On Wed, May 07, 2014 at 10:07:09AM +0200, Michael Tuexen wrote: > On 07 May 2014, at 09:56, Yonghyeon PYUN <[email protected]> wrote: > > > On Sat, May 03, 2014 at 11:52:47AM +0200, Michael Tuexen wrote: > >> On 02 May 2014, at 16:02, Bjoern A. Zeeb <[email protected]> wrote: > >> > >>> > >>> On 02 May 2014, at 10:22 , Michael Tuexen > >>> <[email protected]> wrote: > >>> > >>>> Dear all, > >>>> > >>>> during testing I found that FreeBSD head (on a raspberry pi) accepts > >>>> SCTP packet > >>>> with bad checksums. After debugging this I figured out that this is a > >>>> problem with > >>>> the csum_flags defined in mbuf.h. > >>>> > >>>> The SCTP code on its input path checks for CSUM_SCTP_VALID, which is > >>>> defined in mbuf.h: > >>>> #define CSUM_SCTP_VALID CSUM_L4_VALID > >>>> This makes sense: If CSUM_SCTP_VALID is set in csum_flags, the packet is > >>>> considered > >>>> to have a correct checksum. > >>>> > >>>> For UDP and TCP some drivers calculate the UDP/TCP checksum and set > >>>> CSUM_DATA_VALID in > >>>> csum_flags to indicate that the UDP/TCP should consider csum_data to > >>>> figure out if > >>>> the packet has a correct checksum. The problem is that CSUM_DATA_VALID > >>>> is defined as > >>>> #define CSUM_DATA_VALID CSUM_L4_VALID > >>>> In this case the semantic is not that the packet has a valid checksum, > >>>> but the csum_data > >>>> field contains information. > >>>> > >>>> Now the following happens (on the raspberry pi the driver used is > >>>> dev/usb/net/if_smsc.c > >>>> > >>>> 1. A packet is received and if it is not too short, the checksum computed > >>>> is stored in csum_data and the flag CSUM_DATA_VALID is set. This happens > >>>> for all IP packets, not only for UDP and TCP packets. > >>>> 2. In case of SCTP packets, the SCTP interprets CSUM_DATA_VALID as > >>>> CSUM_SCTP_VALID > >>>> and accepts the packet. So no SCTP checksum check ever happened. > >>>> > >>>> Alternatives to fix this: > >>>> > >>>> 1. Change all drivers to set CSUM_DATA_VALID only in case of UDP or TCP > >>>> packets, since > >>>> it only makes sense in these cases. > >>> > >>> Wait, or for SCTP in cad the crc32 (I think it was) was actually checked > >>> but not otherwise. This is how it should be imho. It seems like a > >>> driver bug. > >> I went through the list of drivers and you are right, it seems to be a bug > >> in if_smsc.c. Most of the other drivers check for UDP/TCP, a small set I > >> can't tell. > >> > > > > I'm not sure how the controller computes TCP/UDP checksum values. > > It seems the publicly available data sheet was highly sanitized so > > it was useless to me. The comment in the driver says that the > Same for me... > > controller computes RX checksum after the IPv4 header to the end of > > ethernet frame. After seeing that comment, three questions popped > > up: > > > > 1. Is the controller smart enough to skip IP options header in > > TCP/UDP checksum offloading? > > 2. How controller handles UDP checksum value 0x0000(i.e. sender > > didn't compute UDP checksum)? > > 3. How the controller can compute TCP checksum of fragmented > > packets? > > > > Since you have the controller I guess it's easy to verify all > > cases. For case 3, I believe the controller can't handle > > fragmented frames so driver should have to explicitly check ip_off > > field of IPv4 header. See how gem(4)/sk(4)/hme(4) and fxp(4) > > handle it. > Let me check this. Is there a tool to send UDP/TCP with IP level options > or do I need to write a small test program myself? >
I recall I used buggy ipsend of ipfilter package in the past but it would be more easy to write a simple test program or patch driver to generate those frames. _______________________________________________ [email protected] mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-net To unsubscribe, send any mail to "[email protected]"
