xfrm: policy: replace session decode with flow dissector

xfrm needs to populate ipv4/v6 flow struct for route lookup.
In the past there were several bugs in this code:

1. callers that forget to reload header pointers after
   xfrm_decode_session() (it may pull headers).
2. bugs in decoding where accesses past skb->data occurred.

Meanwhile network core gained a packet dissector as well.
This switches xfrm to the flow dissector.

Changes since RFC:
Drop ipv6 mobiliy header support, AFAIU noone uses this.

Drop extraction of flowlabel, replaced code doesn't set it either.

Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://lore.kernel.org/netdev/20230908120628.26164-3-fw@strlen.de/
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>

diff --git a/net/xfrm/xfrm_policy.c b/net/xfrm/xfrm_policy.c
index da29be0b002f711897f6897a24079a6fc3235834..6aea8b2f45e02440847ea94628cd39a022bace1e 100644 (file)
--- a/net/xfrm/xfrm_policy.c
+++ b/net/xfrm/xfrm_policy.c
@@ -149,6 +149,21 @@ struct xfrm_pol_inexact_candidates {
        struct hlist_head *res[XFRM_POL_CAND_MAX];
 };
 
+struct xfrm_flow_keys {
+       struct flow_dissector_key_basic basic;
+       struct flow_dissector_key_control control;
+       union {
+               struct flow_dissector_key_ipv4_addrs ipv4;
+               struct flow_dissector_key_ipv6_addrs ipv6;
+       } addrs;
+       struct flow_dissector_key_ip ip;
+       struct flow_dissector_key_icmp icmp;
+       struct flow_dissector_key_ports ports;
+       struct flow_dissector_key_keyid gre;
+};
+
+static struct flow_dissector xfrm_session_dissector __ro_after_init;
+
 static DEFINE_SPINLOCK(xfrm_if_cb_lock);
 static struct xfrm_if_cb const __rcu *xfrm_if_cb __read_mostly;
 
@@ -3367,191 +3382,74 @@ xfrm_policy_ok(const struct xfrm_tmpl *tmpl, const struct sec_path *sp, int star
 }
 
 static void
-decode_session4(struct sk_buff *skb, struct flowi *fl, bool reverse)
+decode_session4(const struct xfrm_flow_keys *flkeys, struct flowi *fl, bool reverse)
 {
-       const struct iphdr *iph = ip_hdr(skb);
-       int ihl = iph->ihl;
-       u8 *xprth = skb_network_header(skb) + ihl * 4;
        struct flowi4 *fl4 = &fl->u.ip4;
 
        memset(fl4, 0, sizeof(struct flowi4));
 
-       fl4->flowi4_proto = iph->protocol;
-       fl4->daddr = reverse ? iph->saddr : iph->daddr;
-       fl4->saddr = reverse ? iph->daddr : iph->saddr;
-       fl4->flowi4_tos = iph->tos & ~INET_ECN_MASK;
-
-       if (!ip_is_fragment(iph)) {
-               switch (iph->protocol) {
-               case IPPROTO_UDP:
-               case IPPROTO_UDPLITE:
-               case IPPROTO_TCP:
-               case IPPROTO_SCTP:
-               case IPPROTO_DCCP:
-                       if (xprth + 4 < skb->data ||
-                           pskb_may_pull(skb, xprth + 4 - skb->data)) {
-                               __be16 *ports;
-
-                               xprth = skb_network_header(skb) + ihl * 4;
-                               ports = (__be16 *)xprth;
-
-                               fl4->fl4_sport = ports[!!reverse];
-                               fl4->fl4_dport = ports[!reverse];
-                       }
-                       break;
-               case IPPROTO_ICMP:
-                       if (xprth + 2 < skb->data ||
-                           pskb_may_pull(skb, xprth + 2 - skb->data)) {
-                               u8 *icmp;
-
-                               xprth = skb_network_header(skb) + ihl * 4;
-                               icmp = xprth;
-
-                               fl4->fl4_icmp_type = icmp[0];
-                               fl4->fl4_icmp_code = icmp[1];
-                       }
-                       break;
-               case IPPROTO_GRE:
-                       if (xprth + 12 < skb->data ||
-                           pskb_may_pull(skb, xprth + 12 - skb->data)) {
-                               __be16 *greflags;
-                               __be32 *gre_hdr;
-
-                               xprth = skb_network_header(skb) + ihl * 4;
-                               greflags = (__be16 *)xprth;
-                               gre_hdr = (__be32 *)xprth;
-
-                               if (greflags[0] & GRE_KEY) {
-                                       if (greflags[0] & GRE_CSUM)
-                                               gre_hdr++;
-                                       fl4->fl4_gre_key = gre_hdr[1];
-                               }
-                       }
-                       break;
-               default:
-                       break;
-               }
+       if (reverse) {
+               fl4->saddr = flkeys->addrs.ipv4.dst;
+               fl4->daddr = flkeys->addrs.ipv4.src;
+               fl4->fl4_sport = flkeys->ports.dst;
+               fl4->fl4_dport = flkeys->ports.src;
+       } else {
+               fl4->saddr = flkeys->addrs.ipv4.src;
+               fl4->daddr = flkeys->addrs.ipv4.dst;
+               fl4->fl4_sport = flkeys->ports.src;
+               fl4->fl4_dport = flkeys->ports.dst;
        }
+
+       fl4->flowi4_proto = flkeys->basic.ip_proto;
+       fl4->flowi4_tos = flkeys->ip.tos;
+       fl4->fl4_icmp_type = flkeys->icmp.type;
+       fl4->fl4_icmp_type = flkeys->icmp.code;
+       fl4->fl4_gre_key = flkeys->gre.keyid;
 }
 
