[PATCH 4.14 01/64] gso_segment: Reset skb->mac_len after modifying network header

From: Greg Kroah-Hartman
Date: Thu Sep 27 2018 - 05:16:35 EST


4.14-stable review patch. If anyone has any objections, please let me know.

------------------

From: "Toke Hød-Jøsen" <toke@xxxxxxx>

[ Upstream commit c56cae23c6b167acc68043c683c4573b80cbcc2c ]

When splitting a GSO segment that consists of encapsulated packets, the
skb->mac_len of the segments can end up being set wrong, causing packet
drops in particular when using act_mirred and ifb interfaces in
combination with a qdisc that splits GSO packets.

This happens because at the time skb_segment() is called, network_header
will point to the inner header, throwing off the calculation in
skb_reset_mac_len(). The network_header is subsequently adjust by the
outer IP gso_segment handlers, but they don't set the mac_len.

Fix this by adding skb_reset_mac_len() calls to both the IPv4 and IPv6
gso_segment handlers, after they modify the network_header.

Many thanks to Eric Dumazet for his help in identifying the cause of
the bug.

Acked-by: Dave Taht <dave.taht@xxxxxxxxx>
Reviewed-by: Eric Dumazet <edumazet@xxxxxxxxxx>
Signed-off-by: Toke HÃiland-JÃrgensen <toke@xxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
net/ipv4/af_inet.c | 1 +
net/ipv6/ip6_offload.c | 1 +
2 files changed, 2 insertions(+)

--- a/net/ipv4/af_inet.c
+++ b/net/ipv4/af_inet.c
@@ -1307,6 +1307,7 @@ struct sk_buff *inet_gso_segment(struct
if (encap)
skb_reset_inner_headers(skb);
skb->network_header = (u8 *)iph - skb->head;
+ skb_reset_mac_len(skb);
} while ((skb = skb->next));

out:
--- a/net/ipv6/ip6_offload.c
+++ b/net/ipv6/ip6_offload.c
@@ -113,6 +113,7 @@ static struct sk_buff *ipv6_gso_segment(
payload_len = skb->len - nhoff - sizeof(*ipv6h);
ipv6h->payload_len = htons(payload_len);
skb->network_header = (u8 *)ipv6h - skb->head;
+ skb_reset_mac_len(skb);

if (udpfrag) {
int err = ip6_find_1stfragopt(skb, &prevhdr);