[PATCH 3.5 024/103] {pktgen, xfrm} Update IPv4 header total len and checksum after tranformation

[Luis Henriques]

3.5.7.28 -stable review patch.  If anyone has any objections, please let me know.

------------------

From: "fan.du" <fan.du@xxxxxxxxxxxxx>

commit 3868204d6b89ea373a273e760609cb08020beb1a upstream.

commit a553e4a6317b2cfc7659542c10fe43184ffe53da ("[PKTGEN]: IPSEC support")
tried to support IPsec ESP transport transformation for pktgen, but acctually
this doesn't work at all for two reasons(The orignal transformed packet has
bad IPv4 checksum value, as well as wrong auth value, reported by wireshark)

- After transpormation, IPv4 header total length needs update,
  because encrypted payload's length is NOT same as that of plain text.

- After transformation, IPv4 checksum needs re-caculate because of payload
  has been changed.

With this patch, armmed pktgen with below cofiguration, Wireshark is able to
decrypted ESP packet generated by pktgen without any IPv4 checksum error or
auth value error.

pgset "flag IPSEC"
pgset "flows 1"

Signed-off-by: Fan Du <fan.du@xxxxxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Luis Henriques <luis.henriques@xxxxxxxxxxxxx>
---
 net/core/pktgen.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/net/core/pktgen.c b/net/core/pktgen.c
index 2a42802..b3c5bac 100644
--- a/net/core/pktgen.c
+++ b/net/core/pktgen.c
@@ -2516,6 +2516,8 @@ static int process_ipsec(struct pktgen_dev *pkt_dev,
 		if (x) {
 			int ret;
 			__u8 *eth;
+			struct iphdr *iph;
+
 			nhead = x->props.header_len - skb_headroom(skb);
 			if (nhead > 0) {
 				ret = pskb_expand_head(skb, nhead, 0, GFP_ATOMIC);
@@ -2537,6 +2539,11 @@ static int process_ipsec(struct pktgen_dev *pkt_dev,
 			eth = (__u8 *) skb_push(skb, ETH_HLEN);
 			memcpy(eth, pkt_dev->hh, 12);
 			*(u16 *) &eth[12] = protocol;
+
+			/* Update IPv4 header len as well as checksum value */
+			iph = ip_hdr(skb);
+			iph->tot_len = htons(skb->len - ETH_HLEN);
+			ip_send_check(iph);
 		}
 	}
 	return 1;
-- 
1.8.3.2

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