 #if IS_ENABLED(CONFIG_IPV6)
 static void
-decode_session6(struct sk_buff *skb, struct flowi *fl, bool reverse)
+decode_session6(const struct xfrm_flow_keys *flkeys, struct flowi *fl, bool reverse)
 {
        struct flowi6 *fl6 = &fl->u.ip6;
-       int onlyproto = 0;
-       const struct ipv6hdr *hdr = ipv6_hdr(skb);
-       u32 offset = sizeof(*hdr);
-       struct ipv6_opt_hdr *exthdr;
-       const unsigned char *nh = skb_network_header(skb);
-       u16 nhoff = IP6CB(skb)->nhoff;
-       u8 nexthdr;
-
-       if (!nhoff)
-               nhoff = offsetof(struct ipv6hdr, nexthdr);
-
-       nexthdr = nh[nhoff];
 
        memset(fl6, 0, sizeof(struct flowi6));
 
-       fl6->daddr = reverse ? hdr->saddr : hdr->daddr;
-       fl6->saddr = reverse ? hdr->daddr : hdr->saddr;
-
-       while (nh + offset + sizeof(*exthdr) < skb->data ||
-              pskb_may_pull(skb, nh + offset + sizeof(*exthdr) - skb->data)) {
-               nh = skb_network_header(skb);
-               exthdr = (struct ipv6_opt_hdr *)(nh + offset);
-
-               switch (nexthdr) {
-               case NEXTHDR_FRAGMENT:
-                       onlyproto = 1;
-                       fallthrough;
-               case NEXTHDR_ROUTING:
-               case NEXTHDR_HOP:
-               case NEXTHDR_DEST:
-                       offset += ipv6_optlen(exthdr);
-                       nexthdr = exthdr->nexthdr;
-                       break;
-               case IPPROTO_UDP:
-               case IPPROTO_UDPLITE:
-               case IPPROTO_TCP:
-               case IPPROTO_SCTP:
-               case IPPROTO_DCCP:
-                       if (!onlyproto && (nh + offset + 4 < skb->data ||
-                            pskb_may_pull(skb, nh + offset + 4 - skb->data))) {
-                               __be16 *ports;
-
-                               nh = skb_network_header(skb);
-                               ports = (__be16 *)(nh + offset);
-                               fl6->fl6_sport = ports[!!reverse];
-                               fl6->fl6_dport = ports[!reverse];
-                       }
-                       fl6->flowi6_proto = nexthdr;
-                       return;
-               case IPPROTO_ICMPV6:
-                       if (!onlyproto && (nh + offset + 2 < skb->data ||
-                           pskb_may_pull(skb, nh + offset + 2 - skb->data))) {
-                               u8 *icmp;
-
-                               nh = skb_network_header(skb);
-                               icmp = (u8 *)(nh + offset);
-                               fl6->fl6_icmp_type = icmp[0];
-                               fl6->fl6_icmp_code = icmp[1];
-                       }
-                       fl6->flowi6_proto = nexthdr;
-                       return;
-               case IPPROTO_GRE:
-                       if (!onlyproto &&
-                           (nh + offset + 12 < skb->data ||
-                            pskb_may_pull(skb, nh + offset + 12 - skb->data))) {
-                               struct gre_base_hdr *gre_hdr;
-                               __be32 *gre_key;
-
-                               nh = skb_network_header(skb);
-                               gre_hdr = (struct gre_base_hdr *)(nh + offset);
-                               gre_key = (__be32 *)(gre_hdr + 1);
-
-                               if (gre_hdr->flags & GRE_KEY) {
-                                       if (gre_hdr->flags & GRE_CSUM)
-                                               gre_key++;
-                                       fl6->fl6_gre_key = *gre_key;
-                               }
-                       }
-                       fl6->flowi6_proto = nexthdr;
-                       return;
-
-#if IS_ENABLED(CONFIG_IPV6_MIP6)
-               case IPPROTO_MH:
-                       offset += ipv6_optlen(exthdr);
-                       if (!onlyproto && (nh + offset + 3 < skb->data ||
-                           pskb_may_pull(skb, nh + offset + 3 - skb->data))) {
-                               struct ip6_mh *mh;
-
-                               nh = skb_network_header(skb);
-                               mh = (struct ip6_mh *)(nh + offset);
-                               fl6->fl6_mh_type = mh->ip6mh_type;
-                       }
-                       fl6->flowi6_proto = nexthdr;
-                       return;
-#endif
-               default:
-                       fl6->flowi6_proto = nexthdr;
-                       return;
-               }
+       if (reverse) {
+               fl6->saddr = flkeys->addrs.ipv6.dst;
+               fl6->daddr = flkeys->addrs.ipv6.src;
+               fl6->fl6_sport = flkeys->ports.dst;
+               fl6->fl6_dport = flkeys->ports.src;
+       } else {
+               fl6->saddr = flkeys->addrs.ipv6.src;
+               fl6->daddr = flkeys->addrs.ipv6.dst;
+               fl6->fl6_sport = flkeys->ports.src;
+               fl6->fl6_dport = flkeys->ports.dst;
        }
+
+       fl6->flowi6_proto = flkeys->basic.ip_proto;
+       fl6->fl6_icmp_type = flkeys->icmp.type;
+       fl6->fl6_icmp_type = flkeys->icmp.code;
+       fl6->fl6_gre_key = flkeys->gre.keyid;
 }
 #endif
 
