netfilter: x_tables: don't extract flow keys on early demuxed sks in socket match

Currently in xt_socket, we take advantage of early demuxed sockets
since commit 00028aa37098 ("netfilter: xt_socket: use IP early demux")
in order to avoid a second socket lookup in the fast path, but we
only make partial use of this:

We still unnecessarily parse headers, extract proto, {s,d}addr and
{s,d}ports from the skb data, accessing possible conntrack information,
etc even though we were not even calling into the socket lookup via
xt_socket_get_sock_{v4,v6}() due to skb->sk hit, meaning those cycles
can be spared.

After this patch, we only proceed the slower, manual lookup path
when we have a skb->sk miss, thus time to match verdict for early
demuxed sockets will improve further, which might be i.e. interesting
for use cases such as mentioned in 681f130f39e1 ("netfilter: xt_socket:
add XT_SOCKET_NOWILDCARD flag").

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

1 files changed, 50 insertions, 45 deletions

diff --git a/net/netfilter/xt_socket.c b/net/netfilter/xt_socket.c
index 895534e87a47..e092cb046326 100644
--- a/net/netfilter/xt_socket.c
+++ b/net/netfilter/xt_socket.c
@@ -143,13 +143,10 @@ static bool xt_socket_sk_is_transparent(struct sock *sk)
         }
 }
 
-static bool
-socket_match(const struct sk_buff *skb, struct xt_action_param *par,
-             const struct xt_socket_mtinfo1 *info)
+static struct sock *xt_socket_lookup_slow_v4(const struct sk_buff *skb,
+                                             const struct net_device *indev)
 {
         const struct iphdr *iph = ip_hdr(skb);
-        struct udphdr _hdr, *hp = NULL;
-        struct sock *sk = skb->sk;
         __be32 uninitialized_var(daddr), uninitialized_var(saddr);
         __be16 uninitialized_var(dport), uninitialized_var(sport);
         u8 uninitialized_var(protocol);
@@ -159,10 +156,12 @@ socket_match(const struct sk_buff *skb, struct xt_action_param *par,
 #endif
 
         if (iph->protocol == IPPROTO_UDP || iph->protocol == IPPROTO_TCP) {
+                struct udphdr _hdr, *hp;
+
                 hp = skb_header_pointer(skb, ip_hdrlen(skb),
                                         sizeof(_hdr), &_hdr);
                 if (hp == NULL)
-                        return false;
+                        return NULL;
 
                 protocol = iph->protocol;
                 saddr = iph->saddr;
@@ -172,16 +171,17 @@ socket_match(const struct sk_buff *skb, struct xt_action_param *par,
 
         } else if (iph->protocol == IPPROTO_ICMP) {
                 if (extract_icmp4_fields(skb, &protocol, &saddr, &daddr,
-                                        &sport, &dport))
-                        return false;
+                                         &sport, &dport))
+                        return NULL;
         } else {
-                return false;
+                return NULL;
         }
 
 #ifdef XT_SOCKET_HAVE_CONNTRACK
-        /* Do the lookup with the original socket address in case this is a
-         * reply packet of an established SNAT-ted connection. */
-
+        /* Do the lookup with the original socket address in
+         * case this is a reply packet of an established
+         * SNAT-ted connection.
+         */
         ct = nf_ct_get(skb, &ctinfo);
         if (ct && !nf_ct_is_untracked(ct) &&
             ((iph->protocol != IPPROTO_ICMP &&
@@ -197,10 +197,18 @@ socket_match(const struct sk_buff *skb, struct xt_action_param *par,
         }
 #endif
 
+        return xt_socket_get_sock_v4(dev_net(skb->dev), protocol, saddr, daddr,
+                                     sport, dport, indev);
+}
+
+static bool
+socket_match(const struct sk_buff *skb, struct xt_action_param *par,
+             const struct xt_socket_mtinfo1 *info)
+{
+        struct sock *sk = skb->sk;
+
         if (!sk)
-                sk = xt_socket_get_sock_v4(dev_net(skb->dev), protocol,
-                                           saddr, daddr, sport, dport,
-                                           par->in);
+                sk = xt_socket_lookup_slow_v4(skb, par->in);
         if (sk) {
                 bool wildcard;
                 bool transparent = true;
@@ -225,12 +233,7 @@ socket_match(const struct sk_buff *skb, struct xt_action_param *par,
                         sk = NULL;
         }
 
