ipv6: sr: fix TLVs not being copied using setsockopt

Function ipv6_push_rthdr4 allows to add an IPv6 Segment Routing Header
to a socket through setsockopt, but the current implementation doesn't
copy possible TLVs at the end of the SRH received from userspace.

Therefore, the execution of the following branch if (sr_has_hmac(sr_phdr))
{ ... } will never complete since the len and type fields of a possible
HMAC TLV are not copied, hence seg6_get_tlv_hmac will return an error,
and the HMAC will not be computed.

This commit adds a memcpy in case TLVs have been appended to the SRH.

Fixes: a149e7c ("ipv6: sr: add support for SRH injection through setsockopt")
Acked-by: David Lebrun <dlebrun@google.com>
Signed-off-by: Mathieu Xhonneux <m.xhonneux@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv6/exthdrs.c

@@ -925,6 +925,15 @@ static void ipv6_push_rthdr4(struct sk_buff *skb, u8 *proto,
 	sr_phdr->segments[0] = **addr_p;
 	*addr_p = &sr_ihdr->segments[sr_ihdr->segments_left];
 
+	if (sr_ihdr->hdrlen > hops * 2) {
+		int tlvs_offset, tlvs_length;
+
+		tlvs_offset = (1 + hops * 2) << 3;
+		tlvs_length = (sr_ihdr->hdrlen - hops * 2) << 3;
+		memcpy((char *)sr_phdr + tlvs_offset,
+		       (char *)sr_ihdr + tlvs_offset, tlvs_length);
+	}
+
 #ifdef CONFIG_IPV6_SEG6_HMAC
 	if (sr_has_hmac(sr_phdr)) {
 		struct net *net = NULL;