 int __xfrm_decode_session(struct net *net, struct sk_buff *skb, struct flowi *fl,
                          unsigned int family, int reverse)
 {
+       struct xfrm_flow_keys flkeys;
+
+       memset(&flkeys, 0, sizeof(flkeys));
+       __skb_flow_dissect(net, skb, &xfrm_session_dissector, &flkeys,
+                          NULL, 0, 0, 0, FLOW_DISSECTOR_F_STOP_AT_ENCAP);
+
        switch (family) {
        case AF_INET:
-               decode_session4(skb, fl, reverse);
+               decode_session4(&flkeys, fl, reverse);
                break;
 #if IS_ENABLED(CONFIG_IPV6)
        case AF_INET6:
-               decode_session6(skb, fl, reverse);
+               decode_session6(&flkeys, fl, reverse);
                break;
 #endif
        default:
@@ -4253,8 +4151,47 @@ static struct pernet_operations __net_initdata xfrm_net_ops = {
        .exit = xfrm_net_exit,
 };
 
+static const struct flow_dissector_key xfrm_flow_dissector_keys[] = {
+       {
+               .key_id = FLOW_DISSECTOR_KEY_CONTROL,
+               .offset = offsetof(struct xfrm_flow_keys, control),
+       },
+       {
+               .key_id = FLOW_DISSECTOR_KEY_BASIC,
+               .offset = offsetof(struct xfrm_flow_keys, basic),
+       },
+       {
+               .key_id = FLOW_DISSECTOR_KEY_IPV4_ADDRS,
+               .offset = offsetof(struct xfrm_flow_keys, addrs.ipv4),
+       },
+       {
+               .key_id = FLOW_DISSECTOR_KEY_IPV6_ADDRS,
+               .offset = offsetof(struct xfrm_flow_keys, addrs.ipv6),
+       },
+       {
+               .key_id = FLOW_DISSECTOR_KEY_PORTS,
+               .offset = offsetof(struct xfrm_flow_keys, ports),
+       },
+       {
+               .key_id = FLOW_DISSECTOR_KEY_GRE_KEYID,
+               .offset = offsetof(struct xfrm_flow_keys, gre),
+       },
+       {
+               .key_id = FLOW_DISSECTOR_KEY_IP,
+               .offset = offsetof(struct xfrm_flow_keys, ip),
+       },
+       {
+               .key_id = FLOW_DISSECTOR_KEY_ICMP,
+               .offset = offsetof(struct xfrm_flow_keys, icmp),
+       },
+};
+
 void __init xfrm_init(void)
 {
+       skb_flow_dissector_init(&xfrm_session_dissector,
+                               xfrm_flow_dissector_keys,
+                               ARRAY_SIZE(xfrm_flow_dissector_keys));
+
        register_pernet_subsys(&xfrm_net_ops);
        xfrm_dev_init();
        xfrm_input_init();