1 files changed, 46 insertions, 0 deletions

diff --git a/net/socket.c b/net/socket.c
index 985ef06792d6..c2564eb25c6b 100644
--- a/net/socket.c
+++ b/net/socket.c
@@ -3356,3 +3356,49 @@ int kernel_sock_shutdown(struct socket *sock, enum sock_shutdown_cmd how)
         return sock->ops->shutdown(sock, how);
 }
 EXPORT_SYMBOL(kernel_sock_shutdown);
+
+/* This routine returns the IP overhead imposed by a socket i.e.
+ * the length of the underlying IP header, depending on whether
+ * this is an IPv4 or IPv6 socket and the length from IP options turned
+ * on at the socket. Assumes that the caller has a lock on the socket.
+ */
+u32 kernel_sock_ip_overhead(struct sock *sk)
+{
+        struct inet_sock *inet;
+        struct ip_options_rcu *opt;
+        u32 overhead = 0;
+        bool owned_by_user;
+#if IS_ENABLED(CONFIG_IPV6)
+        struct ipv6_pinfo *np;
+        struct ipv6_txoptions *optv6 = NULL;
+#endif /* IS_ENABLED(CONFIG_IPV6) */
+
+        if (!sk)
+                return overhead;
+
+        owned_by_user = sock_owned_by_user(sk);
+        switch (sk->sk_family) {
+        case AF_INET:
+                inet = inet_sk(sk);
+                overhead += sizeof(struct iphdr);
+                opt = rcu_dereference_protected(inet->inet_opt,
+                                                owned_by_user);
+                if (opt)
+                        overhead += opt->opt.optlen;
+                return overhead;
+#if IS_ENABLED(CONFIG_IPV6)
+        case AF_INET6:
+                np = inet6_sk(sk);
+                overhead += sizeof(struct ipv6hdr);
+                if (np)
+                        optv6 = rcu_dereference_protected(np->opt,
+                                                          owned_by_user);
+                if (optv6)
+                        overhead += (optv6->opt_flen + optv6->opt_nflen);
+                return overhead;
+#endif /* IS_ENABLED(CONFIG_IPV6) */
+        default: /* Returns 0 overhead if the socket is not ipv4 or ipv6 */
+                return overhead;
+        }
+}
+EXPORT_SYMBOL(kernel_sock_ip_overhead);