SUNRPC: Capture CMSG metadata on client-side receive

kTLS sockets use CMSG to report decryption errors and the need
for session re-keying.

For RPC-with-TLS, an "application data" message contains a ULP
payload, and that is passed along to the RPC client. An "alert"
message triggers connection reset. Everything else is discarded.

Signed-off-by: Chuck Lever <[e-mail]>
Reviewed-by: Jeff Layton <[e-mail]>
Signed-off-by: Trond Myklebust <[e-mail]>

net/sunrpc/xprtsock.c

···
 #include <net/checksum.h>
 #include <net/udp.h>
 #include <net/tcp.h>
+#include <net/tls.h>
+
 #include <linux/bvec.h>
 #include <linux/highmem.h>
 #include <linux/uio.h>
···
 	return want;
 }
 
+static int
+xs_sock_process_cmsg(struct socket *sock, struct msghdr *msg,
+		     struct cmsghdr *cmsg, int ret)
+{
+	if (cmsg->cmsg_level == SOL_TLS &&
+	    cmsg->cmsg_type == TLS_GET_RECORD_TYPE) {
+		u8 content_type = *((u8 *)CMSG_DATA(cmsg));
+
+		switch (content_type) {
+		case TLS_RECORD_TYPE_DATA:
+			/* TLS sets EOR at the end of each application data
+			 * record, even though there might be more frames
+			 * waiting to be decrypted.
+			 */
+			msg->msg_flags &= ~MSG_EOR;
+			break;
+		case TLS_RECORD_TYPE_ALERT:
+			ret = -ENOTCONN;
+			break;
+		default:
+			ret = -EAGAIN;
+		}
+	}
+	return ret;
+}
+
+static int
+xs_sock_recv_cmsg(struct socket *sock, struct msghdr *msg, int flags)
+{
+	union {
+		struct cmsghdr	cmsg;
+		u8		buf[CMSG_SPACE(sizeof(u8))];
+	} u;
+	int ret;
+
+	msg->msg_control = &u;
+	msg->msg_controllen = sizeof(u);
+	ret = sock_recvmsg(sock, msg, flags);
+	if (msg->msg_controllen != sizeof(u))
+		ret = xs_sock_process_cmsg(sock, msg, &u.cmsg, ret);
+	return ret;
+}
+
 static ssize_t
 xs_sock_recvmsg(struct socket *sock, struct msghdr *msg, int flags, size_t seek)
 {
 	ssize_t ret;
 	if (seek != 0)
 		iov_iter_advance(&msg->msg_iter, seek);
-	ret = sock_recvmsg(sock, msg, flags);
+	ret = xs_sock_recv_cmsg(sock, msg, flags);
 	return ret > 0 ? ret + seek : ret;
 }
 
···
 		size_t count)
 {
 	iov_iter_discard(&msg->msg_iter, ITER_DEST, count);
-	return sock_recvmsg(sock, msg, flags);
+	return xs_sock_recv_cmsg(sock, msg, flags);
 }
 
 #if ARCH_IMPLEMENTS_FLUSH_DCACHE_PAGE