[PATCH bpf v2 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 in bpf_sk_assign() and
bpf_sk_assign_tcp_reqsk(). Continue to allow IPv4 packets to use
dual-stack AF_INET6 sockets.

Check request sockets against rsk_ops->family, since their sk_family is
inherited from the listener and sk_ipv6only is not initialized.

Fixes: cf7fbe660f2d ("bpf: Add socket assign support")
Assisted-by: LLM
Signed-off-by: Shihuang Liu <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              | 31 +++++++++++++++++++++++++++++++
 tools/include/uapi/linux/bpf.h |  4 ++++
 3 files changed, 39 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..e9cc76b775c0c 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -3491,6 +3491,32 @@ static int bpf_skb_proto_xlat(struct sk_buff *skb, __be16 to_proto)
 	return -ENOTSUPP;
 }
 
+static bool bpf_sk_assign_family_ok(const struct sk_buff *skb,
+				    const struct sock *sk)
+{
+	unsigned short family;
+
+	switch (skb->protocol) {
+	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;
+
+	return sk->sk_family == family ||
+	       (family == AF_INET &&
+		sk->sk_family == AF_INET6 &&
+		!ipv6_only_sock(sk));
+}
+
 BPF_CALL_3(bpf_skb_change_proto, struct sk_buff *, skb, __be16, proto,
 	   u64, flags)
 {
@@ -7989,6 +8015,8 @@ 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 +12554,9 @@ __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