bnx2x: disable GSO where gso_size is too big for hardware

BugLink: https://bugs.launchpad.net/bugs/1715519
CVE-2018-1000026

If a bnx2x card is passed a GSO packet with a gso_size larger than
~9700 bytes, it will cause a firmware error that will bring the card
down:

bnx2x: [bnx2x_attn_int_deasserted3:4323(enP24p1s0f0)]MC assert!
bnx2x: [bnx2x_mc_assert:720(enP24p1s0f0)]XSTORM_ASSERT_LIST_INDEX 0x2
bnx2x: [bnx2x_mc_assert:736(enP24p1s0f0)]XSTORM_ASSERT_INDEX 0x0 = 0x00000000 0x25e43e47 0x00463e01 0x00010052
bnx2x: [bnx2x_mc_assert:750(enP24p1s0f0)]Chip Revision: everest3, FW Version: 7_13_1
... (dump of values continues) ...

Detect when the mac length of a GSO packet is greater than the maximum
packet size (9700 bytes) and disable GSO.
Signed-off-by: Daniel Axtens <dja@axtens.net>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
(cherry picked from commit 8914a595)
[nb: the reference to BY_FRAGS does not apply here, it was added in
     4.8]
Signed-off-by: Daniel Axtens <daniel.axtens@canonical.com>
Acked-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>
Acked-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>

drivers/net/ethernet/broadcom/bnx2x/bnx2x_main.c

@@ -12809,6 +12809,24 @@ static netdev_features_t bnx2x_features_check(struct sk_buff *skb,
 					      struct net_device *dev,
 					      netdev_features_t features)
 {
+	/*
+	 * A skb with gso_size + header length > 9700 will cause a
+	 * firmware panic. Drop GSO support.
+	 *
+	 * Eventually the upper layer should not pass these packets down.
+	 *
+	 * For speed, if the gso_size is <= 9000, assume there will
+	 * not be 700 bytes of headers and pass it through. Only do a
+	 * full (slow) validation if the gso_size is > 9000.
+	 *
+	 * (Due to the way SKB_BY_FRAGS works this will also do a full
+	 * validation in that case.)
+	 */
+	if (unlikely(skb_is_gso(skb) &&
+		     (skb_shinfo(skb)->gso_size > 9000) &&
+		     !skb_gso_validate_mac_len(skb, 9700)))
+		features &= ~NETIF_F_GSO_MASK;
+
 	features = vlan_features_check(skb, features);
 	return vxlan_features_check(skb, features);
 }