util: move IP stuff from util.[ch] to ip.[ch]

Introduce ip.[ch] file to encapsulate IP protocol handling functions and
structures.  Modify various files to include the new header ip.h when
it's needed.

Signed-off-by: Laurent Vivier <lvivier@redhat.com>
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
Message-ID: <20240303135114.1023026-5-lvivier@redhat.com>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

1 files changed, 72 insertions, 0 deletions

diff --git a/ip.c b/ip.c
new file mode 100644
index 0000000..2cc7f65
--- /dev/null
+++ b/ip.c
@@ -0,0 +1,72 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+/* PASST - Plug A Simple Socket Transport
+ *  for qemu/UNIX domain socket mode
+ *
+ * PASTA - Pack A Subtle Tap Abstraction
+ *  for network namespace/tap device mode
+ *
+ * ip.c - IP related functions
+ *
+ * Copyright (c) 2020-2021 Red Hat GmbH
+ * Author: Stefano Brivio <sbrivio@redhat.com>
+ */
+
+#include <stddef.h>
+#include "util.h"
+#include "ip.h"
+
+#define IPV6_NH_OPT(nh)							\
+	((nh) == 0   || (nh) == 43  || (nh) == 44  || (nh) == 50  ||	\
+	 (nh) == 51  || (nh) == 60  || (nh) == 135 || (nh) == 139 ||	\
+	 (nh) == 140 || (nh) == 253 || (nh) == 254)
+
+/**
+ * ipv6_l4hdr() - Find pointer to L4 header in IPv6 packet and extract protocol
+ * @p:		Packet pool, packet number @idx has IPv6 header at @offset
+ * @idx:	Index of packet in pool
+ * @offset:	Pre-calculated IPv6 header offset
+ * @proto:	Filled with L4 protocol number
+ * @dlen:	Data length (payload excluding header extensions), set on return
+ *
+ * Return: pointer to L4 header, NULL if not found
+ */
+char *ipv6_l4hdr(const struct pool *p, int idx, size_t offset, uint8_t *proto,
+		 size_t *dlen)
+{
+	const struct ipv6_opt_hdr *o;
+	const struct ipv6hdr *ip6h;
+	char *base;
+	int hdrlen;
+	uint8_t nh;
+
+	base = packet_get(p, idx, 0, 0, NULL);
+	ip6h = packet_get(p, idx, offset, sizeof(*ip6h), dlen);
+	if (!ip6h)
+		return NULL;
+
+	offset += sizeof(*ip6h);
+
+	nh = ip6h->nexthdr;
+	if (!IPV6_NH_OPT(nh))
+		goto found;
+
+	while ((o = packet_get_try(p, idx, offset, sizeof(*o), dlen))) {
+		nh = o->nexthdr;
+		hdrlen = (o->hdrlen + 1) * 8;
+
+		if (IPV6_NH_OPT(nh))
+			offset += hdrlen;
+		else
+			goto found;
+	}
+
+	return NULL;
+
+found:
+	if (nh == 59)
+		return NULL;
+
+	*proto = nh;
+	return base + offset;
+}