ipv4: allow local fragmentation in ip_finish_output_gso()

Some configurations (e.g. geneve interface with default
MTU of 1500 over an ethernet interface with 1500 MTU) result
in the transmission of packets that exceed the configured MTU.
While this should be considered to be a "bad" configuration,
it is still allowed and should not result in the sending
of packets that exceed the configured MTU.

Fix by dropping the assumption in ip_finish_output_gso() that
locally originated gso packets will never need fragmentation.
Basic testing using iperf (observing CPU usage and bandwidth)
have shown no measurable performance impact for traffic not
requiring fragmentation.

Fixes: c8b6e92431b1 ("net: ip: push gso skb forwarding handling down the stack")
Reported-by: Jan Tluka <jtluka@redhat.com>
Signed-off-by: Lance Richardson <lrichard@redhat.com>
Acked-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/include/net/ip.h b/include/net/ip.h
index 5413883ac47f0796a64e9f3792f3b785335cc837..d3a107850a41f0b4b62fedd4d0b88b20a45166b2 100644 (file)
--- a/include/net/ip.h
+++ b/include/net/ip.h
@@ -47,8 +47,7 @@ struct inet_skb_parm {
 #define IPSKB_REROUTED         BIT(4)
 #define IPSKB_DOREDIRECT       BIT(5)
 #define IPSKB_FRAG_PMTU                BIT(6)
-#define IPSKB_FRAG_SEGS                BIT(7)
-#define IPSKB_L3SLAVE          BIT(8)
+#define IPSKB_L3SLAVE          BIT(7)
 
        u16                     frag_max_size;
 };

diff --git a/net/ipv4/ip_forward.c b/net/ipv4/ip_forward.c
index 8b4ffd2168395b4d3b6ec67e166af13c122128ca..9f0a7b96646f368021d9cd51bc3f728ba49eed0d 100644 (file)
--- a/net/ipv4/ip_forward.c
+++ b/net/ipv4/ip_forward.c
@@ -117,7 +117,7 @@ int ip_forward(struct sk_buff *skb)
        if (opt->is_strictroute && rt->rt_uses_gateway)
                goto sr_failed;
 
-       IPCB(skb)->flags |= IPSKB_FORWARDED | IPSKB_FRAG_SEGS;
+       IPCB(skb)->flags |= IPSKB_FORWARDED;
        mtu = ip_dst_mtu_maybe_forward(&rt->dst, true);
        if (ip_exceeds_mtu(skb, mtu)) {
                IP_INC_STATS(net, IPSTATS_MIB_FRAGFAILS);

diff --git a/net/ipv4/ip_output.c b/net/ipv4/ip_output.c
index 03e7f7310423f7731ae0db7a40e7aae1a7598bb1..49714010ac2ecf688663c298cf35bc925406a07a 100644 (file)
--- a/net/ipv4/ip_output.c
+++ b/net/ipv4/ip_output.c
@@ -239,11 +239,9 @@ static int ip_finish_output_gso(struct net *net, struct sock *sk,
        struct sk_buff *segs;
        int ret = 0;
 
-       /* common case: fragmentation of segments is not allowed,
-        * or seglen is <= mtu
+       /* common case: seglen is <= mtu
         */
-       if (((IPCB(skb)->flags & IPSKB_FRAG_SEGS) == 0) ||
-             skb_gso_validate_mtu(skb, mtu))
+       if (skb_gso_validate_mtu(skb, mtu))
                return ip_finish_output2(net, sk, skb);
 
        /* Slowpath -  GSO segment length is exceeding the dst MTU.

diff --git a/net/ipv4/ip_tunnel_core.c b/net/ipv4/ip_tunnel_core.c
index 777bc1883870ec91d7c4df9adfde50fc3f384043..fed3d29f9eb3b716664b8d9eba052695cbb867bd 100644 (file)
--- a/net/ipv4/ip_tunnel_core.c
+++ b/net/ipv4/ip_tunnel_core.c
@@ -63,7 +63,6 @@ void iptunnel_xmit(struct sock *sk, struct rtable *rt, struct sk_buff *skb,
        int pkt_len = skb->len - skb_inner_network_offset(skb);
        struct net *net = dev_net(rt->dst.dev);
        struct net_device *dev = skb->dev;
-       int skb_iif = skb->skb_iif;
        struct iphdr *iph;
        int err;
 
@@ -73,16 +72,6 @@ void iptunnel_xmit(struct sock *sk, struct rtable *rt, struct sk_buff *skb,
        skb_dst_set(skb, &rt->dst);
        memset(IPCB(skb), 0, sizeof(*IPCB(skb)));
 
-       if (skb_iif && !(df & htons(IP_DF))) {
-               /* Arrived from an ingress interface, got encapsulated, with
-                * fragmentation of encapulating frames allowed.
-                * If skb is gso, the resulting encapsulated network segments
-                * may exceed dst mtu.
-                * Allow IP Fragmentation of segments.
-                */
-               IPCB(skb)->flags |= IPSKB_FRAG_SEGS;
-       }
-
        /* Push down and install the IP header. */
        skb_push(skb, sizeof(struct iphdr));
        skb_reset_network_header(skb);

diff --git a/net/ipv4/ipmr.c b/net/ipv4/ipmr.c
index 5f006e13de567ad65ce856a47c118f5ea91ac671..27089f5ebbb1c1c6e13038a94aeee5209e03d532 100644 (file)
--- a/net/ipv4/ipmr.c
+++ b/net/ipv4/ipmr.c
@@ -1749,7 +1749,7 @@ static void ipmr_queue_xmit(struct net *net, struct mr_table *mrt,
                vif->dev->stats.tx_bytes += skb->len;
        }
 
-       IPCB(skb)->flags |= IPSKB_FORWARDED | IPSKB_FRAG_SEGS;
+       IPCB(skb)->flags |= IPSKB_FORWARDED;
 
        /* RFC1584 teaches, that DVMRP/PIM router must deliver packets locally
         * not only before forwarding, but after forwarding on all output