Re: [PATCH v2] can: kvaser_usb: leaf: Fix potential infinite loop in command parsers

[Jimmy Assarsson <extja@kvaser.com>]

On 10/29/25 20:06, Seungjin Bae wrote:
> Hello Jimmy,
> 
> Thank you for trying to reproduce the issue and for the detailed
> explanation of the firmware logic.
> 
> You are correct that this issue would not occur with the standard Kvaser
> firmware. The vulnerability I reported wasn’t found by running code
> on an actual Kvaser device.
> 
> Instead, I discovered this issue by performing analysis on the driver
> code using a symbolic execution tool. This tool demonstrated that
> the driver contains a vulnerable code path.
> 
> My goal was to show that if a malicious device is connected—one that
> sends a specifically crafted packet sequence not normally produced by
> the firmware—the driver code will process it incorrectly and cause
> the kernel panic.
> 
> So regretfully, I don’t have any hardware information yet.

Sorry, I overlooked the title, and assumed this was a problem you had
encountered with a real device.

Patch LGTM and tested OK with actual Kvaser devices:
Reviewed-by: Jimmy Assarsson <extja@kvaser.com>
Tested-by: Jimmy Assarsson <extja@kvaser.com>

Thanks!
/jimmy


> Thank you for your precious time.
> 
> Best,
> Seungjin Bae
> 
> 2025년 10월 29일 (수) 오전 6:53, Jimmy Assarsson <extja@kvaser.com 
> <mailto:extja@kvaser.com>>님이 작성:
> 
>     On 10/26/25 14:26, Jimmy Assarsson wrote:
>      > Hi Seungjin,
>      >
>      > Thanks for fixing this!
>      > I'll do some testing in the beginning of next week.
>      > Which Kvaser device did you use when you discovered the problem?
>      >
>      > Best regards,
>      > jimmy
> 
>     Hi Seungjin,
> 
>     I've not been able to reproduce this problem, when testing with the
>     latest firmware on multiple different devices.
> 
>     If the next command in the firmware packet queue, doesn't fit within the
>     current endpoint transaction (wMaxPacketSize), the firmware will
>     terminate the transaction with a zero byte. The driver then interprets
>     this as a zero-length command, and skip to the next transaction.
> 
>     The firmware is responsible to insert a "zero termination byte" only
>     when there is already one or more packets in the current transaction.
>     Since all commands have even lengths (4,8,10,12,16,20,24,30,32 bytes)
>     and the wMaxPacketSize is also even (64 bytes or 512 bytes, depending on
>     the device), I cannot see a situation where the zero termination byte
>     would be inserted exactly at the wMaxPacketSize boundary.
> 
>     Can you please provide which Kvaser device and firmware you use:
>         lsusb -d 0bfd:
>         ethtool -i can0
> 
>     Best regards,
>     jimmy