skmsg: use skb ext instead of TCP_SKB_CB

Currently TCP_SKB_CB() is hard-coded in skmsg code, it certainly
does not work for any other non-TCP protocols. We can move them to
skb ext instead of playing with skb cb, which is harder to make
correct.

Cc: John Fastabend <john.fastabend@gmail.com>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Cc: Jakub Sitnicki <jakub@cloudflare.com>
Cc: Lorenz Bauer <lmb@cloudflare.com>
Signed-off-by: Cong Wang <cong.wang@bytedance.com>

include/linux/skbuff.h

@@ -4166,6 +4166,9 @@ enum skb_ext_id {
 #endif
 #if IS_ENABLED(CONFIG_MPTCP)
 	SKB_EXT_MPTCP,
+#endif
+#if IS_ENABLED(CONFIG_NET_SOCK_MSG)
+	SKB_EXT_BPF,
 #endif
 	SKB_EXT_NUM, /* must be last */
 };

include/linux/skmsg.h

@@ -453,4 +453,44 @@ static inline bool sk_psock_strp_enabled(struct sk_psock *psock)
 		return false;
 	return !!psock->saved_data_ready;
 }
+
+struct skb_bpf_ext {
+	__u32 flags;
+	struct sock *sk_redir;
+};
+
+#if IS_ENABLED(CONFIG_NET_SOCK_MSG)
+static inline
+bool skb_bpf_ext_ingress(const struct sk_buff *skb)
+{
+	struct skb_bpf_ext *ext = skb_ext_find(skb, SKB_EXT_BPF);
+
+	return ext->flags & BPF_F_INGRESS;
+}
+
+static inline
+void skb_bpf_ext_set_ingress(const struct sk_buff *skb)
+{
+	struct skb_bpf_ext *ext = skb_ext_find(skb, SKB_EXT_BPF);
+
+	ext->flags |= BPF_F_INGRESS;
+}
+
+static inline
+struct sock *skb_bpf_ext_redirect_fetch(struct sk_buff *skb)
+{
+	struct skb_bpf_ext *ext = skb_ext_find(skb, SKB_EXT_BPF);
+
+	return ext->sk_redir;
+}
+
+static inline
+void skb_bpf_ext_redirect_clear(struct sk_buff *skb)
+{
+	struct skb_bpf_ext *ext = skb_ext_find(skb, SKB_EXT_BPF);
+
+	ext->flags = 0;
+	ext->sk_redir = NULL;
+}
+#endif /* CONFIG_NET_SOCK_MSG */
 #endif /* _LINUX_SKMSG_H */

include/net/tcp.h

@@ -882,30 +882,11 @@ struct tcp_skb_cb {
 			struct inet6_skb_parm	h6;
 #endif
 		} header;	/* For incoming skbs */
-		struct {
-			__u32 flags;
-			struct sock *sk_redir;
-		} bpf;
 	};
 };
 
 #define TCP_SKB_CB(__skb)	((struct tcp_skb_cb *)&((__skb)->cb[0]))
 
-static inline bool tcp_skb_bpf_ingress(const struct sk_buff *skb)
-{
-	return TCP_SKB_CB(skb)->bpf.flags & BPF_F_INGRESS;
-}
-
-static inline struct sock *tcp_skb_bpf_redirect_fetch(struct sk_buff *skb)
-{
-	return TCP_SKB_CB(skb)->bpf.sk_redir;
-}
-
-static inline void tcp_skb_bpf_redirect_clear(struct sk_buff *skb)
-{
-	TCP_SKB_CB(skb)->bpf.sk_redir = NULL;
-}
-
 extern const struct inet_connection_sock_af_ops ipv4_specific;
 
 #if IS_ENABLED(CONFIG_IPV6)

net/Kconfig

@@ -419,6 +419,7 @@ config SOCK_VALIDATE_XMIT
 
 config NET_SOCK_MSG
 	bool
+	select SKB_EXTENSIONS
 	default n
 	help
 	  The NET_SOCK_MSG provides a framework for plain sockets (e.g. TCP) or

net/core/skbuff.c

@@ -60,6 +60,7 @@
 #include <linux/prefetch.h>
 #include <linux/if_vlan.h>
 #include <linux/mpls.h>
+#include <linux/skmsg.h>
 
