[PATCH bpf-next v2 1/3] bpf: add bpf_ksock_sendto() kfunc

[Mahe Tardy <mahe.tardy@gmail.com>]

The motivation is to plumb more of the socket API into ksock, thus
supporting sendto() in addition to send() which makes a lot of sense in
the context of UDP sockets which are the only type currently supported.
This is useful when ksock is used to reply to specific addresses or send
to multiple addresses.

Signed-off-by: Mahe Tardy <mahe.tardy@gmail.com>
---
 net/core/bpf_ksock.c | 96 +++++++++++++++++++++++++++++++-------------
 1 file changed, 69 insertions(+), 27 deletions(-)

diff --git a/net/core/bpf_ksock.c b/net/core/bpf_ksock.c
index 48a2e2327ace..37168f43c16c 100644
--- a/net/core/bpf_ksock.c
+++ b/net/core/bpf_ksock.c
@@ -37,6 +37,49 @@ static void ksock_release_work_fn(struct work_struct *work)
 	kfree(ks);
 }

+static int bpf_ksock_addr_to_sockaddr(const union bpf_ksock_addr *addr,
+				      u32 addr_sz, struct sockaddr_storage *sa)
+{
+	if (!addr || addr_sz != sizeof(*addr))
+		return -EINVAL;
+
+	/* Kfunc memory arguments may be unaligned. */
+	memcpy(sa, addr, sizeof(*addr));
+
+	switch (sa->ss_family) {
+	case AF_INET:
+		return sizeof(struct sockaddr_in);
+	case AF_INET6:
+		return sizeof(struct sockaddr_in6);
+	default:
+		return -EAFNOSUPPORT;
+	}
+}
+
+static int ksock_sendto(struct bpf_ksock *ks, const void *data, u32 data_sz,
+			const union bpf_ksock_addr *addr, u32 addr_sz)
+{
+	struct sockaddr_storage sa;
+	struct msghdr msg = {
+		.msg_flags = MSG_DONTWAIT,
+	};
+	struct kvec iov = {
+		.iov_base = (void *)data,
+		.iov_len = data_sz,
+	};
+	int addrlen;
+
+	if (addr) {
+		addrlen = bpf_ksock_addr_to_sockaddr(addr, addr_sz, &sa);
+		if (addrlen < 0)
+			return addrlen;
+		msg.msg_name = &sa;
+		msg.msg_namelen = addrlen;
+	}
+
+	return kernel_sendmsg(ks->sock, &msg, &iov, 1, data_sz);
+}
+
 __bpf_kfunc_start_defs();

 /**
@@ -155,22 +198,9 @@ __bpf_kfunc int bpf_ksock_connect(struct bpf_ksock *ks,
 	struct sockaddr_storage sa;
 	int addrlen;

-	if (!addr || addr__sz != sizeof(*addr))
-		return -EINVAL;
-
-	/* Kfunc memory arguments may be unaligned. */
-	memcpy(&sa, addr, sizeof(*addr));
-
-	switch (sa.ss_family) {
-	case AF_INET:
-		addrlen = sizeof(struct sockaddr_in);
-		break;
-	case AF_INET6:
-		addrlen = sizeof(struct sockaddr_in6);
-		break;
-	default:
-		return -EAFNOSUPPORT;
-	}
+	addrlen = bpf_ksock_addr_to_sockaddr(addr, addr__sz, &sa);
+	if (addrlen < 0)
+		return addrlen;

 	return connect_socket(ks->sock, &sa, addrlen, 0);
 }
@@ -225,18 +255,29 @@ CFI_NOSEAL(bpf_ksock_release_dtor);
 __bpf_kfunc int bpf_ksock_send(struct bpf_ksock *ks, const void *data,
 			       u32 data__sz)
 {
-	struct msghdr msg = {
-		.msg_flags = MSG_DONTWAIT,
-	};
-	struct kvec iov = {
-		.iov_base = (void *)data,
-		.iov_len = data__sz,
-	};
-	int ret;
-
-	ret = kernel_sendmsg(ks->sock, &msg, &iov, 1, data__sz);
+	return ksock_sendto(ks, data, data__sz, NULL, 0);
+}

-	return ret;
+/**
+ * bpf_ksock_sendto() - Send data through a BPF kernel socket to a remote address.
+ * @ks:		The BPF kernel socket context. Must be an acquired reference.
+ * @data:	Pointer to the data to send.
+ * @data__sz:	Size of the data to send.
+ * @addr__nullable: Pointer to an IPv4 or IPv6 socket address, or NULL to use
+ *		   the connected destination.
+ * @addr__sz:	Size of the address union, ignored when the address is NULL.
+ *
+ * Sends data to the specified address, or to the connected destination when
+ * the address is NULL, best-effort and nonblocking. This may sleep
+ * (kernel_sendmsg), so it can only be called from sleepable BPF programs.
+ *
+ * Return: Number of bytes sent on success, negative errno on error.
+ */
+__bpf_kfunc int bpf_ksock_sendto(struct bpf_ksock *ks, const void *data, u32 data__sz,
+				 const union bpf_ksock_addr *addr__nullable,
+				 u32 addr__sz)
+{
+	return ksock_sendto(ks, data, data__sz, addr__nullable, addr__sz);
 }

 __bpf_kfunc_end_defs();
@@ -255,6 +296,7 @@ BTF_KFUNCS_START(ksock_kfunc_btf_ids)
 BTF_ID_FLAGS(func, bpf_ksock_release, KF_RELEASE)
 BTF_ID_FLAGS(func, bpf_ksock_acquire, KF_ACQUIRE | KF_RCU | KF_RET_NULL)
 BTF_ID_FLAGS(func, bpf_ksock_send, KF_SLEEPABLE)
+BTF_ID_FLAGS(func, bpf_ksock_sendto, KF_SLEEPABLE)
 BTF_KFUNCS_END(ksock_kfunc_btf_ids)

 #ifdef CONFIG_BPF_LSM
--
2.43.0