inet: frags: fix defragmented packet's IP header for af_packet

When ip_frag_queue() computes positions, it assumes that the passed sk_buff does not contain L2 headers. However, when PACKET_FANOUT_FLAG_DEFRAG is used, IP defragmentation functions can be called on outgoing packets that contain L2 headers. Also, IPv4 checksum is not corrected after defragmentation.

---
 net/ipv4/ip_fragment.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

index a50dc6d..44c8f2a 100644
@@ -351,7 +351,7 @@ static int ip_frag_queue(struct ipq *qp, struct sk_buff *skb)
 	ihl = ip_hdrlen(skb);
 
 	/* Determine the position of this fragment. */
-	end = offset + skb->len - ihl;
+	end = offset + skb->len - skb_network_offset(skb) - ihl;
 	err = -EINVAL;
 
 	/* Is this the final fragment? */

@@ -381,7 +381,7 @@ static int ip_frag_queue(struct ipq *qp, struct sk_buff *skb)
 		goto err;
 
 	err = -ENOMEM;
-	if (!pskb_pull(skb, ihl))
+	if (!pskb_pull(skb, skb_network_offset(skb) + ihl))
 		goto err;
 
 	err = pskb_trim_rcsum(skb, end - offset);

@@ -641,6 +641,8 @@ static int ip_frag_reasm(struct ipq *qp, struct sk_buff *prev,
 		iph->frag_off = 0;
 	}
 
+	ip_send_check(ip_hdr(skb));
+
 	IP_INC_STATS_BH(net, IPSTATS_MIB_REASMOKS);
 	qp->q.fragments = NULL;
 	qp->q.fragments_tail = NULL;

2.4.3.573.g4eafbef

From: Edward Jee <[email protected]>
Date: Thu, 16 Jul 2015 01:54:41 -0700

This doesn't compile.

net/ipv4/ip_fragment.c: In function ‘ip_frag_reasm’:
net/ipv4/ip_fragment.c:644:23: error: ‘skb’ undeclared (first use in this function)

  ip_send_check(ip_hdr(skb));
                       ^

net/ipv4/ip_fragment.c:644:23: note: each undeclared identifier is reported only once for each function it appears in scripts/Makefile.build:258: recipe for target 'net/ipv4/ip_fragment.o' failed
make[1]: *** [net/ipv4/ip_fragment.o] Error 1
Makefile:1527: recipe for target 'net/ipv4/ip_fragment.o' failed
make: *** [net/ipv4/ip_fragment.o] Error 2

This was meant to be
ip_send_check(iph);

Sorry, will send a v2