ip: align reass.save_rewrite_lengthv20.05-rc0

By aligning vnet_buffer_opaque.ip.save_rewrite_length and
vnet_buffer_opaque.ip.reass.save_rewrite_length we prevent shallow
virtual reassembly code from overwrite save_rewrite_length, allowing
other features down the pipe to rely on this value.

A static assert is added to guard this alignment.

Type: fix
Fixes: f126e746fc01c75bc99329d10ce9127b26b23814

Change-Id: Ie7c7f3abc2a221bbcf2830c0f006a4368088b342
Signed-off-by: Klement Sekera <ksekera@cisco.com>

3 files changed, 13 insertions, 20 deletions

diff --git a/src/vnet/buffer.h b/src/vnet/buffer.h
index b174587efdd..52935612277 100644
--- a/src/vnet/buffer.h
+++ b/src/vnet/buffer.h
@@ -209,13 +209,13 @@ typedef struct
 	      /* shallow virtual reassembly output variables */
 	      struct
 	      {
-		u8 ip_proto;	/* protocol in ip header */
-		u8 icmp_type_or_tcp_flags;
-		u8 is_non_first_fragment;
-		u8 save_rewrite_length;
 		u16 l4_src_port;	/* tcp/udp/icmp src port */
 		u16 l4_dst_port;	/* tcp/udp/icmp dst port */
 		u32 tcp_ack_number;
+		u8 save_rewrite_length;
+		u8 ip_proto;	/* protocol in ip header */
+		u8 icmp_type_or_tcp_flags;
+		u8 is_non_first_fragment;
 		u32 tcp_seq_number;
 	      };
 	      /* full reassembly output variables */
@@ -397,6 +397,15 @@ STATIC_ASSERT (STRUCT_SIZE_OF (vnet_buffer_opaque_t, ip.save_rewrite_length)
 	       && VNET_REWRITE_TOTAL_BYTES < UINT8_MAX,
 	       "save_rewrite_length member must be able to hold the max value of rewrite length");
 
+STATIC_ASSERT (STRUCT_OFFSET_OF (vnet_buffer_opaque_t, ip.save_rewrite_length)
+	       == STRUCT_OFFSET_OF (vnet_buffer_opaque_t,
+				    ip.reass.save_rewrite_length)
+	       && STRUCT_OFFSET_OF (vnet_buffer_opaque_t,
+				    mpls.save_rewrite_length) ==
+	       STRUCT_OFFSET_OF (vnet_buffer_opaque_t,
+				 ip.reass.save_rewrite_length),
+	       "save_rewrite_length must be aligned so that reass doesn't overwrite it");
+
 /*
  * The opaque field of the vlib_buffer_t is interpreted as a
  * vnet_buffer_opaque_t. Hence it should be big enough to accommodate one.
diff --git a/src/vnet/ip/reass/ip4_sv_reass.c b/src/vnet/ip/reass/ip4_sv_reass.c
index b94e9b28cea..c50cf6d6728 100644
--- a/src/vnet/ip/reass/ip4_sv_reass.c
+++ b/src/vnet/ip/reass/ip4_sv_reass.c
@@ -466,8 +466,6 @@ ip4_sv_reass_inline (vlib_main_t * vm, vlib_node_runtime_t * node,
 		{
 		  next0 = IP4_SV_REASSEMBLY_NEXT_INPUT;
 		}
-	      vnet_buffer (b0)->ip.reass.save_rewrite_length =
-		vnet_buffer (b0)->ip.save_rewrite_length;
 	      vnet_buffer (b0)->ip.reass.is_non_first_fragment = 0;
 	      vnet_buffer (b0)->ip.reass.ip_proto = ip0->protocol;
 	      if (IP_PROTOCOL_TCP == ip0->protocol)
@@ -547,8 +545,6 @@ ip4_sv_reass_inline (vlib_main_t * vm, vlib_node_runtime_t * node,
 		{
 		  next0 = IP4_SV_REASSEMBLY_NEXT_INPUT;
 		}
-	      vnet_buffer (b0)->ip.reass.save_rewrite_length =
-		vnet_buffer (b0)->ip.save_rewrite_length;
 	      vnet_buffer (b0)->ip.reass.is_non_first_fragment =
 		! !fragment_first;
 	      vnet_buffer (b0)->ip.reass.ip_proto = reass->ip_proto;
@@ -620,9 +616,6 @@ ip4_sv_reass_inline (vlib_main_t * vm, vlib_node_runtime_t * node,
 		to_next[0] = bi0;
 		to_next += 1;
 		n_left_to_next -= 1;
-		ASSERT (vnet_buffer (b0)->ip.save_rewrite_length < (2 << 14));
-		vnet_buffer (b0)->ip.reass.save_rewrite_length =
-		  vnet_buffer (b0)->ip.save_rewrite_length;
 		vnet_buffer (b0)->ip.reass.is_non_first_fragment =
 		  ! !ip4_get_fragment_offset (vlib_buffer_get_current (b0));
 		vnet_buffer (b0)->ip.reass.ip_proto = reass->ip_proto;
diff --git a/src/vnet/ip/reass/ip6_sv_reass.c b/src/vnet/ip/reass/ip6_sv_reass.c
index 442617703a1..5f46966b19b 100644
--- a/src/vnet/ip/reass/ip6_sv_reass.c
+++ b/src/vnet/ip/reass/ip6_sv_reass.c
@@ -559,9 +559,6 @@ ip6_sv_reassembly_inline (vlib_main_t * vm,
 		  next0 = IP6_SV_REASSEMBLY_NEXT_DROP;
 		  goto packet_enqueue;
 		}
-	      ASSERT (vnet_buffer (b0)->ip.save_rewrite_length < (2 << 14));
-	      vnet_buffer (b0)->ip.reass.save_rewrite_length =
-		vnet_buffer (b0)->ip.save_rewrite_length;
 	      vnet_buffer (b0)->ip.reass.is_non_first_fragment = 0;
 	      next0 = IP6_SV_REASSEMBLY_NEXT_INPUT;
 	      if (PREDICT_FALSE (b0->flags & VLIB_BUFFER_IS_TRACED))
@@ -631,9 +628,6 @@ ip6_sv_reassembly_inline (vlib_main_t * vm,
 
 	  if (reass->is_complete)
 	    {
-	      ASSERT (vnet_buffer (b0)->ip.save_rewrite_length < (2 << 14));
-	      vnet_buffer (b0)->ip.reass.save_rewrite_length =
-		vnet_buffer (b0)->ip.save_rewrite_length;
 	      vnet_buffer (b0)->ip.reass.is_non_first_fragment =
 		! !ip6_frag_hdr_offset (frag_hdr);
 	      vnet_buffer (b0)->ip.reass.ip_proto = reass->ip_proto;
@@ -712,9 +706,6 @@ ip6_sv_reassembly_inline (vlib_main_t * vm,
 		frag_hdr =
 		  vlib_buffer_get_current (b0) +
 		  vnet_buffer (b0)->ip.reass.ip6_frag_hdr_offset;
-		ASSERT (vnet_buffer (b0)->ip.save_rewrite_length < (2 << 14));
-		vnet_buffer (b0)->ip.reass.save_rewrite_length =
-		  vnet_buffer (b0)->ip.save_rewrite_length;
 		vnet_buffer (b0)->ip.reass.is_non_first_fragment =
 		  ! !ip6_frag_hdr_offset (frag_hdr);
 		vnet_buffer (b0)->ip.reass.ip_proto = reass->ip_proto;