Return to hostfile.c CVS log

Up to [local] / src / usr.bin / ssh

Add support for certificate key types for users and hosts.

OpenSSH certificate key types are not X.509 certificates, but a much
simpler format that encodes a public key, identity information and
some validity constraints and signs it with a CA key. CA keys are
regular SSH keys. This certificate style avoids the attack surface
of X.509 certificates and is very easy to deploy.

Certified host keys allow automatic acceptance of new host keys
when a CA certificate is marked as trusted in ~/.ssh/known_hosts.
see VERIFYING HOST KEYS in ssh(1) for details.

Certified user keys allow authentication of users when the signing
CA key is marked as trusted in authorized_keys. See "AUTHORIZED_KEYS
FILE FORMAT" in sshd(8) for details.

Certificates are minted using ssh-keygen(1), documentation is in
the "CERTIFICATES" section of that manpage.

Documentation on the format of certificates is in the file
PROTOCOL.certkeys

feedback and ok markus@

/* $OpenBSD: hostfile.c,v 1.47 2010/02/26 20:29:54 djm Exp $ */
/*
 * Author: Tatu Ylonen <ylo@cs.hut.fi>
 * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
 *                    All rights reserved
 * Functions for manipulating the known hosts files.
 *
 * 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".
 *
 *
 * Copyright (c) 1999, 2000 Markus Friedl.  All rights reserved.
 * Copyright (c) 1999 Niels Provos.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#include <sys/types.h>

#include <netinet/in.h>

#include <openssl/hmac.h>
#include <openssl/sha.h>

#include <resolv.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#include "xmalloc.h"
#include "match.h"
#include "key.h"
#include "hostfile.h"
#include "log.h"

static int
extract_salt(const char *s, u_int l, char *salt, size_t salt_len)
{
	char *p, *b64salt;
	u_int b64len;
	int ret;

	if (l < sizeof(HASH_MAGIC) - 1) {
		debug2("extract_salt: string too short");
		return (-1);
	}
	if (strncmp(s, HASH_MAGIC, sizeof(HASH_MAGIC) - 1) != 0) {
		debug2("extract_salt: invalid magic identifier");
		return (-1);
	}
	s += sizeof(HASH_MAGIC) - 1;
	l -= sizeof(HASH_MAGIC) - 1;
	if ((p = memchr(s, HASH_DELIM, l)) == NULL) {
		debug2("extract_salt: missing salt termination character");
		return (-1);
	}

	b64len = p - s;
	/* Sanity check */
	if (b64len == 0 || b64len > 1024) {
		debug2("extract_salt: bad encoded salt length %u", b64len);
		return (-1);
	}
	b64salt = xmalloc(1 + b64len);
	memcpy(b64salt, s, b64len);
	b64salt[b64len] = '\0';

	ret = __b64_pton(b64salt, salt, salt_len);
	xfree(b64salt);
	if (ret == -1) {
		debug2("extract_salt: salt decode error");
		return (-1);
	}
	if (ret != SHA_DIGEST_LENGTH) {
		debug2("extract_salt: expected salt len %d, got %d",
		    SHA_DIGEST_LENGTH, ret);
		return (-1);
	}

	return (0);
}

char *
host_hash(const char *host, const char *name_from_hostfile, u_int src_len)
{
	const EVP_MD *md = EVP_sha1();
	HMAC_CTX mac_ctx;
	char salt[256], result[256], uu_salt[512], uu_result[512];
	static char encoded[1024];
	u_int i, len;

	len = EVP_MD_size(md);

	if (name_from_hostfile == NULL) {
		/* Create new salt */
		for (i = 0; i < len; i++)
			salt[i] = arc4random();
	} else {
		/* Extract salt from known host entry */
		if (extract_salt(name_from_hostfile, src_len, salt,
		    sizeof(salt)) == -1)
			return (NULL);
	}

	HMAC_Init(&mac_ctx, salt, len, md);
	HMAC_Update(&mac_ctx, host, strlen(host));
	HMAC_Final(&mac_ctx, result, NULL);
	HMAC_cleanup(&mac_ctx);

	if (__b64_ntop(salt, len, uu_salt, sizeof(uu_salt)) == -1 ||
	    __b64_ntop(result, len, uu_result, sizeof(uu_result)) == -1)
		fatal("host_hash: __b64_ntop failed");

	snprintf(encoded, sizeof(encoded), "%s%s%c%s", HASH_MAGIC, uu_salt,
	    HASH_DELIM, uu_result);

	return (encoded);
}

/*
 * Parses an RSA (number of bits, e, n) or DSA key from a string.  Moves the
 * pointer over the key.  Skips any whitespace at the beginning and at end.
 */

int
hostfile_read_key(char **cpp, u_int *bitsp, Key *ret)
{
	char *cp;

	/* Skip leading whitespace. */
	for (cp = *cpp; *cp == ' ' || *cp == '\t'; cp++)
		;

	if (key_read(ret, &cp) != 1)
		return 0;

	/* Skip trailing whitespace. */
	for (; *cp == ' ' || *cp == '\t'; cp++)
		;

