From: Greg KH <greg@kroah.com>
To: Changming Liu <liu.changm@northeastern.edu>
Cc: "thomas@winischhofer.net" <thomas@winischhofer.net>,
"linux-usb@vger.kernel.org" <linux-usb@vger.kernel.org>,
"Lu, Long" <l.lu@northeastern.edu>,
"yaohway@gmail.com" <yaohway@gmail.com>
Subject: Re: [Bug Report] drivers/usb/misc/sisusbvga: undefined result when left shift a possible negative value in sisusb_write_mem_bulk
Date: Wed, 20 May 2020 07:01:55 +0200 [thread overview]
Message-ID: <20200520050155.GB2105777@kroah.com> (raw)
In-Reply-To: <BL0PR06MB4548D5526F5BFAD528039FECE5B60@BL0PR06MB4548.namprd06.prod.outlook.com>
On Wed, May 20, 2020 at 03:51:04AM +0000, Changming Liu wrote:
> Hi Greg and Thomas,
> Greetings, I'm a first-year PhD student who is interested in the usage of UBSan for linux. And after some experiments, I've found that in drivers/usb/misc/sisusbvga/sisusb.c
> function sisusb_write_mem_bulk, there is an undefined behavior caused by left shifting a possible negative number.
>
> More specifically, in the switch statement for case 3, after executing copy_from_user, the the lower 3 bytes of char buf[4] are filled with data from user space.
> And these 3 bytes are left shifted accordingly to form a 32bit unsigned integer, swap32.
>
> The potential problem is, since the buf is declared as signed char buffer so each byte might be a negative number while being left shifted. According to the C standard, when the left-hand operand of the left shift operator is a negative value, the result is undefined. So I guess change the buf declaration to unsigned will help? Given that it's only used here.
Sounds like a good idea, patches are welcome to fix this.
thanks,
greg k-h
prev parent reply other threads:[~2020-05-20 5:02 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-20 3:51 [Bug Report] drivers/usb/misc/sisusbvga: undefined result when left shift a possible negative value in sisusb_write_mem_bulk Changming Liu
2020-05-20 5:01 ` Greg KH [this message]
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