bpf: Add ingress_ifindex to bpf_sk_lookup

It may be helpful to have access to the ifindex during bpf socket
lookup. An example may be to scope certain socket lookup logic to
specific interfaces, i.e. an interface may be made exempt from custom
lookup code.

Add the ifindex of the arriving connection to the bpf_sk_lookup API.
Signed-off-by: Mark Pashmfouroush <markpash@cloudflare.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20211110111016.5670-2-markpash@cloudflare.com

include/linux/filter.h

@@ -1374,6 +1374,7 @@ struct bpf_sk_lookup_kern {
 		const struct in6_addr *daddr;
 	} v6;
 	struct sock	*selected_sk;
+	u32		ingress_ifindex;
 	bool		no_reuseport;
 };
 
@@ -1436,7 +1437,7 @@ extern struct static_key_false bpf_sk_lookup_enabled;
 static inline bool bpf_sk_lookup_run_v4(struct net *net, int protocol,
 					const __be32 saddr, const __be16 sport,
 					const __be32 daddr, const u16 dport,
-					struct sock **psk)
+					const int ifindex, struct sock **psk)
 {
 	struct bpf_prog_array *run_array;
 	struct sock *selected_sk = NULL;
@@ -1452,6 +1453,7 @@ static inline bool bpf_sk_lookup_run_v4(struct net *net, int protocol,
 			.v4.daddr	= daddr,
 			.sport		= sport,
 			.dport		= dport,
+			.ingress_ifindex	= ifindex,
 		};
 		u32 act;
 
@@ -1474,7 +1476,7 @@ static inline bool bpf_sk_lookup_run_v6(struct net *net, int protocol,
 					const __be16 sport,
 					const struct in6_addr *daddr,
 					const u16 dport,
-					struct sock **psk)
+					const int ifindex, struct sock **psk)
 {
 	struct bpf_prog_array *run_array;
 	struct sock *selected_sk = NULL;
@@ -1490,6 +1492,7 @@ static inline bool bpf_sk_lookup_run_v6(struct net *net, int protocol,
 			.v6.daddr	= daddr,
 			.sport		= sport,
 			.dport		= dport,
+			.ingress_ifindex	= ifindex,
 		};
 		u32 act;
 

include/uapi/linux/bpf.h

@@ -6316,6 +6316,7 @@ struct bpf_sk_lookup {
 	__u32 local_ip4;	/* Network byte order */
 	__u32 local_ip6[4];	/* Network byte order */
 	__u32 local_port;	/* Host byte order */
+	__u32 ingress_ifindex;		/* The arriving interface. Determined by inet_iif. */
 };
 
 /*

net/core/filter.c

@@ -10491,6 +10491,7 @@ static bool sk_lookup_is_valid_access(int off, int size,
 	case bpf_ctx_range_till(struct bpf_sk_lookup, local_ip6[0], local_ip6[3]):
 	case bpf_ctx_range(struct bpf_sk_lookup, remote_port):
 	case bpf_ctx_range(struct bpf_sk_lookup, local_port):
+	case bpf_ctx_range(struct bpf_sk_lookup, ingress_ifindex):
 		bpf_ctx_record_field_size(info, sizeof(__u32));
 		return bpf_ctx_narrow_access_ok(off, size, sizeof(__u32));
 
@@ -10580,6 +10581,12 @@ static u32 sk_lookup_convert_ctx_access(enum bpf_access_type type,
 				      bpf_target_off(struct bpf_sk_lookup_kern,
 						     dport, 2, target_size));
 		break;
+
+	case offsetof(struct bpf_sk_lookup, ingress_ifindex):
+		*insn++ = BPF_LDX_MEM(BPF_W, si->dst_reg, si->src_reg,
+				      bpf_target_off(struct bpf_sk_lookup_kern,
+						     ingress_ifindex, 4, target_size));
+		break;
 	}
 
 	return insn - insn_buf;

net/ipv4/inet_hashtables.c

@@ -307,7 +307,7 @@ static inline struct sock *inet_lookup_run_bpf(struct net *net,
 					       struct inet_hashinfo *hashinfo,
 					       struct sk_buff *skb, int doff,
 					       __be32 saddr, __be16 sport,
-					       __be32 daddr, u16 hnum)
+					       __be32 daddr, u16 hnum, const int dif)
 {
 	struct sock *sk, *reuse_sk;
 	bool no_reuseport;
@@ -315,8 +315,8 @@ static inline struct sock *inet_lookup_run_bpf(struct net *net,
 	if (hashinfo != &tcp_hashinfo)
 		return NULL; /* only TCP is supported */
 
-	no_reuseport = bpf_sk_lookup_run_v4(net, IPPROTO_TCP,
-					    saddr, sport, daddr, hnum, &sk);
+	no_reuseport = bpf_sk_lookup_run_v4(net, IPPROTO_TCP, saddr, sport,
+					    daddr, hnum, dif, &sk);
 	if (no_reuseport || IS_ERR_OR_NULL(sk))
 		return sk;
 
