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net/packet: fix packet receive on L3 devices without visible hard header

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In the patchset merged by commit b9fcf0a0d8
("Merge branch 'support-AF_PACKET-for-layer-3-devices'") L3 devices which
did not have header_ops were given one for the purpose of protocol parsing
on af_packet transmit path.

That change made af_packet receive path regard these devices as having a
visible L3 header and therefore aligned incoming skb->data to point to the
skb's mac_header. Some devices, such as ipip, xfrmi, and others, do not
reset their mac_header prior to ingress and therefore their incoming
packets became malformed.

Ideally these devices would reset their mac headers, or af_packet would be
able to rely on dev->hard_header_len being 0 for such cases, but it seems
this is not the case.

Fix by changing af_packet RX ll visibility criteria to include the
existence of a '.create()' header operation, which is used when creating
a device hard header - via dev_hard_header() - by upper layers, and does
not exist in these L3 devices.

As this predicate may be useful in other situations, add it as a common
dev_has_header() helper in netdevice.h.

Fixes: b9fcf0a0d8 ("Merge branch 'support-AF_PACKET-for-layer-3-devices'")
Signed-off-by: Eyal Birger <eyal.birger@gmail.com>
Acked-by: Jason A. Donenfeld <Jason@zx2c4.com>
Acked-by: Willem de Bruijn <willemb@google.com>
Link: https://lore.kernel.org/r/20201121062817.3178900-1-eyal.birger@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Eyal Birger 2020-11-21 08:28:17 +02:00 committed by Jakub Kicinski
parent 2980cbd4dc
commit d549699048
2 changed files with 14 additions and 9 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

5
include/linux/netdevice.h
View File

@ -3137,6 +3137,11 @@ static inline bool dev_validate_header(const struct net_device *dev,
return false;
}
static inline bool dev_has_header(const struct net_device *dev)
{
return dev->header_ops && dev->header_ops->create;
}
typedef int gifconf_func_t(struct net_device * dev, char __user * bufptr,
int len, int size);
int register_gifconf(unsigned int family, gifconf_func_t *gifconf);

18
net/packet/af_packet.c
View File

@ -93,8 +93,8 @@
/*
Assumptions:
- If the device has no dev->header_ops, there is no LL header visible
above the device. In this case, its hard_header_len should be 0.
- If the device has no dev->header_ops->create, there is no LL header
visible above the device. In this case, its hard_header_len should be 0.
The device may prepend its own header internally. In this case, its
needed_headroom should be set to the space needed for it to add its
internal header.
@ -108,26 +108,26 @@
On receive:
-----------
Incoming, dev->header_ops != NULL
Incoming, dev_has_header(dev) == true
mac_header -> ll header
data -> data
Outgoing, dev->header_ops != NULL
Outgoing, dev_has_header(dev) == true
mac_header -> ll header
data -> ll header
Incoming, dev->header_ops == NULL
Incoming, dev_has_header(dev) == false
mac_header -> data
However drivers often make it point to the ll header.
This is incorrect because the ll header should be invisible to us.
data -> data
Outgoing, dev->header_ops == NULL
Outgoing, dev_has_header(dev) == false
mac_header -> data. ll header is invisible to us.
data -> data
Resume
If dev->header_ops == NULL we are unable to restore the ll header,
If dev_has_header(dev) == false we are unable to restore the ll header,
because it is invisible to us.
@ -2069,7 +2069,7 @@ static int packet_rcv(struct sk_buff *skb, struct net_device *dev,
skb->dev = dev;
if (dev->header_ops) {
if (dev_has_header(dev)) {
/* The device has an explicit notion of ll header,
* exported to higher levels.
*
@ -2198,7 +2198,7 @@ static int tpacket_rcv(struct sk_buff *skb, struct net_device *dev,
if (!net_eq(dev_net(dev), sock_net(sk)))
goto drop;
if (dev->header_ops) {
if (dev_has_header(dev)) {
if (sk->sk_type != SOCK_DGRAM)
skb_push(skb, skb->data - skb_mac_header(skb));
else if (skb->pkt_type == PACKET_OUTGOING) {