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net: introduce device min_header_len

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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.

Fixes: 9ed988cd59 ("packet: validate variable length ll headers")
Reported-by: Sowmini Varadhan <sowmini.varadhan@oracle.com>
Signed-off-by: Willem de Bruijn <willemb@google.com>
Acked-by: Eric Dumazet <edumazet@google.com>
Acked-by: Sowmini Varadhan <sowmini.varadhan@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Willem de Bruijn 2017-02-07 15:57:20 -05:00 committed by David S. Miller
parent d7426c69a1
commit 217e6fa24c
3 changed files with 6 additions and 0 deletions
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1
drivers/net/loopback.c
View File

@ -164,6 +164,7 @@ static void loopback_setup(struct net_device *dev)
{
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;

4
include/linux/netdevice.h
View File

@ -1511,6 +1511,7 @@ enum netdev_priv_flags {
* @max_mtu: Interface Maximum 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
@ -1728,6 +1729,7 @@ struct net_device {
unsigned int max_mtu;
unsigned short type;
unsigned short hard_header_len;
unsigned short min_header_len;
unsigned short needed_headroom;
unsigned short needed_tailroom;
@ -2694,6 +2696,8 @@ static inline bool dev_validate_header(const struct net_device *dev,
{
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);

1
net/ethernet/eth.c
View File

@ -356,6 +356,7 @@ 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->min_mtu = ETH_MIN_MTU;
dev->max_mtu = ETH_DATA_LEN;