linux-kernel - Re: UBSAN: Undefined behaviour in drivers/usb/core/devio.c:1517:25

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Message-ID: <56A798DB.8000200@virtuozzo.com>
Date:	Tue, 26 Jan 2016 19:03:39 +0300
From:	Andrey Ryabinin <aryabinin@...tuozzo.com>
To:	Alan Stern <stern@...land.harvard.edu>,
	Chris Bainbridge <chris.bainbridge@...il.com>
CC:	<linux-kernel@...r.kernel.org>, <aryabinin@...tuozzo.com>,
	<gregkh@...uxfoundation.org>, <linux-usb@...r.kernel.org>
Subject: Re: UBSAN: Undefined behaviour in drivers/usb/core/devio.c:1517:25

On 01/26/2016 06:25 PM, Alan Stern wrote:
> On Tue, 26 Jan 2016, Chris Bainbridge wrote:
> 
>> Booting 4.5.0-rc1 with new UBSAN checker enabled:
>>
>> [    4.556968] ================================================================================
>> [    4.556972] UBSAN: Undefined behaviour in drivers/usb/core/devio.c:1517:25
>> [    4.556975] shift exponent -1 is negative
> 
> Does a left shift by a negative amount matter if the result isn't used?
> 

By definition, any code with undefined behavior could do anything.
But in practice, undefined shift just leads to undefined result of shift operation
(it depends on operands and architecture).


> Alan Stern
>