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packet: Allow packets with only a header (but no payload)

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Commit 9c7077622d ("packet: make packet_snd fail on len smaller
than l2 header") added validation for the packet size in packet_snd.
This change enforces that every packet needs a header (with at least
hard_header_len bytes) plus a payload with at least one byte. Before
this change the payload was optional.

This fixes PPPoE connections which do not have a "Service" or
"Host-Uniq" configured (which is violating the spec, but is still
widely used in real-world setups). Those are currently failing with the
following message: "pppd: packet size is too short (24 <= 24)"

Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Martin Blumenstingl 2015-11-22 17:46:09 +01:00 committed by David S. Miller
parent c9da161c65
commit 880621c260
2 changed files with 4 additions and 3 deletions
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3
include/linux/netdevice.h
View file

@ -1398,7 +1398,8 @@ enum netdev_priv_flags {
* @dma: DMA channel
* @mtu: Interface MTU value
* @type: Interface hardware type
* @hard_header_len: Hardware header length
* @hard_header_len: Hardware header length, which means that this is the
* minimum size of a packet.
*
* @needed_headroom: Extra headroom the hardware may need, but not in all
* cases can this be guaranteed

4
net/packet/af_packet.c
View file

@ -2329,8 +2329,8 @@ static void tpacket_destruct_skb(struct sk_buff *skb)
static bool ll_header_truncated(const struct net_device *dev, int len)
{
/* net device doesn't like empty head */
if (unlikely(len <= dev->hard_header_len)) {
net_warn_ratelimited("%s: packet size is too short (%d <= %d)\n",
if (unlikely(len < dev->hard_header_len)) {
net_warn_ratelimited("%s: packet size is too short (%d < %d)\n",
current->comm, len, dev->hard_header_len);
return true;
}