net: Add framework to allow sending packets with customized CRC.

This is useful for testing RX handling of frames with bad
CRCs.

Requires driver support to actually put the packet on the
wire properly.

Signed-off-by: Ben Greear <greearb@candelatech.com>
Tested-by: Aaron Brown <aaron.f.brown@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>

3 files changed, 34 insertions, 4 deletions

diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index f3a5307..6eb656a 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -592,6 +592,7 @@ static void __copy_skb_header(struct sk_buff *new, const struct sk_buff *old)
 	new->rxhash		= old->rxhash;
 	new->ooo_okay		= old->ooo_okay;
 	new->l4_rxhash		= old->l4_rxhash;
+	new->no_fcs		= old->no_fcs;
 #ifdef CONFIG_XFRM
 	new->sp			= secpath_get(old->sp);
 #endif
diff --git a/net/core/sock.c b/net/core/sock.c
index 19942d4..55011cb 100644
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -799,6 +799,11 @@ set_rcvbuf:
 		else
 			ret = -EOPNOTSUPP;
 		break;
+
+	case SO_NOFCS:
+		sock_valbool_flag(sk, SOCK_NOFCS, valbool);
+		break;
+
 	default:
 		ret = -ENOPROTOOPT;
 		break;
diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
index 2dbb32b..ae2d484 100644
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -1459,6 +1459,7 @@ static int packet_sendmsg_spkt(struct kiocb *iocb, struct socket *sock,
 	struct net_device *dev;
 	__be16 proto = 0;
 	int err;
+	int extra_len = 0;
 
 	/*
 	 *	Get and verify the address.
@@ -1493,8 +1494,16 @@ retry:
 	 * raw protocol and you must do your own fragmentation at this level.
 	 */
 
+	if (unlikely(sock_flag(sk, SOCK_NOFCS))) {
+		if (!netif_supports_nofcs(dev)) {
+			err = -EPROTONOSUPPORT;
+			goto out_unlock;
+		}
+		extra_len = 4; /* We're doing our own CRC */
+	}
+
 	err = -EMSGSIZE;
-	if (len > dev->mtu + dev->hard_header_len + VLAN_HLEN)
+	if (len > dev->mtu + dev->hard_header_len + VLAN_HLEN + extra_len)
 		goto out_unlock;
 
 	if (!skb) {
@@ -1526,7 +1535,7 @@ retry:
 		goto retry;
 	}
 
-	if (len > (dev->mtu + dev->hard_header_len)) {
+	if (len > (dev->mtu + dev->hard_header_len + extra_len)) {
 		/* Earlier code assumed this would be a VLAN pkt,
 		 * double-check this now that we have the actual
 		 * packet in hand.
@@ -1548,6 +1557,9 @@ retry:
 	if (err < 0)
 		goto out_unlock;
 
+	if (unlikely(extra_len == 4))
+		skb->no_fcs = 1;
+
 	dev_queue_xmit(skb);
 	rcu_read_unlock();
 	return len;
@@ -2209,6 +2221,7 @@ static int packet_snd(struct socket *sock,
 	struct packet_sock *po = pkt_sk(sk);
 	unsigned short gso_type = 0;
 	int hlen, tlen;
+	int extra_len = 0;
 
 	/*
 	 *	Get and verify the address.
@@ -2288,8 +2301,16 @@ static int packet_snd(struct socket *sock,
 		}
 	}
 
+	if (unlikely(sock_flag(sk, SOCK_NOFCS))) {
+		if (!netif_supports_nofcs(dev)) {
+			err = -EPROTONOSUPPORT;
+			goto out_unlock;
+		}
+		extra_len = 4; /* We're doing our own CRC */
+	}
+
 	err = -EMSGSIZE;
-	if (!gso_type && (len > dev->mtu + reserve + VLAN_HLEN))
+	if (!gso_type && (len > dev->mtu + reserve + VLAN_HLEN + extra_len))
 		goto out_unlock;
 
 	err = -ENOBUFS;
@@ -2315,7 +2336,7 @@ static int packet_snd(struct socket *sock,
 	if (err < 0)
 		goto out_free;
 
-	if (!gso_type && (len > dev->mtu + reserve)) {
+	if (!gso_type && (len > dev->mtu + reserve + extra_len)) {
 		/* Earlier code assumed this would be a VLAN pkt,
 		 * double-check this now that we have the actual
 		 * packet in hand.
@@ -2353,6 +2374,9 @@ static int packet_snd(struct socket *sock,
 		len += vnet_hdr_len;
 	}
 
+	if (unlikely(extra_len == 4))
+		skb->no_fcs = 1;
+
 	/*
 	 *	Now send it
 	 */