 #include <net/protocol.h>
 #include <net/dst.h>
@@ -4259,6 +4260,9 @@ static const u8 skb_ext_type_len[] = {
 #if IS_ENABLED(CONFIG_MPTCP)
 	[SKB_EXT_MPTCP] = SKB_EXT_CHUNKSIZEOF(struct mptcp_ext),
 #endif
+#if IS_ENABLED(CONFIG_NET_SOCK_MSG)
+	[SKB_EXT_BPF] = SKB_EXT_CHUNKSIZEOF(struct skb_bpf_ext),
+#endif
 };
 
 static __always_inline unsigned int skb_ext_total_length(void)
@@ -4275,6 +4279,9 @@ static __always_inline unsigned int skb_ext_total_length(void)
 #endif
 #if IS_ENABLED(CONFIG_MPTCP)
 		skb_ext_type_len[SKB_EXT_MPTCP] +
+#endif
+#if IS_ENABLED(CONFIG_NET_SOCK_MSG)
+		skb_ext_type_len[SKB_EXT_BPF] +
 #endif
 		0;
 }

net/core/skmsg.c

@@ -525,7 +525,8 @@ static void sk_psock_backlog(struct work_struct *work)
 		len = skb->len;
 		off = 0;
 start:
-		ingress = tcp_skb_bpf_ingress(skb);
+		ingress = skb_bpf_ext_ingress(skb);
+		skb_ext_del(skb, SKB_EXT_BPF);
 		do {
 			ret = -EIO;
 			if (likely(psock->sk->sk_socket))
@@ -755,7 +756,7 @@ static void sk_psock_skb_redirect(struct sk_buff *skb)
 	struct sk_psock *psock_other;
 	struct sock *sk_other;
 
-	sk_other = tcp_skb_bpf_redirect_fetch(skb);
+	sk_other = skb_bpf_ext_redirect_fetch(skb);
 	/* This error is a buggy BPF program, it returned a redirect
 	 * return code, but then didn't set a redirect interface.
 	 */
@@ -797,6 +798,9 @@ int sk_psock_tls_strp_read(struct sk_psock *psock, struct sk_buff *skb)
 	struct bpf_prog *prog;
 	int ret = __SK_PASS;
 
+	if (!skb_ext_add(skb, SKB_EXT_BPF))
+		return __SK_DROP;
+
 	rcu_read_lock();
 	prog = READ_ONCE(psock->progs.skb_verdict);
 	if (likely(prog)) {
@@ -805,9 +809,9 @@ int sk_psock_tls_strp_read(struct sk_psock *psock, struct sk_buff *skb)
 		 * TLS context.
 		 */
 		skb->sk = psock->sk;
-		tcp_skb_bpf_redirect_clear(skb);
+		skb_bpf_ext_redirect_clear(skb);
 		ret = sk_psock_bpf_run(psock, prog, skb);
-		ret = sk_psock_map_verd(ret, tcp_skb_bpf_redirect_fetch(skb));
+		ret = sk_psock_map_verd(ret, skb_bpf_ext_redirect_fetch(skb));
 		skb->sk = NULL;
 	}
 	sk_psock_tls_verdict_apply(skb, psock->sk, ret);
@@ -819,7 +823,6 @@ EXPORT_SYMBOL_GPL(sk_psock_tls_strp_read);
 static void sk_psock_verdict_apply(struct sk_psock *psock,
 				   struct sk_buff *skb, int verdict)
 {
-	struct tcp_skb_cb *tcp;
 	struct sock *sk_other;
 	int err = -EIO;
 
@@ -831,9 +834,7 @@ static void sk_psock_verdict_apply(struct sk_psock *psock,
 			goto out_free;
 		}
 
