view netio.h @ 1788:1fc0012b9c38

Fix handling of replies to global requests (#112) The current code assumes that all global requests want / need a reply. This isn't always true and the request itself indicates if it wants a reply or not. It causes a specific problem with [email protected] messages. These are sent by OpenSSH after authentication to inform the client of potential other host keys for the host. This can be used to add a new type of host key or to rotate host keys. The initial information message from the server is sent as a global request, but with want_reply set to false. This means that the server doesn't expect an answer to this message. Instead the client needs to send a prove request as a reply if it wants to receive proof of ownership for the host keys. The bug doesn't cause any current problems with due to how OpenSSH treats receiving the failure message. It instead treats it as a keepalive message and further ignores it. Arguably this is a protocol violation though of Dropbear and it is only accidental that it doesn't cause a problem with OpenSSH. The bug was found when adding host keys support to libssh, which is more strict protocol wise and treats the unexpected failure message an error, also see https://gitlab.com/libssh/libssh-mirror/-/merge_requests/145 for more information. The fix here is to honor the want_reply flag in the global request and to only send a reply if the other side expects a reply.
author Dirkjan Bussink <d.bussink@gmail.com>
date Thu, 10 Dec 2020 16:13:13 +0100
parents f787f60f8e45
children 1d86a58fb52d
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#ifndef DROPBEAR_NETIO_H
#define DROPBEAR_NETIO_H

#include "includes.h"
#include "buffer.h"
#include "queue.h"

enum dropbear_prio {
	DROPBEAR_PRIO_DEFAULT = 10,
	DROPBEAR_PRIO_LOWDELAY = 11,
	DROPBEAR_PRIO_BULK = 12,
};

void set_sock_nodelay(int sock);
void set_sock_priority(int sock, enum dropbear_prio prio);

int get_sock_port(int sock);
void get_socket_address(int fd, char **local_host, char **local_port,
		char **remote_host, char **remote_port, int host_lookup);
void getaddrstring(struct sockaddr_storage* addr, 
		char **ret_host, char **ret_port, int host_lookup);
int dropbear_listen(const char* address, const char* port,
		int *socks, unsigned int sockcount, char **errstring, int *maxfd);

struct dropbear_progress_connection;

/* result is DROPBEAR_SUCCESS or DROPBEAR_FAILURE.
errstring is only set on DROPBEAR_FAILURE, returns failure message for the last attempted socket */
typedef void(*connect_callback)(int result, int sock, void* data, const char* errstring);

/* Always returns a progress connection, if it fails it will call the callback at a later point */
struct dropbear_progress_connection * connect_remote (const char* remotehost, const char* remoteport,
	connect_callback cb, void *cb_data, const char* bind_address, const char* bind_port);

/* Sets up for select() */
void set_connect_fds(fd_set *writefd);
/* Handles ready sockets after select() */
void handle_connect_fds(const fd_set *writefd);
/* Cleanup */
void remove_connect_pending(void);

/* Doesn't actually stop the connect, but adds a dummy callback instead */
void cancel_connect(struct dropbear_progress_connection *c);

void connect_set_writequeue(struct dropbear_progress_connection *c, struct Queue *writequeue);

/* TODO: writev #ifdef guard */
/* Fills out iov which contains iov_count slots, returning the number filled in iov_count */
void packet_queue_to_iovec(const struct Queue *queue, struct iovec *iov, unsigned int *iov_count);
void packet_queue_consume(struct Queue *queue, ssize_t written);

#if DROPBEAR_SERVER_TCP_FAST_OPEN
/* Try for any Linux builds, will fall back if the kernel doesn't support it */
void set_listen_fast_open(int sock);
/* Define values which may be supported by the kernel even if the libc is too old */
#ifndef TCP_FASTOPEN
#define TCP_FASTOPEN 23
#endif
#ifndef MSG_FASTOPEN
#define MSG_FASTOPEN 0x20000000
#endif
#endif

#endif