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

Commit 9c7077622dd91 ("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>

diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index 67bfac1abfc1ac8bd95bf3ddcf35aac07145166b..3b5d134e945a9b1a5dda9b636c04909318fe8a67 100644 (file)
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -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

diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
index 1cf928fb573e6769a4070327baa74adb300cde7e..992396aa635ce1174f6e62f19ae3f19a550668c6 100644 (file)
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -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;
        }