net: introduce device min_header_len

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: 9ed988cd5915 ("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>

diff --git a/drivers/net/loopback.c b/drivers/net/loopback.c
index 1e05b7c2d157a22e06d115bcdd1d268876be03a7..0844f849641346b092e83923c1d196709b355e4c 100644 (file)
--- a/drivers/net/loopback.c
+++ b/drivers/net/loopback.c
@@ -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;

diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index 70ad0291d517b41cd1d4a3c2c7fc046f13e27980..27914672602d9d573e6a3da271cec33ccef51b16 100644 (file)
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -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);

diff --git a/net/ethernet/eth.c b/net/ethernet/eth.c
index 8c5a479681ca9ed8c2686208fc570e819a4db31a..516c87e75de7009e9e4f0cbdc80f8160c318fdf4 100644 (file)
--- a/net/ethernet/eth.c
+++ b/net/ethernet/eth.c
@@ -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;