site_archiver@lists.apple.com Delivered-To: darwin-kernel@lists.apple.com On Dec 20, 2006, at 8:37 PM, Bhavesh Davda wrote: Thanks, Adi, So how do I do the workaround (byte-swap ip->ip_len in iff_output_func before calling mbuf_outbound_finalize, and then byte-swap it back), in a "future proof" way, so I don't have to reverse this workaround when Apple fixes the bug? In theory you won't have to do anything; the stack should detect if the length has been reversed by the filter and internally do the byte-swap (from network to host) only if necessary prior to calculating the transport checksum. Likewise, it will do the host to network byte-swap of that value (internally) for the IP header checksum calculation. In any case, the length in the IP header of the packet will be restored to what the filter has set it prior to calling the routine, upon return. That way the packet won't end up incorrect should the filter reverses the length back to network byte-order prior to sending it down. With the fix in place, the only redundant work done by your filter would then be the IP header checksum calculation though it shouldn't cost too much when compared to the cost of checksumming the payload. (I.e. without the fix, this step is necessary. With the fix, it's not, but it won't hurt as long as your code does the right computation.) Adi Or the fact that my NKE has to work on both older and newer kernels? Thanks! - Bhavesh On Dec 20, 2006, at 6:17 PM, Bhavesh Davda wrote: This is a known bug and a fix is already in order. Assuming that you call this from an interface filter, and that only the transport checksum is to be recomputed, you should be able to byte-swap the IP length, call mbuf_outbound_finalize() and restore the IP length back to the network-byte order. If the driver offloads IP header checksumming, and if this is an IPv4 packet, then you would need to recompute the IP header checksum yourself prior to sending the packet downstream. Once the fix is made available, you will no longer need to do any of the above. (Also note that this issue does not exist for PPC.) Adi _______________________________________________ Do not post admin requests to the list. They will be ignored. Darwin-kernel mailing list (Darwin-kernel@lists.apple.com) Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/darwin-kernel/site_archiver%40lists.a... This email sent to site_archiver@lists.apple.com On 12/20/06, Adi Masputra <adi@apple.com> wrote:

When calling mbuf_outbound_finalize() to compute the incomplete

TCP/UDP checksums on the mbuf from my iff_output_func (interface

filter output function), I kept getting messages from the kernel

"cksum: out of data".

Looking at the xnu-792.13.8 source, it looks like the underlying

in_cksum_skip, called from in_delayed_cksum_offset, expects the ip_len

field in the IP header to be in host-byte-order, while in reality the

mbuf handed to my iff_output_func had the ip_len field in the IP

header correctly populated in network-byte-order.

What is my iff_output_func to do in such a situation?

Thanks!

--

Bhavesh P. Davda

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