On Wednesday September 5, [EMAIL PROTECTED] wrote:
> On Wednesday August 22, [EMAIL PROTECTED] wrote:
> > Chuck Ebbert <[EMAIL PROTECTED]> wrote:
> > > https://bugzilla.redhat.com/bugzilla/show_bug.cgi?id=253290
> > >
> > > 18:57:54 osama kernel: [<c05be67f>] kernel_recvmsg+0x31/0x40
> > > 18:57:54 osama kernel: [<e0bc52d4>] svc_udp_recvfrom+0x114/0x368 [sunrpc]
> >
> > svc_udp_recvfrom is calling kernel_recvmsg with iov == NULL.
>
> iov == NULL used to work.
>
> I think it stopped working at
> commit 759e5d006462d53fb708daa8284b4ad909415da1
>
> Previously, as len==0, MSG_TRUNC would get set, so copy_only would get
> set, so skb_copy_datagram_iovec would get called, and that handles a
> len of 0.
>
> Now, skb_copy_and_csum_datagram_iovec gets called unless
> skb_csum_unnecessary(skb), which now kills us.
Actually, the new code is broken for more reasons than that.
In core/datagram.c, the comment for skb_copy_and_csum_datagram_iovec,
it says:
* Caller _must_ check that skb will fit to this iovec.
but udp_recvmsg doesn't.
It seems to try:
if (copied < ulen || UDP_SKB_CB(skb)->partial_cov) {
if (udp_lib_checksum_complete(skb))
goto csum_copy_err;
}
if (skb_csum_unnecessary(skb))
err = skb_copy_datagram_iovec(skb, sizeof(struct udphdr),
msg->msg_iov, copied );
so it doesn't call skb_copy_datagram_iovec if "copied < ulen".
However earlier there is:
ulen = skb->len - sizeof(struct udphdr);
copied = len;
if (copied > ulen)
copied = ulen;
so if the 'len' (of the iovec) is too small, we end up with "copied == ulen",
so udp_lib_checksum_complete doesn't get called....
>
> We could 'fix' it by making skb_copy_and_csum_datagram_iovec just
> return if len==0, or don't call it from udp_recvmsg in that case.
>
So the latter of these is needed.
NeilBrown
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