-		tcp = TCP_SKB_CB(skb);
-		tcp->bpf.flags |= BPF_F_INGRESS;
-
+		skb_bpf_ext_set_ingress(skb);
 		/* If the queue is empty then we can submit directly
 		 * into the msg queue. If its not empty we have to
 		 * queue work otherwise we may get OOO data. Otherwise,
@@ -891,11 +892,15 @@ static void sk_psock_strp_read(struct strparser *strp, struct sk_buff *skb)
 		goto out;
 	}
 	skb_set_owner_r(skb, sk);
+	if (!skb_ext_add(skb, SKB_EXT_BPF)) {
+		kfree_skb(skb);
+		goto out;
+	}
 	prog = READ_ONCE(psock->progs.skb_verdict);
 	if (likely(prog)) {
-		tcp_skb_bpf_redirect_clear(skb);
+		skb_bpf_ext_redirect_clear(skb);
 		ret = sk_psock_bpf_run(psock, prog, skb);
-		ret = sk_psock_map_verd(ret, tcp_skb_bpf_redirect_fetch(skb));
+		ret = sk_psock_map_verd(ret, skb_bpf_ext_redirect_fetch(skb));
 	}
 	sk_psock_verdict_apply(psock, skb, ret);
 out:
@@ -999,11 +1004,17 @@ static int sk_psock_verdict_recv(read_descriptor_t *desc, struct sk_buff *skb,
 		goto out;
 	}
 	skb_set_owner_r(skb, sk);
+	if (!skb_ext_add(skb, SKB_EXT_BPF)) {
+		len = 0;
+		kfree_skb(skb);
+		goto out;
+	}
+
 	prog = READ_ONCE(psock->progs.skb_verdict);
 	if (likely(prog)) {
-		tcp_skb_bpf_redirect_clear(skb);
+		skb_bpf_ext_redirect_clear(skb);
 		ret = sk_psock_bpf_run(psock, prog, skb);
-		ret = sk_psock_map_verd(ret, tcp_skb_bpf_redirect_fetch(skb));
+		ret = sk_psock_map_verd(ret, skb_bpf_ext_redirect_fetch(skb));
 	}
 	sk_psock_verdict_apply(psock, skb, ret);
 out:

net/core/sock_map.c

@@ -657,7 +657,7 @@ const struct bpf_func_proto bpf_sock_map_update_proto = {
 BPF_CALL_4(bpf_sk_redirect_map, struct sk_buff *, skb,
 	   struct bpf_map *, map, u32, key, u64, flags)
 {
-	struct tcp_skb_cb *tcb = TCP_SKB_CB(skb);
+	struct skb_bpf_ext *ext = skb_ext_find(skb, SKB_EXT_BPF);
 	struct sock *sk;
 
 	if (unlikely(flags & ~(BPF_F_INGRESS)))
@@ -667,8 +667,8 @@ BPF_CALL_4(bpf_sk_redirect_map, struct sk_buff *, skb,
 	if (unlikely(!sk || !sock_map_redirect_allowed(sk)))
 		return SK_DROP;
 
-	tcb->bpf.flags = flags;
-	tcb->bpf.sk_redir = sk;
+	ext->flags = flags;
+	ext->sk_redir = sk;
 	return SK_PASS;
 }
 
@@ -1250,7 +1250,7 @@ const struct bpf_func_proto bpf_sock_hash_update_proto = {
 BPF_CALL_4(bpf_sk_redirect_hash, struct sk_buff *, skb,
 	   struct bpf_map *, map, void *, key, u64, flags)
 {
-	struct tcp_skb_cb *tcb = TCP_SKB_CB(skb);
+	struct skb_bpf_ext *ext = skb_ext_find(skb, SKB_EXT_BPF);
 	struct sock *sk;
 
 	if (unlikely(flags & ~(BPF_F_INGRESS)))
@@ -1260,8 +1260,8 @@ BPF_CALL_4(bpf_sk_redirect_hash, struct sk_buff *, skb,
 	if (unlikely(!sk || !sock_map_redirect_allowed(sk)))
 		return SK_DROP;
 
-	tcb->bpf.flags = flags;
-	tcb->bpf.sk_redir = sk;
+	ext->flags = flags;
+	ext->sk_redir = sk;
 	return SK_PASS;
 }