On 11/11/2015 12:24 AM, Willem de Bruijn wrote:
On Tue, Nov 10, 2015 at 6:12 PM, Daniel Borkmann <dan...@iogearbox.net> wrote:
On 11/10/2015 11:52 PM, Willem de Bruijn wrote:
if (sock->type == SOCK_DGRAM) {
- err = dev_hard_header(skb, dev, ntohs(proto), addr,
- NULL, tp_len);
+ /* In DGRAM sockets, we expect struct sockaddr_ll was
filled
+ * via struct msghdr, so we have dest mac and
skb->protocol.
+ * Otherwise there's not too much useful things we can do
in
+ * this flush run.
+ */
+ err = dev_hard_header(skb, dev, ntohs(skb->protocol),
addr,
+ NULL, tp_len);
This change is not really necessary.
Sure agreed, I found it helpful though. Don't mind removing it.
if (unlikely(err < 0))
return -EINVAL;
- } else if (dev->hard_header_len) {
Why remove the check on hard_header_len?
Hmm, the patch doesn't remove the check (it's moved further below).
- if (ll_header_truncated(dev, tp_len))
- return -EINVAL;
+ } else {
+ /* If skb->protocol is still 0, try to infer/guess it.
Might
+ * not be fully reliable in the sense that a user could
still
+ * change/race data afterwards, but on the other hand the
proto
The race goes away when probing it after the copy in skb_store_bits.
Then it is also certain that tp_len is long enough to hold the entire
link layer header.
The skb_store_bits() is only done in case we do have a dev->hard_header_len
or in case where we run into a possible situation where we have the
additional
4 bytes on a full frame. In that case we need to check them properly, which
requires copying, otherwise we don't copy any header.
I assumed that hard_header_len has to be non-zero if there
is a link layer header to probe. If we only intend to implement
probing in the case of Ethernet, then it certainly holds.
Yeah, I guess we only care about ether_setup() alike devices, so we'd have
ETH_HLEN room as dev->hard_header_len. That will hold, yes.
+ * can be set arbitrarily anyways. We only need to take
care
+ * in case of extra large VLAN frames.
+ */
+ if (!skb->protocol && tp_len >= ETH_HLEN)
+ skb->protocol = ((struct ethhdr *)data)->h_proto;
Packet sockets are not restricted to link layer of type Ethernet.
There are a few other points in this file that also cast mac header
to eth_hdr(skb).
Ok, the set doesn't address this assumption which we have elsewhere, too.
Do you suggest to also check on dev->type for these cases?
Yes. If I'm right, then the other cases have to be fixed, too. One of the
eth_hdr(skb) calls was introduced by patch 09effa67a18d, where the
deleted code shows how it is safely restricted to ethernet:
- if (dev->type == ARPHRD_ETHER) {
- skb->protocol = eth_type_trans(skb, dev);
- if (skb->protocol == htons(ETH_P_8021Q))
Saw that, so we need the check as one more fix for 57f89bfa2140 ("network:
Allow af_packet to transmit +4 bytes for VLAN packets.") as well.
I'll see to respin a v3 tomorrow.
Thanks,
Daniel
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