@@ -340,7 +340,7 @@ struct sock *__inet_lookup_listener(struct net *net,
 	/* Lookup redirect from BPF */
 	if (static_branch_unlikely(&bpf_sk_lookup_enabled)) {
 		result = inet_lookup_run_bpf(net, hashinfo, skb, doff,
-					     saddr, sport, daddr, hnum);
+					     saddr, sport, daddr, hnum, dif);
 		if (result)
 			goto done;
 	}

net/ipv4/udp.c

@@ -460,7 +460,7 @@ static struct sock *udp4_lookup_run_bpf(struct net *net,
 					struct udp_table *udptable,
 					struct sk_buff *skb,
 					__be32 saddr, __be16 sport,
-					__be32 daddr, u16 hnum)
+					__be32 daddr, u16 hnum, const int dif)
 {
 	struct sock *sk, *reuse_sk;
 	bool no_reuseport;
@@ -468,8 +468,8 @@ static struct sock *udp4_lookup_run_bpf(struct net *net,
 	if (udptable != &udp_table)
 		return NULL; /* only UDP is supported */
 
-	no_reuseport = bpf_sk_lookup_run_v4(net, IPPROTO_UDP,
-					    saddr, sport, daddr, hnum, &sk);
+	no_reuseport = bpf_sk_lookup_run_v4(net, IPPROTO_UDP, saddr, sport,
+					    daddr, hnum, dif, &sk);
 	if (no_reuseport || IS_ERR_OR_NULL(sk))
 		return sk;
 
@@ -505,7 +505,7 @@ struct sock *__udp4_lib_lookup(struct net *net, __be32 saddr,
 	/* Lookup redirect from BPF */
 	if (static_branch_unlikely(&bpf_sk_lookup_enabled)) {
 		sk = udp4_lookup_run_bpf(net, udptable, skb,
-					 saddr, sport, daddr, hnum);
+					 saddr, sport, daddr, hnum, dif);
 		if (sk) {
 			result = sk;
 			goto done;

net/ipv6/inet6_hashtables.c

@@ -165,7 +165,7 @@ static inline struct sock *inet6_lookup_run_bpf(struct net *net,
 						const struct in6_addr *saddr,
 						const __be16 sport,
 						const struct in6_addr *daddr,
-						const u16 hnum)
+						const u16 hnum, const int dif)
 {
 	struct sock *sk, *reuse_sk;
 	bool no_reuseport;
@@ -173,8 +173,8 @@ static inline struct sock *inet6_lookup_run_bpf(struct net *net,
 	if (hashinfo != &tcp_hashinfo)
 		return NULL; /* only TCP is supported */
 
-	no_reuseport = bpf_sk_lookup_run_v6(net, IPPROTO_TCP,
-					    saddr, sport, daddr, hnum, &sk);
+	no_reuseport = bpf_sk_lookup_run_v6(net, IPPROTO_TCP, saddr, sport,
+					    daddr, hnum, dif, &sk);
 	if (no_reuseport || IS_ERR_OR_NULL(sk))
 		return sk;
 
@@ -198,7 +198,7 @@ struct sock *inet6_lookup_listener(struct net *net,
 	/* Lookup redirect from BPF */
 	if (static_branch_unlikely(&bpf_sk_lookup_enabled)) {
 		result = inet6_lookup_run_bpf(net, hashinfo, skb, doff,
-					      saddr, sport, daddr, hnum);
+					      saddr, sport, daddr, hnum, dif);
 		if (result)
 			goto done;
 	}

net/ipv6/udp.c

@@ -195,7 +195,7 @@ static inline struct sock *udp6_lookup_run_bpf(struct net *net,
 					       const struct in6_addr *saddr,
 					       __be16 sport,
 					       const struct in6_addr *daddr,
-					       u16 hnum)
+					       u16 hnum, const int dif)
 {
 	struct sock *sk, *reuse_sk;
 	bool no_reuseport;
@@ -203,8 +203,8 @@ static inline struct sock *udp6_lookup_run_bpf(struct net *net,
 	if (udptable != &udp_table)
 		return NULL; /* only UDP is supported */
 
-	no_reuseport = bpf_sk_lookup_run_v6(net, IPPROTO_UDP,
-					    saddr, sport, daddr, hnum, &sk);
+	no_reuseport = bpf_sk_lookup_run_v6(net, IPPROTO_UDP, saddr, sport,
+					    daddr, hnum, dif, &sk);
 	if (no_reuseport || IS_ERR_OR_NULL(sk))
 		return sk;
 
@@ -240,7 +240,7 @@ struct sock *__udp6_lib_lookup(struct net *net,
 	/* Lookup redirect from BPF */
 	if (static_branch_unlikely(&bpf_sk_lookup_enabled)) {
 		sk = udp6_lookup_run_bpf(net, udptable, skb,
-					 saddr, sport, daddr, hnum);
+					 saddr, sport, daddr, hnum, dif);
 		if (sk) {
 			result = sk;
 			goto done;

tools/include/uapi/linux/bpf.h

@@ -6316,6 +6316,7 @@ struct bpf_sk_lookup {
 	__u32 local_ip4;	/* Network byte order */
 	__u32 local_ip6[4];	/* Network byte order */
 	__u32 local_port;	/* Host byte order */
+	__u32 ingress_ifindex;		/* The arriving interface. Determined by inet_iif. */
 };
 
 /*