From 61c67fc2295e522c7a12175581d6928c3951c0bf Mon Sep 17 00:00:00 2001
From: Simon Goldschmidt <goldsimon@gmx.de>
Date: Thu, 30 Jan 2020 23:02:16 +0100
Subject: [PATCH] ip_forward: fix IPv4 forwarding with multiple
 netifs/offloading

When we have multiple netifs where at least one has checksum offloading
capabilities, IP forwarding needs to set various checksum fields to 0
to prevent HW algorithms on calculating an invalid checksum.

-> set checksum fields of IP/UDP/TCP/ICMP to 0 in ip4_forward().

See bug #56288

Signed-off-by: Simon Goldschmidt <goldsimon@gmx.de>
---
 src/core/ipv4/ip4.c      | 31 +++++++++++++++++++++++++++++++
 src/include/lwip/netif.h |  4 +++-
 2 files changed, 34 insertions(+), 1 deletion(-)

diff --git a/src/core/ipv4/ip4.c b/src/core/ipv4/ip4.c
index 60d4042d..19144c92 100644
--- a/src/core/ipv4/ip4.c
+++ b/src/core/ipv4/ip4.c
@@ -336,6 +336,37 @@ ip4_forward(struct pbuf *p, struct ip_hdr *iphdr, struct netif *inp)
     IPH_CHKSUM_SET(iphdr, (u16_t)(IPH_CHKSUM(iphdr) + PP_HTONS(0x100)));
   }
 
+  /* Take care of setting checksums to 0 for checksum offload netifs */
+  if (CHECKSUM_GEN_IP || NETIF_CHECKSUM_ENABLED(inp, NETIF_CHECKSUM_GEN_IP)) {
+    IPH_CHKSUM_SET(iphdr, 0);
+  }
+  switch (IPH_PROTO(iphdr)) {
+#if LWIP_UDP
+#if LWIP_UDPLITE
+  case IP_PROTO_UDPLITE:
+#endif
+  case IP_PROTO_UDP:
+    if (CHECKSUM_GEN_UDP || NETIF_CHECKSUM_ENABLED(inp, NETIF_CHECKSUM_GEN_UDP)) {
+      ((struct udp_hdr *)((const u8_t *)iphdr + IPH_HL_BYTES(iphdr)))->chksum = 0;
+    }
+    break;
+#endif
+#if LWIP_TCP
+  case IP_PROTO_TCP:
+    if (CHECKSUM_GEN_TCP || NETIF_CHECKSUM_ENABLED(inp, NETIF_CHECKSUM_GEN_TCP)) {
+      ((struct tcp_hdr *)((const u8_t *)iphdr + IPH_HL_BYTES(iphdr)))->chksum = 0;
+    }
+    break;
+#endif
+#if LWIP_ICMP
+  case IP_PROTO_ICMP:
+    if (CHECKSUM_GEN_ICMP || NETIF_CHECKSUM_ENABLED(inp, NETIF_CHECKSUM_GEN_ICMP)) {
+      ((struct icmp_hdr *)((const u8_t *)iphdr + IPH_HL_BYTES(iphdr)))->chksum = 0;
+    }
+    break;
+#endif
+  }
+
   LWIP_DEBUGF(IP_DEBUG, ("ip4_forward: forwarding packet to %"U16_F".%"U16_F".%"U16_F".%"U16_F"\n",
                          ip4_addr1_16(ip4_current_dest_addr()), ip4_addr2_16(ip4_current_dest_addr()),
                          ip4_addr3_16(ip4_current_dest_addr()), ip4_addr4_16(ip4_current_dest_addr())));
diff --git a/src/include/lwip/netif.h b/src/include/lwip/netif.h
index 1bdb14ee..900029e2 100644
--- a/src/include/lwip/netif.h
+++ b/src/include/lwip/netif.h
@@ -404,8 +404,10 @@ struct netif {
 #if LWIP_CHECKSUM_CTRL_PER_NETIF
 #define NETIF_SET_CHECKSUM_CTRL(netif, chksumflags) do { \
   (netif)->chksum_flags = chksumflags; } while(0)
-#define IF__NETIF_CHECKSUM_ENABLED(netif, chksumflag) if (((netif) == NULL) || (((netif)->chksum_flags & (chksumflag)) != 0))
+#define NETIF_CHECKSUM_ENABLED(netif, chksumflag) (((netif) == NULL) || (((netif)->chksum_flags & (chksumflag)) != 0))
+#define IF__NETIF_CHECKSUM_ENABLED(netif, chksumflag) if NETIF_CHECKSUM_ENABLED(netif, chksumflag)
 #else /* LWIP_CHECKSUM_CTRL_PER_NETIF */
+#define NETIF_CHECKSUM_ENABLED(netif, chksumflag) 0
 #define NETIF_SET_CHECKSUM_CTRL(netif, chksumflags)
 #define IF__NETIF_CHECKSUM_ENABLED(netif, chksumflag)
 #endif /* LWIP_CHECKSUM_CTRL_PER_NETIF */