-        pr_debug("proto %hhu %pI4:%hu -> %pI4:%hu (orig %pI4:%hu) sock %p\n",
-                 protocol, &saddr, ntohs(sport),
-                 &daddr, ntohs(dport),
-                 &iph->daddr, hp ? ntohs(hp->dest) : 0, sk);
-
-        return (sk != NULL);
+        return sk != NULL;
 }
 
 static bool
@@ -327,28 +330,26 @@ xt_socket_get_sock_v6(struct net *net, const u8 protocol,
         return NULL;
 }
 
-static bool
-socket_mt6_v1_v2(const struct sk_buff *skb, struct xt_action_param *par)
+static struct sock *xt_socket_lookup_slow_v6(const struct sk_buff *skb,
+                                             const struct net_device *indev)
 {
-        struct ipv6hdr ipv6_var, *iph = ipv6_hdr(skb);
-        struct udphdr _hdr, *hp = NULL;
-        struct sock *sk = skb->sk;
-        const struct in6_addr *daddr = NULL, *saddr = NULL;
         __be16 uninitialized_var(dport), uninitialized_var(sport);
-        int thoff = 0, uninitialized_var(tproto);
-        const struct xt_socket_mtinfo1 *info = (struct xt_socket_mtinfo1 *) par->matchinfo;
+        const struct in6_addr *daddr = NULL, *saddr = NULL;
+        struct ipv6hdr *iph = ipv6_hdr(skb);
+        int thoff = 0, tproto;
 
         tproto = ipv6_find_hdr(skb, &thoff, -1, NULL, NULL);
         if (tproto < 0) {
                 pr_debug("unable to find transport header in IPv6 packet, dropping\n");
-                return NF_DROP;
+                return NULL;
         }
 
         if (tproto == IPPROTO_UDP || tproto == IPPROTO_TCP) {
-                hp = skb_header_pointer(skb, thoff,
-                                        sizeof(_hdr), &_hdr);
+                struct udphdr _hdr, *hp;
+
+                hp = skb_header_pointer(skb, thoff, sizeof(_hdr), &_hdr);
                 if (hp == NULL)
-                        return false;
+                        return NULL;
 
                 saddr = &iph->saddr;
                 sport = hp->source;
@@ -356,17 +357,27 @@ socket_mt6_v1_v2(const struct sk_buff *skb, struct xt_action_param *par)
                 dport = hp->dest;
 
         } else if (tproto == IPPROTO_ICMPV6) {
+                struct ipv6hdr ipv6_var;
+
                 if (extract_icmp6_fields(skb, thoff, &tproto, &saddr, &daddr,
                                          &sport, &dport, &ipv6_var))
-                        return false;
+                        return NULL;
         } else {
-                return false;
+                return NULL;
         }
 
+        return xt_socket_get_sock_v6(dev_net(skb->dev), tproto, saddr, daddr,
+                                     sport, dport, indev);
+}
+
+static bool
+socket_mt6_v1_v2(const struct sk_buff *skb, struct xt_action_param *par)
+{
+        const struct xt_socket_mtinfo1 *info = (struct xt_socket_mtinfo1 *) par->matchinfo;
+        struct sock *sk = skb->sk;
+
         if (!sk)
-                sk = xt_socket_get_sock_v6(dev_net(skb->dev), tproto,
-                                           saddr, daddr, sport, dport,
-                                           par->in);
+                sk = xt_socket_lookup_slow_v6(skb, par->in);
         if (sk) {
                 bool wildcard;
                 bool transparent = true;
@@ -391,13 +402,7 @@ socket_mt6_v1_v2(const struct sk_buff *skb, struct xt_action_param *par)
                         sk = NULL;
         }
 
-        pr_debug("proto %hhd %pI6:%hu -> %pI6:%hu "
-                 "(orig %pI6:%hu) sock %p\n",
-                 tproto, saddr, ntohs(sport),
-                 daddr, ntohs(dport),
-                 &iph->daddr, hp ? ntohs(hp->dest) : 0, sk);
-
-        return (sk != NULL);
+        return sk != NULL;
 }
 #endif