openvswitch: Fix setting ipv6 fields causing hw csum failure

Ipv6 ttl, label and tos fields are modified without first
pulling/pushing the ipv6 header, which would have updated
the hw csum (if available). This might cause csum validation
when sending the packet to the stack, as can be seen in
the trace below.

Fix this by updating skb->csum if available.

Trace resulted by ipv6 ttl dec and then sending packet
to conntrack [actions: set(ipv6(hlimit=63)),ct(zone=99)]:
[295241.900063] s_pf0vf2: hw csum failure
[295241.923191] Call Trace:
[295241.925728]  <IRQ>
[295241.927836]  dump_stack+0x5c/0x80
[295241.931240]  __skb_checksum_complete+0xac/0xc0
[295241.935778]  nf_conntrack_tcp_packet+0x398/0xba0 [nf_conntrack]
[295241.953030]  nf_conntrack_in+0x498/0x5e0 [nf_conntrack]
[295241.958344]  __ovs_ct_lookup+0xac/0x860 [openvswitch]
[295241.968532]  ovs_ct_execute+0x4a7/0x7c0 [openvswitch]
[295241.979167]  do_execute_actions+0x54a/0xaa0 [openvswitch]
[295242.001482]  ovs_execute_actions+0x48/0x100 [openvswitch]
[295242.006966]  ovs_dp_process_packet+0x96/0x1d0 [openvswitch]
[295242.012626]  ovs_vport_receive+0x6c/0xc0 [openvswitch]
[295242.028763]  netdev_frame_hook+0xc0/0x180 [openvswitch]
[295242.034074]  __netif_receive_skb_core+0x2ca/0xcb0
[295242.047498]  netif_receive_skb_internal+0x3e/0xc0
[295242.052291]  napi_gro_receive+0xba/0xe0
[295242.056231]  mlx5e_handle_rx_cqe_mpwrq_rep+0x12b/0x250 [mlx5_core]
[295242.062513]  mlx5e_poll_rx_cq+0xa0f/0xa30 [mlx5_core]
[295242.067669]  mlx5e_napi_poll+0xe1/0x6b0 [mlx5_core]
[295242.077958]  net_rx_action+0x149/0x3b0
[295242.086762]  __do_softirq+0xd7/0x2d6
[295242.090427]  irq_exit+0xf7/0x100
[295242.093748]  do_IRQ+0x7f/0xd0
[295242.096806]  common_interrupt+0xf/0xf
[295242.100559]  </IRQ>
[295242.102750] RIP: 0033:0x7f9022e88cbd
[295242.125246] RSP: 002b:00007f9022282b20 EFLAGS: 00000246 ORIG_RAX: ffffffffffffffda
[295242.132900] RAX: 0000000000000005 RBX: 0000000000000010 RCX: 0000000000000000
[295242.140120] RDX: 00007f9022282ba8 RSI: 00007f9022282a30 RDI: 00007f9014005c30
[295242.147337] RBP: 00007f9014014d60 R08: 0000000000000020 R09: 00007f90254a8340
[295242.154557] R10: 00007f9022282a28 R11: 0000000000000246 R12: 0000000000000000
[295242.161775] R13: 00007f902308c000 R14: 000000000000002b R15: 00007f9022b71f40

Fixes: 3fdbd1ce ("openvswitch: add ipv6 'set' action")
Signed-off-by: Paul Blakey <paulb@nvidia.com>
Link: https://lore.kernel.org/r/20220223163416.24096-1-paulb@nvidia.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

include/net/checksum.h

@@ -142,6 +142,11 @@ static __always_inline void csum_replace2(__sum16 *sum, __be16 old, __be16 new)
 	*sum = ~csum16_add(csum16_sub(~(*sum), old), new);
 }
 
+static inline void csum_replace(__wsum *csum, __wsum old, __wsum new)
+{
+	*csum = csum_add(csum_sub(*csum, old), new);
+}
+
 struct sk_buff;
 void inet_proto_csum_replace4(__sum16 *sum, struct sk_buff *skb,
 			      __be32 from, __be32 to, bool pseudohdr);

net/openvswitch/actions.c

@@ -423,12 +423,43 @@ static void set_ipv6_addr(struct sk_buff *skb, u8 l4_proto,
 	memcpy(addr, new_addr, sizeof(__be32[4]));
 }
 
