Patch "net: introduce device min_header_len" has been added to the 4.4-stable tree

This is a note to let you know that I've just added the patch titled

net: introduce device min_header_len

to the 4.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
net-introduce-device-min_header_len.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Willem de Bruijn <[email protected]>
Date: Tue, 7 Feb 2017 15:57:20 -0500
Subject: net: introduce device min_header_len

From: Willem de Bruijn <[email protected]>

[ Upstream commit 217e6fa24ce28ec87fca8da93c9016cb78028612 ]

The stack must not pass packets to device drivers that are shorter than the minimum link layer header length.

Previously, packet sockets would drop packets smaller than or equal to dev->hard_header_len, but this has false positives. Zero length payload is used over Ethernet. Other link layer protocols support variable length headers. Support for validation of these protocols removed the min length check for all protocols.

Introduce an explicit dev->min_header_len parameter and drop all packets below this value. Initially, set it to non-zero only for Ethernet and loopback. Other protocols can follow in a patch to net-next.

---
 drivers/net/loopback.c    |    1 +
 include/linux/netdevice.h |    4 ++++
 net/ethernet/eth.c        |    1 +
 3 files changed, 6 insertions(+)

@@ -164,6 +164,7 @@ static void loopback_setup(struct net_de
 {
 	dev->mtu		= 64 * 1024;
 	dev->hard_header_len	= ETH_HLEN;	/* 14	*/
+	dev->min_header_len	= ETH_HLEN;	/* 14	*/
 	dev->addr_len		= ETH_ALEN;	/* 6	*/
 	dev->type		= ARPHRD_LOOPBACK;	/* 0x0001*/
 	dev->flags		= IFF_LOOPBACK;

@@ -1399,6 +1399,7 @@ enum netdev_priv_flags {
  *	@mtu:		Interface MTU value
  *	@type:		Interface hardware type
  *	@hard_header_len: Maximum hardware header length.
+ *	@min_header_len:  Minimum hardware header length
  *
  *	@needed_headroom: Extra headroom the hardware may need, but not in all
  *			  cases can this be guaranteed

@@ -1619,6 +1620,7 @@ struct net_device {
 	unsigned int		mtu;
 	unsigned short		type;
 	unsigned short		hard_header_len;
+	unsigned short		min_header_len;
 
 	unsigned short		needed_headroom;
 	unsigned short		needed_tailroom;

@@ -2541,6 +2543,8 @@ static inline bool dev_validate_header(c
 {
 	if (likely(len >= dev->hard_header_len))
 		return true;
+	if (len < dev->min_header_len)
+		return false;
 
 	if (capable(CAP_SYS_RAWIO)) {
 		memset(ll_header + len, 0, dev->hard_header_len - len);

@@ -353,6 +353,7 @@ void ether_setup(struct net_device *dev)
 	dev->header_ops		= &eth_header_ops;
 	dev->type		= ARPHRD_ETHER;
 	dev->hard_header_len 	= ETH_HLEN;
+	dev->min_header_len	= ETH_HLEN;
 	dev->mtu		= ETH_DATA_LEN;
 	dev->addr_len		= ETH_ALEN;
 	dev->tx_queue_len	= 1000;	/* Ethernet wants good queues */

Patches currently in stable-queue which might be from [email protected] are

queue-4.4/packet-round-up-linear-to-header-len.patch queue-4.4/tun-read-vnet_hdr_sz-once.patch queue-4.4/ipv6-fix-ip6_tnl_parse_tlv_enc_lim.patch queue-4.4/net-introduce-device-min_header_len.patch queue-4.4/macvtap-read-vnet_hdr_size-once.patch