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Commit 880621c2 authored Nov 22, 2015 by Martin Blumenstingl Committed by David S. Miller Nov 29, 2015

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

Commit 9c707762 ("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>

parent c9da161c

include/linux/netdevice.h

+2 −1

Original line number	Diff line number	Diff line
		@@ -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

net/packet/af_packet.c

+2 −2

Original line number	Diff line number	Diff line
		@@ -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;
		}