On Tue, 2006-10-31 at 09:36 -0500, Vlad Yasevich wrote: > Herbert Xu wrote: > > Hi Sridhar: > > > > On Mon, Oct 30, 2006 at 05:31:24PM -0800, Sridhar Samudrala wrote: > >> I think we currently assume atleast the SCTP header and the data > >> chunk header to be in the skb head. > >> But we do handle skbs with data in the frag_list. > >> Not sure about skb's with paged fragments. > > > > You can't assume the chunk header to be in the head. Think about what > > happens when some malicious person sends you a fragmented SCTP packet. > > > >> Does XEN use frag_list or frags array? > > > > Xen creates paged frags in domU=>dom0 or domU=>domU traffic. > > Of course frag_list can always occur as a result of IP fragmentation. > > > >> Is there a simple way to simulate incoming packets with transport > >> headers and data in skb's frag_list/pages without having to use XEN. > > > > You can use IP fragments to create them. > > > > But the important thing is to work through the code. Basically wherever > > you see things like skb_pull/skb->data without a preceding pskb_may_pull > > call, then you have a problem. > > Wouldn't this in the end be equivalent to skb_linearize()? I am trying to > think of a way do things without reallocating too much memory. It will be equivalent only if you pass a skb->data_len as the length to pskb_may_pull(). However, pskb_may_pull() is generally called with much smaller lengths equal to a specific header length and it tries to copy the header from the fragments to skb->tail if there is enough room.
> > Yes, SCTP is really broken with regard to fragmented skbs. In fact, I > have a test case that will crash the lksctp at will when receiving an IP > fragmented > message. Because we support path mtu, we should not see ip fragmentation in general although it is possible if there is a change in path mtu during a transfer. So i guess you may be trying your test with path mtu disabled and with very small MTUs(< 500) or a packet with bundled chunks. > > The reason pskb_may_pull() is not a great solution IMO, is because we > may end up doing very large orders of allocations if someone decided to use > 9000 MTU > on the first hop. I can see things going bad on loopback with 16K MTU as > well. pskb_may_pull() should be used only to pull in the headers, not the entire message to the skb head. But with small messages that are bundled, this may get complicated. Thanks Sridhar - To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