-static void set_ipv6_fl(struct ipv6hdr *nh, u32 fl, u32 mask)
+static void set_ipv6_dsfield(struct sk_buff *skb, struct ipv6hdr *nh, u8 ipv6_tclass, u8 mask)
 {
+	u8 old_ipv6_tclass = ipv6_get_dsfield(nh);
+
+	ipv6_tclass = OVS_MASKED(old_ipv6_tclass, ipv6_tclass, mask);
+
+	if (skb->ip_summed == CHECKSUM_COMPLETE)
+		csum_replace(&skb->csum, (__force __wsum)(old_ipv6_tclass << 12),
+			     (__force __wsum)(ipv6_tclass << 12));
+
+	ipv6_change_dsfield(nh, ~mask, ipv6_tclass);
+}
+
+static void set_ipv6_fl(struct sk_buff *skb, struct ipv6hdr *nh, u32 fl, u32 mask)
+{
+	u32 ofl;
+
+	ofl = nh->flow_lbl[0] << 16 |  nh->flow_lbl[1] << 8 |  nh->flow_lbl[2];
+	fl = OVS_MASKED(ofl, fl, mask);
+
 	/* Bits 21-24 are always unmasked, so this retains their values. */
-	OVS_SET_MASKED(nh->flow_lbl[0], (u8)(fl >> 16), (u8)(mask >> 16));
-	OVS_SET_MASKED(nh->flow_lbl[1], (u8)(fl >> 8), (u8)(mask >> 8));
-	OVS_SET_MASKED(nh->flow_lbl[2], (u8)fl, (u8)mask);
+	nh->flow_lbl[0] = (u8)(fl >> 16);
+	nh->flow_lbl[1] = (u8)(fl >> 8);
+	nh->flow_lbl[2] = (u8)fl;
+
+	if (skb->ip_summed == CHECKSUM_COMPLETE)
+		csum_replace(&skb->csum, (__force __wsum)htonl(ofl), (__force __wsum)htonl(fl));
+}
+
+static void set_ipv6_ttl(struct sk_buff *skb, struct ipv6hdr *nh, u8 new_ttl, u8 mask)
+{
+	new_ttl = OVS_MASKED(nh->hop_limit, new_ttl, mask);
+
+	if (skb->ip_summed == CHECKSUM_COMPLETE)
+		csum_replace(&skb->csum, (__force __wsum)(nh->hop_limit << 8),
+			     (__force __wsum)(new_ttl << 8));
+	nh->hop_limit = new_ttl;
 }
 
 static void set_ip_ttl(struct sk_buff *skb, struct iphdr *nh, u8 new_ttl,
@@ -546,18 +577,17 @@ static int set_ipv6(struct sk_buff *skb, struct sw_flow_key *flow_key,
 		}
 	}
 	if (mask->ipv6_tclass) {
-		ipv6_change_dsfield(nh, ~mask->ipv6_tclass, key->ipv6_tclass);
+		set_ipv6_dsfield(skb, nh, key->ipv6_tclass, mask->ipv6_tclass);
 		flow_key->ip.tos = ipv6_get_dsfield(nh);
 	}
 	if (mask->ipv6_label) {
-		set_ipv6_fl(nh, ntohl(key->ipv6_label),
+		set_ipv6_fl(skb, nh, ntohl(key->ipv6_label),
 			    ntohl(mask->ipv6_label));
 		flow_key->ipv6.label =
 		    *(__be32 *)nh & htonl(IPV6_FLOWINFO_FLOWLABEL);
 	}
 	if (mask->ipv6_hlimit) {
-		OVS_SET_MASKED(nh->hop_limit, key->ipv6_hlimit,
-			       mask->ipv6_hlimit);
+		set_ipv6_ttl(skb, nh, key->ipv6_hlimit, mask->ipv6_hlimit);
 		flow_key->ip.ttl = nh->hop_limit;
 	}
 	return 0;