io_uring: Introduce getsockname io_uring cmd

Introduce a socket-specific io_uring_cmd to support
getsockname/getpeername via io_uring.  I made this an io_uring_cmd
instead of a new operation to avoid polluting the command namespace with
what is exclusively a socket operation.  In addition, since we don't
need to conform to existing interfaces, this merges the
getsockname/getpeername in a single operation, since the implementation
is pretty much the same.

This has been frequently requested, for instance at [1] and more
recently in the project Discord channel. The main use-case is to support
fixed socket file descriptors.

[1] axboe/liburing#1356

Signed-off-by: Gabriel Krisman Bertazi <krisman@suse.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

Author: krisman

include/uapi/linux/io_uring.h

@@ -1009,6 +1009,7 @@ enum io_uring_socket_op {
 	SOCKET_URING_OP_GETSOCKOPT,
 	SOCKET_URING_OP_SETSOCKOPT,
 	SOCKET_URING_OP_TX_TIMESTAMP,
+	SOCKET_URING_OP_GETSOCKNAME,
 };
 
 /*

io_uring/cmd_net.c

@@ -132,6 +132,26 @@ static int io_uring_cmd_timestamp(struct socket *sock,
 	return -EAGAIN;
 }
 
+static int io_uring_cmd_getsockname(struct socket *sock,
+				    struct io_uring_cmd *cmd,
+				    unsigned int issue_flags)
+{
+	const struct io_uring_sqe *sqe = cmd->sqe;
+	struct sockaddr __user *uaddr;
+	unsigned int peer;
+	int __user *ulen;
+
+	if (sqe->ioprio || sqe->__pad1 || sqe->len || sqe->rw_flags)
+		return -EINVAL;
+
+	uaddr = u64_to_user_ptr(READ_ONCE(sqe->addr));
+	ulen = u64_to_user_ptr(sqe->addr3);
+	peer = READ_ONCE(sqe->optlen);
+	if (peer > 1)
+		return -EINVAL;
+	return do_getsockname(sock, peer, uaddr, ulen);
+}
+
 int io_uring_cmd_sock(struct io_uring_cmd *cmd, unsigned int issue_flags)
 {
 	struct socket *sock = cmd->file->private_data;
@@ -159,6 +179,8 @@ int io_uring_cmd_sock(struct io_uring_cmd *cmd, unsigned int issue_flags)
 		return io_uring_cmd_setsockopt(sock, cmd, issue_flags);
 	case SOCKET_URING_OP_TX_TIMESTAMP:
 		return io_uring_cmd_timestamp(sock, cmd, issue_flags);
+	case SOCKET_URING_OP_GETSOCKNAME:
+		return io_uring_cmd_getsockname(sock, cmd, issue_flags);
 	default:
 		return -EOPNOTSUPP;
 	}