On Fri, 2016-02-26 at 12:33 -0500, Willem de Bruijn wrote: > On Fri, Feb 26, 2016 at 9:44 AM, Alan Cox <a...@linux.intel.com> > wrote: > > On Thu, 2016-02-25 at 15:26 -0500, David Miller wrote: > > > From: Heikki Hannikainen <he...@hes.iki.fi> > > > Date: Thu, 25 Feb 2016 21:36:07 +0200 (EET) > > > > > > > Commit 9c7077622dd9174 added a check, ll_header_truncated(), > > > > which > > > > requires that a packet transmitted using sendmsg() with > > > > PF_PACKET, > > > > SOCK_RAW must be longer than dev->hard_header_len. > > > > > > Fixed by: > > > > > > commit 880621c2605b82eb5af91a2c94223df6f5a3fb64 > > > Author: Martin Blumenstingl <martin.blumensti...@googlemail.com> > > > Date: Sun Nov 22 17:46:09 2015 +0100 > > > > > > packet: Allow packets with only a header (but no payload) > > > > The AX.25 case the header is variable length so this still doesn't > > fix > > the regression as far as I can see. > > Right. The simplest, if hacky, fix is to add something along the > lines of > > static unsigned short netdev_min_hard_header_len(struct net_device > *dev) > { > if (unlikely(dev->type ==ARPHDR_AX25)) > return AX25_KISS_HEADER_LEN; > else > return dev->hard_header_len; > }
AX.25 is not unique in this. Also there are protocols where the minimum header length for a valid raw frame is not the same as the minimum sized header for encapsulation of an IP frame because the IP frame is encapsulated with an extra header block. > Depending on how the variable encoding scheme works, a basic min > > length check may still produce buggy headers that confuse the stack > or > driver. I need to read up on AX25. If so, then extending header_ops > with an optional validate() function is a more generic approach of > checking header sanity. A validate() method is doable for NetROM, AX.25 and friends. So something like if (likely(len >= dev->hard_header_len)) return good; if (proto->validate && proto->validate(skb)) return good; return bad; works for amateur radio at least, and I think could be extended ok for any other cases like tunnels. Alan