drivers/net, ipv6: Select IPv6 fragment idents for virtio UFO packets

UFO is now disabled on all drivers that work with virtio net headers,
but userland may try to send UFO/IPv6 packets anyway.  Instead of
sending with ID=0, we should select identifiers on their behalf (as we
used to).

Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Fixes: 916e4cf46d02 ("ipv6: reuse ip6_frag_id from ip6_ufo_append_data")
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 34 insertions, 0 deletions

diff --git a/net/ipv6/output_core.c b/net/ipv6/output_core.c
index fc24c39..97f41a3 100644
--- a/net/ipv6/output_core.c
+++ b/net/ipv6/output_core.c
@@ -3,11 +3,45 @@
  * not configured or static.  These functions are needed by GSO/GRO implementation.
  */
 #include <linux/export.h>
+#include <net/ip.h>
 #include <net/ipv6.h>
 #include <net/ip6_fib.h>
 #include <net/addrconf.h>
 #include <net/secure_seq.h>
 
+/* This function exists only for tap drivers that must support broken
+ * clients requesting UFO without specifying an IPv6 fragment ID.
+ *
+ * This is similar to ipv6_select_ident() but we use an independent hash
+ * seed to limit information leakage.
+ *
+ * The network header must be set before calling this.
+ */
+void ipv6_proxy_select_ident(struct sk_buff *skb)
+{
+	static u32 ip6_proxy_idents_hashrnd __read_mostly;
+	struct in6_addr buf[2];
+	struct in6_addr *addrs;
+	u32 hash, id;
+
+	addrs = skb_header_pointer(skb,
+				   skb_network_offset(skb) +
+				   offsetof(struct ipv6hdr, saddr),
+				   sizeof(buf), buf);
+	if (!addrs)
+		return;
+
+	net_get_random_once(&ip6_proxy_idents_hashrnd,
+			    sizeof(ip6_proxy_idents_hashrnd));
+
+	hash = __ipv6_addr_jhash(&addrs[1], ip6_proxy_idents_hashrnd);
+	hash = __ipv6_addr_jhash(&addrs[0], hash);
+
+	id = ip_idents_reserve(hash, 1);
+	skb_shinfo(skb)->ip6_frag_id = htonl(id);
+}
+EXPORT_SYMBOL_GPL(ipv6_proxy_select_ident);
+
 int ip6_find_1stfragopt(struct sk_buff *skb, u8 **nexthdr)
 {
 	u16 offset = sizeof(struct ipv6hdr);