[PATCH bpf v3 1/2] bpf: reject incompatible socket assignments

[Shihuang Liu <shlomojune6@gmail.com>]

bpf_sk_assign() permits TC ingress programs to associate an IPv6 packet
with an AF_INET socket. The receive path can then interpret IPv6 skb
control data as IPv4 metadata. When IP_RETOPTS is enabled, this can cause
__ip_options_echo() to copy beyond its stack buffer.

Reject incompatible packet and socket families before attaching the socket,
while preserving IPv4 assignments to dual-stack AF_INET6 sockets. Validate
request, mapped, and time-wait sockets using their effective family.

Use the packet's effective protocol for VLAN checks and share the same
predicate across bpf_sk_assign() and bpf_sk_assign_tcp_reqsk().

Fixes: cf7fbe660f2d ("bpf: Add socket assign support")
Assisted-by: LLM
Signed-off-by: Shihuang Liu <shlomojune6@gmail.com>
---
Changes since v2:
- Use the effective packet protocol for VLAN-aware family validation.
- Handle IPv4-mapped AF_INET6 sockets, TCP children, and TIME_WAIT sockets.
- Share the protocol-based check with bpf_sk_assign_tcp_reqsk().

v2:
https://lore.kernel.org/netdev/20260911172313.64009-1-shlomojune6@gmail.com/

Changes since v1:
- Move family validation out of the IPv6 receive fast path and into
  bpf_sk_assign() and bpf_sk_assign_tcp_reqsk().
- Preserve IPv4 assignments to dual-stack AF_INET6 sockets.
- Check request sockets using rsk_ops->family.
- Split the fix into two patches and target the BPF fixes tree.

v1:
https://lore.kernel.org/netdev/20260823101809.26802-1-shlomojune6@gmail.com/
---
 include/uapi/linux/bpf.h       |  4 +++
 net/core/filter.c              | 63 ++++++++++++++++++++++++++++++++++
 tools/include/uapi/linux/bpf.h |  4 +++
 3 files changed, 71 insertions(+)

diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 732b35cc08d1c..5d8f5e2c8db38 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -4568,6 +4568,10 @@ union bpf_attr {
  *		**-EOPNOTSUPP** if the operation is not supported, for example
  *		a call from outside of TC ingress.
  *
+ *		**-EAFNOSUPPORT** if the socket family is not compatible with
+ *		the network layer of the packet, for example an **AF_INET**
+ *		socket and an IPv6 packet.
+ *
  * long bpf_sk_assign(struct bpf_sk_lookup *ctx, struct bpf_sock *sk, u64 flags)
  *	Description
  *		Helper is overloaded depending on BPF program type. This
diff --git a/net/core/filter.c b/net/core/filter.c
index 61940e7535523..5f64065523584 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -3491,6 +3491,64 @@ static int bpf_skb_proto_xlat(struct sk_buff *skb, __be16 to_proto)
 	return -ENOTSUPP;
 }
 
+static bool bpf_sk_assign_family_ok_proto(const struct sock *sk, __be16 proto)
+{
+	const struct inet_connection_sock_af_ops *af_ops;
+	unsigned short family;
+
+	switch (proto) {
+	case htons(ETH_P_IP):
+		family = AF_INET;
+		break;
+	case htons(ETH_P_IPV6):
+		family = AF_INET6;
+		break;
+	default:
+		return true;
+	}
+
+	/* Requests inherit the listener family, but have family-specific ops. */
+	if (sk->sk_state == TCP_NEW_SYN_RECV)
+		return inet_reqsk(sk)->rsk_ops->family == family;
+
+	/* A dual-stack listener accepts both packet families. */
+	if (sk->sk_state == TCP_LISTEN && sk->sk_family == AF_INET6)
+		return family == AF_INET6 || !ipv6_only_sock(sk);
+
+#if IS_ENABLED(CONFIG_IPV6)
+	/* IPv4-mapped and pure IPv6 time-wait sockets retain AF_INET6. */
+	if (sk->sk_state == TCP_TIME_WAIT && sk->sk_family == AF_INET6) {
+		const struct inet_timewait_sock *tw = inet_twsk(sk);
+		bool mapped;
+
+		mapped = ipv6_addr_v4mapped(&tw->tw_v6_daddr) &&
+			 ipv6_addr_v4mapped(&tw->tw_v6_rcv_saddr);
+		return family == (mapped ? AF_INET : AF_INET6);
+	}
+#endif
+
+	/* IPv4-mapped and pure IPv6 TCP children keep AF_INET6 in sk_family. */
+	if (sk_fullsock(sk) && sk->sk_family == AF_INET6 && sk_is_tcp(sk)) {
+		af_ops = READ_ONCE(inet_csk(sk)->icsk_af_ops);
+		if ((family == AF_INET6 &&
+		     af_ops->net_header_len == sizeof(struct iphdr)) ||
+		    (family == AF_INET &&
+		     af_ops->net_header_len == sizeof(struct ipv6hdr)))
+			return false;
+	}
+
+	return sk->sk_family == family ||
+	       (family == AF_INET &&
+		sk->sk_family == AF_INET6 &&
+		!ipv6_only_sock(sk));
+}
+
+static bool bpf_sk_assign_family_ok(const struct sk_buff *skb,
+				    const struct sock *sk)
+{
+	return bpf_sk_assign_family_ok_proto(sk, skb_protocol(skb, true));
+}
+
 BPF_CALL_3(bpf_skb_change_proto, struct sk_buff *, skb, __be16, proto,
 	   u64, flags)
 {
@@ -7989,6 +8047,8 @@ BPF_CALL_3(bpf_sk_assign, struct sk_buff *, skb, struct sock *, sk, u64, flags)
 		return -ENETUNREACH;
 	if (sk_unhashed(sk))
 		return -EOPNOTSUPP;
+	if (!bpf_sk_assign_family_ok(skb, sk))
+		return -EAFNOSUPPORT;
 	if (sk_is_refcounted(sk) &&
 	    unlikely(!refcount_inc_not_zero(&sk->sk_refcnt)))
 		return -ENOENT;
@@ -12526,6 +12586,9 @@ __bpf_kfunc int bpf_sk_assign_tcp_reqsk(struct __sk_buff *s, struct sock *sk,
 	if (net != sock_net(sk))
 		return -ENETUNREACH;
 
+	if (!bpf_sk_assign_family_ok(skb, sk))
+		return -EAFNOSUPPORT;
+
 	switch (skb->protocol) {
 	case htons(ETH_P_IP):
 		ops = &tcp_request_sock_ops;
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index 732b35cc08d1c..5d8f5e2c8db38 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -4568,6 +4568,10 @@ union bpf_attr {
  *		**-EOPNOTSUPP** if the operation is not supported, for example
  *		a call from outside of TC ingress.
  *
+ *		**-EAFNOSUPPORT** if the socket family is not compatible with
+ *		the network layer of the packet, for example an **AF_INET**
+ *		socket and an IPv6 packet.
+ *
  * long bpf_sk_assign(struct bpf_sk_lookup *ctx, struct bpf_sock *sk, u64 flags)
  *	Description
  *		Helper is overloaded depending on BPF program type. This
-- 
2.43.0