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Add some server debugging for hostbased auth.

auth_debug_add queues messages about the auth process which is sent to
the client after successful authentication.  This also sends those to
the server debug log to aid in debugging.  From bz#3507, ok djm@

/* $OpenBSD: auth-rhosts.c,v 1.57 2022/12/09 00:17:40 dtucker Exp $ */
/*
 * Author: Tatu Ylonen <ylo@cs.hut.fi>
 * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
 *                    All rights reserved
 * Rhosts authentication.  This file contains code to check whether to admit
 * the login based on rhosts authentication.  This file also processes
 * /etc/hosts.equiv.
 *
 * 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".
 */

#include <sys/types.h>
#include <sys/stat.h>

#include <errno.h>
#include <fcntl.h>
#include <netgroup.h>
#include <pwd.h>
#include <stdio.h>
#include <string.h>
#include <stdarg.h>
#include <stdlib.h>
#include <unistd.h>

#include "packet.h"
#include "uidswap.h"
#include "pathnames.h"
#include "log.h"
#include "misc.h"
#include "xmalloc.h"
#include "sshbuf.h"
#include "sshkey.h"
#include "servconf.h"
#include "canohost.h"
#include "hostfile.h"
#include "auth.h"

/* import */
extern ServerOptions options;
extern int use_privsep;

/*
 * This function processes an rhosts-style file (.rhosts, .shosts, or
 * /etc/hosts.equiv).  This returns true if authentication can be granted
 * based on the file, and returns zero otherwise.
 */

static int
check_rhosts_file(const char *filename, const char *hostname,
		  const char *ipaddr, const char *client_user,
		  const char *server_user)
{
	FILE *f;
#define RBUFLN 1024
	char buf[RBUFLN];/* Must not be larger than host, user, dummy below. */
	int fd;
	struct stat st;

	/* Open the .rhosts file, deny if unreadable */
	if ((fd = open(filename, O_RDONLY|O_NONBLOCK)) == -1)
		return 0;
	if (fstat(fd, &st) == -1) {
		close(fd);
		return 0;
	}
	if (!S_ISREG(st.st_mode)) {
		logit("User %s hosts file %s is not a regular file",
		    server_user, filename);
		close(fd);
		return 0;
	}
	unset_nonblock(fd);
	if ((f = fdopen(fd, "r")) == NULL) {
		close(fd);
		return 0;
	}
	while (fgets(buf, sizeof(buf), f)) {
		/* All three must have length >= buf to avoid overflows. */
		char hostbuf[RBUFLN], userbuf[RBUFLN], dummy[RBUFLN];
		char *host, *user, *cp;
		int negated;

		for (cp = buf; *cp == ' ' || *cp == '\t'; cp++)
			;
		if (*cp == '#' || *cp == '\n' || !*cp)
			continue;

		/*
		 * NO_PLUS is supported at least on OSF/1.  We skip it (we
		 * don't ever support the plus syntax).
		 */
		if (strncmp(cp, "NO_PLUS", 7) == 0)
			continue;

		/*
		 * This should be safe because each buffer is as big as the
		 * whole string, and thus cannot be overwritten.
		 */
		switch (sscanf(buf, "%1023s %1023s %1023s", hostbuf, userbuf,
		    dummy)) {
		case 0:
			auth_debug_add("Found empty line in %.100s.", filename);
			continue;
		case 1:
			/* Host name only. */
			strlcpy(userbuf, server_user, sizeof(userbuf));
			break;
		case 2:
			/* Got both host and user name. */
			break;
		case 3:
			auth_debug_add("Found garbage in %.100s.", filename);
			continue;
		default:
			/* Weird... */
			continue;
		}

		host = hostbuf;
		user = userbuf;
		negated = 0;

		/* Process negated host names, or positive netgroups. */
		if (host[0] == '-') {
			negated = 1;
			host++;
		} else if (host[0] == '+')
			host++;

		if (user[0] == '-') {
			negated = 1;
			user++;
		} else if (user[0] == '+')
			user++;

		/* Check for empty host/user names (particularly '+'). */
		if (!host[0] || !user[0]) {
			/* We come here if either was '+' or '-'. */
			auth_debug_add("Ignoring wild host/user names "
			    "in %.100s.", filename);
			continue;
		}
		/* Verify that host name matches. */
		if (host[0] == '@') {
			if (!innetgr(host + 1, hostname, NULL, NULL) &&
			    !innetgr(host + 1, ipaddr, NULL, NULL))
				continue;
		} else if (strcasecmp(host, hostname) &&
		    strcmp(host, ipaddr) != 0)
			continue;	/* Different hostname. */

		/* Verify that user name matches. */
		if (user[0] == '@') {
			if (!innetgr(user + 1, NULL, client_user, NULL))
				continue;
		} else if (strcmp(user, client_user) != 0)
			continue;	/* Different username. */

		/* Found the user and host. */
		fclose(f);

		/* If the entry was negated, deny access. */
		if (negated) {
			auth_debug_add("Matched negative entry in %.100s.",
			    filename);
			return 0;
		}
		/* Accept authentication. */
		return 1;
	}

	/* Authentication using this file denied. */
	fclose(f);
	return 0;
}

/*
 * Tries to authenticate the user using the .shosts or .rhosts file. Returns
 * true if authentication succeeds.  If ignore_rhosts is true, only
 * /etc/hosts.equiv will be considered (.rhosts and .shosts are ignored).
 */
int
auth_rhosts2(struct passwd *pw, const char *client_user, const char *hostname,
    const char *ipaddr)
{
	char *path = NULL;
	struct stat st;
	static const char * const rhosts_files[] = {".shosts", ".rhosts", NULL};
	u_int rhosts_file_index;
	int r;

	debug2_f("clientuser %s hostname %s ipaddr %s",
	    client_user, hostname, ipaddr);

