:	Marcel Holtmann <marcel@...tmann.org>
Cc:	linux-bluetooth@...r.kernel.org,
	Wen-chien Jesse Sung <jesse.sung@...onical.com>,
	AceLan Kao <acelan.kao@...onical.com>,
	Tedd Ho-Jeong An <tedd.an@...el.com>,
	Anthony Wong <anthony.wong@...onical.com>,
	Gustavo Padovan <gustavo@...ovan.org>,
	Johan Hedberg <johan.hedberg@...il.com>,
	open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] btusb: fix overflow return values

On Mon, Jul 08, 2013 at 11:50:54AM -0700, Marcel Holtmann wrote:
> Hi Adam,
> 
> > PTR_ERR() returns a long type value, but btusb_setup_intel() and
> > btusb_setup_intel_patching() should return an int type value.
> > 
> > This bug makes the judgement "if (ret < 0)" not working on x86_64
> > architecture systems, leading to failure as below, even panic.
> > ...
> > For not affecting other modules, I choose to modify the return values
> > but not extend btusb_setup_intel() and btusb_setup_intel_patching()'s
> > return types. This is harmless, because the return values were only
> > used to comparing number 0.
> 
> there are tons of examples in various subsystems and drivers where we
> return PTR_ERR from a function calls returning int.
> 
> So I wonder what is actually going wrong here. If this is x86_64
> specific problem with PTR_ERR vs int, then we should have this problem
> everywhere in the kernel.

Hi, Marcel

I see you point, the difference between here and other subsystems are:

1, it returns -PTR_ERR() here but all other places return PTR_ERR(), I
checked.
2, the judgement is "if (ret < 0)" here but other places are "if (ret)".

I'm not saying other subsystems are 100% right, but here, returning
-PTR_ERR() and checking "if (ret < 0)" make the judgement broken much
much more easily.

I attached a testing C file, run it on x86_64, you will see the bug.

PS, about other subsystems, I also think returning PTR_ERR() from a
function calls returning int considered harmful sometimes, will talk
about that in other thread.

Great thanks.

-- 
Regards,
Adam Lee
Hardware Enablement

View attachment "ptr_err.c" of type "text/x-csrc" (607 bytes)