udp: seq_file: Remove bpf_seq_afinfo from udp_iter_state

This is a preparatory commit to remove the field. The field was
previously shared between proc fs and BPF UDP socket iterators. As the
follow-up commits will decouple the implementation for the iterators,
remove the field. As for BPF socket iterator, filtering of sockets is
exepected to be done in BPF programs.

Suggested-by: Martin KaFai Lau <martin.lau@kernel.org>
Signed-off-by: Aditi Ghag <aditi.ghag@isovalent.com>
Link: https://lore.kernel.org/r/20230519225157.760788-5-aditi.ghag@isovalent.com
Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>

Author: aditighag

include/net/udp.h

@@ -437,7 +437,6 @@ struct udp_seq_afinfo {
 struct udp_iter_state {
 	struct seq_net_private  p;
 	int			bucket;
-	struct udp_seq_afinfo	*bpf_seq_afinfo;
 };
 
 void *udp_seq_start(struct seq_file *seq, loff_t *pos);

net/ipv4/udp.c

@@ -2998,14 +2998,18 @@ static bool seq_sk_match(struct seq_file *seq, const struct sock *sk)
 		net_eq(sock_net(sk), seq_file_net(seq)));
 }
 
+#ifdef CONFIG_BPF_SYSCALL
+static const struct seq_operations bpf_iter_udp_seq_ops;
+#endif
 static struct udp_table *udp_get_table_seq(struct seq_file *seq,
 					   struct net *net)
 {
-	const struct udp_iter_state *state = seq->private;
 	const struct udp_seq_afinfo *afinfo;
 
-	if (state->bpf_seq_afinfo)
+#ifdef CONFIG_BPF_SYSCALL
+	if (seq->op == &bpf_iter_udp_seq_ops)
 		return net->ipv4.udp_table;
+#endif
 
 	afinfo = pde_data(file_inode(seq->file));
 	return afinfo->udp_table ? : net->ipv4.udp_table;
@@ -3429,28 +3433,11 @@ DEFINE_BPF_ITER_FUNC(udp, struct bpf_iter_meta *meta,
 
 static int bpf_iter_init_udp(void *priv_data, struct bpf_iter_aux_info *aux)
 {
-	struct udp_iter_state *st = priv_data;
-	struct udp_seq_afinfo *afinfo;
-	int ret;
-
-	afinfo = kmalloc(sizeof(*afinfo), GFP_USER | __GFP_NOWARN);
-	if (!afinfo)
-		return -ENOMEM;
-
-	afinfo->family = AF_UNSPEC;
-	afinfo->udp_table = NULL;
-	st->bpf_seq_afinfo = afinfo;
-	ret = bpf_iter_init_seq_net(priv_data, aux);
-	if (ret)
-		kfree(afinfo);
-	return ret;
+	return bpf_iter_init_seq_net(priv_data, aux);
 }
 
 static void bpf_iter_fini_udp(void *priv_data)
 {
-	struct udp_iter_state *st = priv_data;
-
-	kfree(st->bpf_seq_afinfo);
 	bpf_iter_fini_seq_net(priv_data);
 }