On Fri, Aug 31, 2012 at 01:59:04PM +0200, Wolfram Sang wrote:

Hi,

I just noticed today that commit c7cd606f60e7679c7f9eee7010f02a6f000209c1
("can: Fix data length code handling in rx path") says regarding
overlong packets:

===

The ISO 11898-1 Chapter 8.4.2.3 (DLC field) says that register values > 8
should be reduced to 8 without any error reporting or frame drop.

===

and this is why get_can_dlc() came into existance.

However, functions like can_dropped_invalid_skb() from dev.h or can_rcv() from
af_can.c do check for a correct length, but drop the packet in the error case.
Don't those need to be fixed?

Regards,

   Wolfram

Interesting point. My first idea is to acknowledge your thinking, BUT:
* ISO 11898-1 is about the wire format, whereas your issues address
  higher level interfaces. Higher level interfaces may IMHO use a stricter
  format that the wire format.
* I find it very likely that DLC is normalized in user space.
  This could prevent a lot of confusion in userspace apps.
  We could now argue on the best place to do normalization, but device drivers
  seem the best place.
* With CAN-FD in mind, the handling of DLC is stricter anyway. DLC > 8 is allowed,
  but is a real coding (probably), so we decided to communicate a 'len' field
  to userspace.

Does this address your concerns?

Kind regards,
Kurt