bpf: Add support for passing mark with bpf_fib_lookup

Extend the bpf_fib_lookup() helper by making it to utilize mark if
the BPF_FIB_LOOKUP_MARK flag is set. In order to pass the mark the
four bytes of struct bpf_fib_lookup are used, shared with the
output-only smac/dmac fields.
Signed-off-by: Anton Protopopov <aspsk@isovalent.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Reviewed-by: David Ahern <dsahern@kernel.org>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20240326101742.17421-2-aspsk@isovalent.comSigned-off-by: Alexei Starovoitov <ast@kernel.org>

include/uapi/linux/bpf.h

@@ -3394,6 +3394,10 @@ union bpf_attr {
  *			for the nexthop. If the src addr cannot be derived,
  *			**BPF_FIB_LKUP_RET_NO_SRC_ADDR** is returned. In this
  *			case, *params*->dmac and *params*->smac are not set either.
+ *		**BPF_FIB_LOOKUP_MARK**
+ *			Use the mark present in *params*->mark for the fib lookup.
+ *			This option should not be used with BPF_FIB_LOOKUP_DIRECT,
+ *			as it only has meaning for full lookups.
  *
  *		*ctx* is either **struct xdp_md** for XDP programs or
  *		**struct sk_buff** tc cls_act programs.
@@ -7120,6 +7124,7 @@ enum {
 	BPF_FIB_LOOKUP_SKIP_NEIGH = (1U << 2),
 	BPF_FIB_LOOKUP_TBID    = (1U << 3),
 	BPF_FIB_LOOKUP_SRC     = (1U << 4),
+	BPF_FIB_LOOKUP_MARK    = (1U << 5),
 };
 
 enum {
@@ -7197,8 +7202,19 @@ struct bpf_fib_lookup {
 		__u32	tbid;
 	};
 
-	__u8	smac[6];     /* ETH_ALEN */
-	__u8	dmac[6];     /* ETH_ALEN */
+	union {
+		/* input */
+		struct {
+			__u32	mark;   /* policy routing */
+			/* 2 4-byte holes for input */
+		};
+
+		/* output: source and dest mac */
+		struct {
+			__u8	smac[6];	/* ETH_ALEN */
+			__u8	dmac[6];	/* ETH_ALEN */
+		};
+	};
 };
 
 struct bpf_redir_neigh {

net/core/filter.c

@@ -5884,7 +5884,10 @@ static int bpf_ipv4_fib_lookup(struct net *net, struct bpf_fib_lookup *params,
 
 		err = fib_table_lookup(tb, &fl4, &res, FIB_LOOKUP_NOREF);
 	} else {
-		fl4.flowi4_mark = 0;
+		if (flags & BPF_FIB_LOOKUP_MARK)
+			fl4.flowi4_mark = params->mark;
+		else
+			fl4.flowi4_mark = 0;
 		fl4.flowi4_secid = 0;
 		fl4.flowi4_tun_key.tun_id = 0;
 		fl4.flowi4_uid = sock_net_uid(net, NULL);
@@ -6027,7 +6030,10 @@ static int bpf_ipv6_fib_lookup(struct net *net, struct bpf_fib_lookup *params,
 		err = ipv6_stub->fib6_table_lookup(net, tb, oif, &fl6, &res,
 						   strict);
 	} else {
-		fl6.flowi6_mark = 0;
+		if (flags & BPF_FIB_LOOKUP_MARK)
+			fl6.flowi6_mark = params->mark;
+		else
+			fl6.flowi6_mark = 0;
 		fl6.flowi6_secid = 0;
 		fl6.flowi6_tun_key.tun_id = 0;
 		fl6.flowi6_uid = sock_net_uid(net, NULL);
@@ -6105,7 +6111,7 @@ static int bpf_ipv6_fib_lookup(struct net *net, struct bpf_fib_lookup *params,
 
 #define BPF_FIB_LOOKUP_MASK (BPF_FIB_LOOKUP_DIRECT | BPF_FIB_LOOKUP_OUTPUT | \
 			     BPF_FIB_LOOKUP_SKIP_NEIGH | BPF_FIB_LOOKUP_TBID | \
-			     BPF_FIB_LOOKUP_SRC)
+			     BPF_FIB_LOOKUP_SRC | BPF_FIB_LOOKUP_MARK)
 
 BPF_CALL_4(bpf_xdp_fib_lookup, struct xdp_buff *, ctx,
 	   struct bpf_fib_lookup *, params, int, plen, u32, flags)

tools/include/uapi/linux/bpf.h

@@ -3394,6 +3394,10 @@ union bpf_attr {
  *			for the nexthop. If the src addr cannot be derived,
  *			**BPF_FIB_LKUP_RET_NO_SRC_ADDR** is returned. In this
  *			case, *params*->dmac and *params*->smac are not set either.
+ *		**BPF_FIB_LOOKUP_MARK**
+ *			Use the mark present in *params*->mark for the fib lookup.
+ *			This option should not be used with BPF_FIB_LOOKUP_DIRECT,
+ *			as it only has meaning for full lookups.
  *
  *		*ctx* is either **struct xdp_md** for XDP programs or
  *		**struct sk_buff** tc cls_act programs.
@@ -7120,6 +7124,7 @@ enum {
 	BPF_FIB_LOOKUP_SKIP_NEIGH = (1U << 2),
 	BPF_FIB_LOOKUP_TBID    = (1U << 3),
 	BPF_FIB_LOOKUP_SRC     = (1U << 4),
+	BPF_FIB_LOOKUP_MARK    = (1U << 5),
 };
 
 enum {
@@ -7197,8 +7202,19 @@ struct bpf_fib_lookup {
 		__u32	tbid;
 	};
 
-	__u8	smac[6];     /* ETH_ALEN */
-	__u8	dmac[6];     /* ETH_ALEN */
+	union {
+		/* input */
+		struct {
+			__u32	mark;   /* policy routing */
+			/* 2 4-byte holes for input */
+		};
+
+		/* output: source and dest mac */
+		struct {
+			__u8	smac[6];	/* ETH_ALEN */
+			__u8	dmac[6];	/* ETH_ALEN */
+		};
+	};
 };
 
 struct bpf_redir_neigh {