[PATCH bpf-next v3 05/10] bpf: Add bpf_sock_addr_set() to allow writing sockaddr len from bpf

[Daan De Meyer <daan.j.demeyer@xxxxxxxxx>]

As prep for adding unix socket support to the cgroup sockaddr hooks,
let's add a kfunc bpf_sock_addr_set() that allows modifying the
sockaddr length from bpf. This is required to allow modifying AF_UNIX
sockaddrs correctly.

Signed-off-by: Daan De Meyer <daan.j.demeyer@xxxxxxxxx>
---
 net/core/filter.c | 52 ++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 51 insertions(+), 1 deletion(-)

diff --git a/net/core/filter.c b/net/core/filter.c
index 44fb997434ad..1c656e2d7b58 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -81,6 +81,7 @@
 #include <net/xdp.h>
 #include <net/mptcp.h>
 #include <net/netfilter/nf_conntrack_bpf.h>
+#include <linux/un.h>
 
 static const struct bpf_func_proto *
 bpf_sk_base_func_proto(enum bpf_func_id func_id);
@@ -11670,6 +11671,44 @@ __bpf_kfunc int bpf_dynptr_from_xdp(struct xdp_buff *xdp, u64 flags,
 
 	return 0;
 }
+
+__bpf_kfunc int bpf_sock_addr_set(struct bpf_sock_addr_kern *sa_kern,
+				  const void *addr, u32 addrlen__sz)
+{
+	const struct sockaddr *sa = addr;
+
+	if (addrlen__sz <= offsetof(struct sockaddr, sa_family))
+		return -EINVAL;
+
+	if (addrlen__sz > sizeof(struct sockaddr_storage))
+		return -EINVAL;
+
+	if (sa->sa_family != sa_kern->uaddr->sa_family)
+		return -EINVAL;
+
+	switch (sa->sa_family) {
+	case AF_INET:
+		if (addrlen__sz < sizeof(struct sockaddr_in))
+			return -EINVAL;
+		break;
+	case AF_INET6:
+		if (addrlen__sz < SIN6_LEN_RFC2133)
+			return -EINVAL;
+		break;
+	case AF_UNIX:
+		if (addrlen__sz <= offsetof(struct sockaddr_un, sun_path) ||
+		    addrlen__sz > sizeof(struct sockaddr_un))
+			return -EINVAL;
+		break;
+	default:
+		return -EINVAL;
+	}
+
+	memcpy(sa_kern->uaddr, sa, addrlen__sz);
+	sa_kern->uaddrlen = addrlen__sz;
+
+	return 0;
+}
 __diag_pop();
 
 int bpf_dynptr_from_skb_rdonly(struct sk_buff *skb, u64 flags,
@@ -11694,6 +11733,10 @@ BTF_SET8_START(bpf_kfunc_check_set_xdp)
 BTF_ID_FLAGS(func, bpf_dynptr_from_xdp)
 BTF_SET8_END(bpf_kfunc_check_set_xdp)
 
+BTF_SET8_START(bpf_kfunc_check_set_sock_addr)
+BTF_ID_FLAGS(func, bpf_sock_addr_set)
+BTF_SET8_END(bpf_kfunc_check_set_sock_addr)
+
 static const struct btf_kfunc_id_set bpf_kfunc_set_skb = {
 	.owner = THIS_MODULE,
 	.set = &bpf_kfunc_check_set_skb,
@@ -11704,6 +11747,11 @@ static const struct btf_kfunc_id_set bpf_kfunc_set_xdp = {
 	.set = &bpf_kfunc_check_set_xdp,
 };
 
+static const struct btf_kfunc_id_set bpf_kfunc_set_sock_addr = {
+	.owner = THIS_MODULE,
+	.set = &bpf_kfunc_check_set_sock_addr,
+};
+
 static int __init bpf_kfunc_init(void)
 {
 	int ret;
@@ -11717,6 +11765,8 @@ static int __init bpf_kfunc_init(void)
 	ret = ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_LWT_IN, &bpf_kfunc_set_skb);
 	ret = ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_LWT_XMIT, &bpf_kfunc_set_skb);
 	ret = ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_LWT_SEG6LOCAL, &bpf_kfunc_set_skb);
-	return ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_XDP, &bpf_kfunc_set_xdp);
+	ret = ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_XDP, &bpf_kfunc_set_xdp);
+	return ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_CGROUP_SOCK_ADDR,
+						&bpf_kfunc_set_sock_addr);
 }
 late_initcall(bpf_kfunc_init);
-- 
2.40.0