ipv6: raw: Deduct extension header length in rawv6_push_pending_frames

The total cork length created by ip6_append_data includes extension
headers, so we must exclude them when comparing them against the
IPV6_CHECKSUM offset which does not include extension headers.
Reported-by: Kyle Zeng <zengyhkyle@gmail.com>
Fixes: 357b40a1 ("[IPV6]: IPV6_CHECKSUM socket option can corrupt kernel memory")
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv6/raw.c

@@ -505,6 +505,7 @@ static int rawv6_recvmsg(struct sock *sk, struct msghdr *msg, size_t len,
 static int rawv6_push_pending_frames(struct sock *sk, struct flowi6 *fl6,
 				     struct raw6_sock *rp)
 {
+	struct ipv6_txoptions *opt;
 	struct sk_buff *skb;
 	int err = 0;
 	int offset;
@@ -522,6 +523,9 @@ static int rawv6_push_pending_frames(struct sock *sk, struct flowi6 *fl6,
 
 	offset = rp->offset;
 	total_len = inet_sk(sk)->cork.base.length;
+	opt = inet6_sk(sk)->cork.opt;
+	total_len -= opt ? opt->opt_flen : 0;
+
 	if (offset >= total_len - 1) {
 		err = -EINVAL;
 		ip6_flush_pending_frames(sk);