	/* Switch to the user's uid. */
	temporarily_use_uid(pw);
	/*
	 * Quick check: if the user has no .shosts or .rhosts files and
	 * no system hosts.equiv/shosts.equiv files exist then return
	 * failure immediately without doing costly lookups from name
	 * servers.
	 */
	for (rhosts_file_index = 0; rhosts_files[rhosts_file_index];
	    rhosts_file_index++) {
		/* Check users .rhosts or .shosts. */
		xasprintf(&path, "%s/%s",
		    pw->pw_dir, rhosts_files[rhosts_file_index]);
		r = stat(path, &st);
		free(path);
		if (r >= 0)
			break;
	}
	/* Switch back to privileged uid. */
	restore_uid();

	/*
	 * Deny if The user has no .shosts or .rhosts file and there
	 * are no system-wide files.
	 */
	if (!rhosts_files[rhosts_file_index] &&
	    stat(_PATH_RHOSTS_EQUIV, &st) == -1 &&
	    stat(_PATH_SSH_HOSTS_EQUIV, &st) == -1) {
		debug3_f("no hosts access files exist");
		return 0;
	}

	/*
	 * If not logging in as superuser, try /etc/hosts.equiv and
	 * shosts.equiv.
	 */
	if (pw->pw_uid == 0)
		debug3_f("root user, ignoring system hosts files");
	else {
		if (check_rhosts_file(_PATH_RHOSTS_EQUIV, hostname, ipaddr,
		    client_user, pw->pw_name)) {
			auth_debug_add("Accepted for %.100s [%.100s] by "
			    "/etc/hosts.equiv.", hostname, ipaddr);
			return 1;
		}
		if (check_rhosts_file(_PATH_SSH_HOSTS_EQUIV, hostname, ipaddr,
		    client_user, pw->pw_name)) {
			auth_debug_add("Accepted for %.100s [%.100s] by "
			    "%.100s.", hostname, ipaddr, _PATH_SSH_HOSTS_EQUIV);
			return 1;
		}
	}

	/*
	 * Check that the home directory is owned by root or the user, and is
	 * not group or world writable.
	 */
	if (stat(pw->pw_dir, &st) == -1) {
		logit("Rhosts authentication refused for %.100s: "
		    "no home directory %.200s", pw->pw_name, pw->pw_dir);
		auth_debug_add("Rhosts authentication refused for %.100s: "
		    "no home directory %.200s", pw->pw_name, pw->pw_dir);
		return 0;
	}
	if (options.strict_modes &&
	    ((st.st_uid != 0 && st.st_uid != pw->pw_uid) ||
	    (st.st_mode & 022) != 0)) {
		logit("Rhosts authentication refused for %.100s: "
		    "bad ownership or modes for home directory.", pw->pw_name);
		auth_debug_add("Rhosts authentication refused for %.100s: "
		    "bad ownership or modes for home directory.", pw->pw_name);
		return 0;
	}
	/* Temporarily use the user's uid. */
	temporarily_use_uid(pw);

	/* Check all .rhosts files (currently .shosts and .rhosts). */
	for (rhosts_file_index = 0; rhosts_files[rhosts_file_index];
	    rhosts_file_index++) {
		/* Check users .rhosts or .shosts. */
		xasprintf(&path, "%s/%s",
		    pw->pw_dir, rhosts_files[rhosts_file_index]);
		if (stat(path, &st) == -1) {
			debug3_f("stat %s: %s", path, strerror(errno));
			free(path);
			continue;
		}

		/*
		 * Make sure that the file is either owned by the user or by
		 * root, and make sure it is not writable by anyone but the
		 * owner.  This is to help avoid novices accidentally
		 * allowing access to their account by anyone.
		 */
		if (options.strict_modes &&
		    ((st.st_uid != 0 && st.st_uid != pw->pw_uid) ||
		    (st.st_mode & 022) != 0)) {
			logit("Rhosts authentication refused for %.100s: "
			    "bad modes for %.200s", pw->pw_name, path);
			auth_debug_add("Bad file modes for %.200s", path);
			free(path);
			continue;
		}
		/*
		 * Check if we have been configured to ignore .rhosts
		 * and .shosts files.
		 */
		if (options.ignore_rhosts == IGNORE_RHOSTS_YES ||
		    (options.ignore_rhosts == IGNORE_RHOSTS_SHOSTS &&
		    strcmp(rhosts_files[rhosts_file_index], ".shosts") != 0)) {
			auth_debug_add("Server has been configured to "
			    "ignore %.100s.", rhosts_files[rhosts_file_index]);
			free(path);
			continue;
		}
		/* Check if authentication is permitted by the file. */
		if (check_rhosts_file(path, hostname, ipaddr,
		    client_user, pw->pw_name)) {
			auth_debug_add("Accepted by %.100s.",
			    rhosts_files[rhosts_file_index]);
			/* Restore the privileged uid. */
			restore_uid();
			auth_debug_add("Accepted host %s ip %s client_user "
			    "%s server_user %s", hostname, ipaddr,
			    client_user, pw->pw_name);
			free(path);
			return 1;
		}
		free(path);
	}

	/* Restore the privileged uid. */
	restore_uid();
	return 0;
}