view scpmisc.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 292f79307600
children
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/*	$OpenBSD: misc.h,v 1.12 2002/03/19 10:49:35 markus Exp $	*/

/*
 * Author: Tatu Ylonen <[email protected]>
 * Copyright (c) 1995 Tatu Ylonen <[email protected]>, Espoo, Finland
 *                    All rights reserved
 *
 * As far as I am concerned, the code I have written for this software
 * can be used freely for any purpose.  Any derived versions of this
 * software must be clearly marked as such, and if the derived work is
 * incompatible with the protocol description in the RFC file, it must be
 * called by a name other than "ssh" or "Secure Shell".
 */

char	*chop(char *);
char	*strdelim(char **);
void	 set_nonblock(int);
void	 unset_nonblock(int);
void	 set_nodelay(int);
int	 a2port(const char *);
char	*cleanhostname(char *);
char	*colon(char *);
long	 convtime(const char *);

struct passwd *pwcopy(struct passwd *);

typedef struct arglist arglist;
struct arglist {
	char    **list;
	u_int   num;
	u_int   nalloc;
};
void	 addargs(arglist *, char *, ...);
void	 replacearg(arglist *, u_int, char *, ...);
void	 freeargs(arglist *);

/* from xmalloc.h */
void	*xmalloc(size_t);
void	*xrealloc(void *, size_t);
void     xfree(void *);
char	*xstrdup(const char *);

char *ssh_get_progname(char *);
void fatal(char* fmt,...);
void sanitise_stdfd(void);

/* Required for non-BSD platforms, from OpenSSH's defines.h */
#ifndef timersub
#define timersub(a, b, result)                  \
   do {                             \
      (result)->tv_sec = (a)->tv_sec - (b)->tv_sec;     \
      (result)->tv_usec = (a)->tv_usec - (b)->tv_usec;      \
      if ((result)->tv_usec < 0) {              \
     --(result)->tv_sec;                    \
     (result)->tv_usec += 1000000;              \
      }                             \
   } while (0)
#endif

#ifndef TIMEVAL_TO_TIMESPEC
#define TIMEVAL_TO_TIMESPEC(tv, ts) {                   \
    (ts)->tv_sec = (tv)->tv_sec;                    \
    (ts)->tv_nsec = (tv)->tv_usec * 1000;               \
}
#endif