From: Mohsin Kazmi <sykazmi@cisco.com>
Date: Thu, 22 May 2025 19:34:42 +0000 (+0000)
Subject: ip: compute checksums before fragmentation if offloaded
X-Git-Tag: v26.02-rc0~281
X-Git-Url: https://gerrit.fd.io/r/gitweb?a=commitdiff_plain;h=refs%2Fchanges%2F91%2F42891%2F5;p=vpp.git

ip: compute checksums before fragmentation if offloaded

Type: fix

When a packet with checksum offloading enabled is
fragmented into multiple IP fragments, due to the
egress interface's MTU being smaller than the original
packet size, it gets dropped after reassembly because
the reconstructed packet contains an invalid checksum.

This patch addresses the issue by computing the checksum
in the IP fragmentation logic before the packet is
fragmented, ensuring the resulting fragments carry a
valid checksum upon reassembly.

Signed-off-by: Mohsin Kazmi <sykazmi@cisco.com>
Change-Id: I202f169887ae9594f9580a4c7901d7b4483ef5f9
---

diff --git a/src/vnet/ip/ip_frag.c b/src/vnet/ip/ip_frag.c
index 934e40a5d18..729aa677d48 100644
--- a/src/vnet/ip/ip_frag.c
+++ b/src/vnet/ip/ip_frag.c
@@ -22,6 +22,7 @@
 #include "ip_frag.h"
 
 #include <vnet/ip/ip.h>
+#include <vnet/interface_output.h>
 
 typedef struct
 {
@@ -99,6 +100,14 @@ ip4_frag_do_fragment (vlib_main_t * vm, u32 from_bi, u16 mtu,
   u8 *org_from_packet, more;
 
   from_b = vlib_get_buffer (vm, from_bi);
+
+  if (from_b->flags & VNET_BUFFER_F_OFFLOAD)
+    {
+      ASSERT ((from_b->flags & VNET_BUFFER_F_GSO) == 0);
+      vnet_calc_checksums_inline (vm, from_b, 1 /* is_v4 */, 0 /* is_v6 */);
+      vnet_calc_outer_checksums_inline (vm, from_b);
+    }
+
   org_from_packet = vlib_buffer_get_current (from_b);
   ip4 = vlib_buffer_get_current (from_b) + l2unfragmentablesize;
 
@@ -172,15 +181,6 @@ ip4_frag_do_fragment (vlib_main_t * vm, u32 from_bi, u16 mtu,
       vlib_buffer_copy_trace_flag (vm, from_b, to_bi);
       to_b->flags |= VNET_BUFFER_F_L3_HDR_OFFSET_VALID;
 
-      if (from_b->flags & VNET_BUFFER_F_L4_HDR_OFFSET_VALID)
-	{
-	  vnet_buffer (to_b)->l4_hdr_offset =
-	    (vnet_buffer (to_b)->l3_hdr_offset +
-	     (vnet_buffer (from_b)->l4_hdr_offset -
-	      vnet_buffer (from_b)->l3_hdr_offset));
-	  to_b->flags |= VNET_BUFFER_F_L4_HDR_OFFSET_VALID;
-	}
-
       /* Spin through from buffers filling up the to buffer */
       u16 left_in_to_buffer = len, to_ptr = 0;
       while (1)
@@ -221,9 +221,6 @@ ip4_frag_do_fragment (vlib_main_t * vm, u32 from_bi, u16 mtu,
       to_ip4->length = clib_host_to_net_u16 (len + sizeof (ip4_header_t));
       to_ip4->checksum = ip4_header_checksum (to_ip4);
 
-      /* we've just done the IP checksum .. */
-      vnet_buffer_offload_flags_clear (to_b, VNET_BUFFER_OFFLOAD_F_IP_CKSUM);
-
       rem -= len;
       fo += len;
     }
@@ -385,6 +382,14 @@ ip6_frag_do_fragment (vlib_main_t * vm, u32 from_bi, u16 mtu,
   u16 head_bytes;
 
   from_b = vlib_get_buffer (vm, from_bi);
+
+  if (from_b->flags & VNET_BUFFER_F_OFFLOAD)
+    {
+      ASSERT ((from_b->flags & VNET_BUFFER_F_GSO) == 0);
+      vnet_calc_checksums_inline (vm, from_b, 0 /* is_v4 */, 1 /* is_v6 */);
+      vnet_calc_outer_checksums_inline (vm, from_b);
+    }
+
   org_from_packet = vlib_buffer_get_current (from_b);
   ip6 = vlib_buffer_get_current (from_b) + l2unfragmentablesize;
 
@@ -443,15 +448,6 @@ ip6_frag_do_fragment (vlib_main_t * vm, u32 from_bi, u16 mtu,
 
       vnet_buffer (to_b)->l3_hdr_offset = to_b->current_data;
       to_b->flags |= VNET_BUFFER_F_L3_HDR_OFFSET_VALID;
-
-      if (from_b->flags & VNET_BUFFER_F_L4_HDR_OFFSET_VALID)
-	{
-	  vnet_buffer (to_b)->l4_hdr_offset =
-	    (vnet_buffer (to_b)->l3_hdr_offset +
-	     (vnet_buffer (from_b)->l4_hdr_offset -
-	      vnet_buffer (from_b)->l3_hdr_offset));
-	  to_b->flags |= VNET_BUFFER_F_L4_HDR_OFFSET_VALID;
-	}
       to_b->flags |= VNET_BUFFER_F_IS_IP6;
 
       /* Spin through from buffers filling up the to buffer */