	/* Return results. */
	*cpp = cp;
	*bitsp = key_size(ret);
	return 1;
}

static int
hostfile_check_key(int bits, const Key *key, const char *host, const char *filename, int linenum)
{
	if (key == NULL || key->type != KEY_RSA1 || key->rsa == NULL)
		return 1;
	if (bits != BN_num_bits(key->rsa->n)) {
		logit("Warning: %s, line %d: keysize mismatch for host %s: "
		    "actual %d vs. announced %d.",
		    filename, linenum, host, BN_num_bits(key->rsa->n), bits);
		logit("Warning: replace %d with %d in %s, line %d.",
		    bits, BN_num_bits(key->rsa->n), filename, linenum);
	}
	return 1;
}

/*
 * Checks whether the given host (which must be in all lowercase) is already
 * in the list of our known hosts. Returns HOST_OK if the host is known and
 * has the specified key, HOST_NEW if the host is not known, and HOST_CHANGED
 * if the host is known but used to have a different host key.
 *
 * If no 'key' has been specified and a key of type 'keytype' is known
 * for the specified host, then HOST_FOUND is returned.
 */

static HostStatus
check_host_in_hostfile_by_key_or_type(const char *filename,
    const char *host, const Key *key, int keytype, Key *found, int *numret)
{
	FILE *f;
	char line[8192];
	int linenum = 0, want_cert = key_is_cert(key);
	u_int kbits;
	char *cp, *cp2, *hashed_host;
	HostStatus end_return;

	debug3("check_host_in_hostfile: host %s filename %s", host, filename);

	/* Open the file containing the list of known hosts. */
	f = fopen(filename, "r");
	if (!f)
		return HOST_NEW;

	/*
	 * Return value when the loop terminates.  This is set to
	 * HOST_CHANGED if we have seen a different key for the host and have
	 * not found the proper one.
	 */
	end_return = HOST_NEW;

	/* Go through the file. */
	while (fgets(line, sizeof(line), f)) {
		cp = line;
		linenum++;

		/* Skip any leading whitespace, comments and empty lines. */
		for (; *cp == ' ' || *cp == '\t'; cp++)
			;
		if (!*cp || *cp == '#' || *cp == '\n')
			continue;

		/*
		 * Ignore CA keys when looking for raw keys.
		 * Ignore raw keys when looking for CA keys.
		 */
		if (strncasecmp(cp, CA_MARKER, sizeof(CA_MARKER) - 1) == 0 &&
		    (cp[sizeof(CA_MARKER) - 1] == ' ' ||
		    cp[sizeof(CA_MARKER) - 1] == '\t')) {
			if (want_cert) {
				/* Skip the marker and following whitespace */
				cp += sizeof(CA_MARKER);
				for (; *cp == ' ' || *cp == '\t'; cp++)
					;
			} else
				continue;
		} else if (want_cert)
			continue;

		/* Find the end of the host name portion. */
		for (cp2 = cp; *cp2 && *cp2 != ' ' && *cp2 != '\t'; cp2++)
			;

		/* Check if the host name matches. */
		if (match_hostname(host, cp, (u_int) (cp2 - cp)) != 1) {
			if (*cp != HASH_DELIM)
				continue;
			hashed_host = host_hash(host, cp, (u_int) (cp2 - cp));
			if (hashed_host == NULL) {
				debug("Invalid hashed host line %d of %s",
				    linenum, filename);
				continue;
			}
			if (strncmp(hashed_host, cp, (u_int) (cp2 - cp)) != 0)
				continue;
		}

		/* Got a match.  Skip host name. */
		cp = cp2;

		/*
		 * Extract the key from the line.  This will skip any leading
		 * whitespace.  Ignore badly formatted lines.
		 */
		if (!hostfile_read_key(&cp, &kbits, found))
			continue;

		if (numret != NULL)
			*numret = linenum;

		if (key == NULL) {
			/* we found a key of the requested type */
			if (found->type == keytype) {
				fclose(f);
				return HOST_FOUND;
			}
			continue;
		}

		if (!hostfile_check_key(kbits, found, host, filename, linenum))
			continue;

		/* Check if the current key is the same as the given key. */
		if (want_cert && key_equal(key->cert->signature_key, found)) {
			/* Found CA cert for key */
			debug3("check_host_in_hostfile: CA match line %d",
			    linenum);
			fclose(f);
			return HOST_OK;
		} else if (!want_cert && key_equal(key, found)) {
			/* Found identical key */
			debug3("check_host_in_hostfile: match line %d", linenum);
			fclose(f);
			return HOST_OK;
		}
		/*
		 * They do not match.  We will continue to go through the
		 * file; however, we note that we will not return that it is
		 * new.
		 */
		end_return = HOST_CHANGED;
	}
	/* Clear variables and close the file. */
	fclose(f);

	/*
	 * Return either HOST_NEW or HOST_CHANGED, depending on whether we
	 * saw a different key for the host.
	 */
	return end_return;
}

HostStatus
check_host_in_hostfile(const char *filename, const char *host, const Key *key,
    Key *found, int *numret)
{
	if (key == NULL)
		fatal("no key to look up");
	return (check_host_in_hostfile_by_key_or_type(filename, host, key, 0,
	    found, numret));
}

int
lookup_key_in_hostfile_by_type(const char *filename, const char *host,
    int keytype, Key *found, int *numret)
{
	return (check_host_in_hostfile_by_key_or_type(filename, host, NULL,
	    keytype, found, numret) == HOST_FOUND);
}

/*
 * Appends an entry to the host file.  Returns false if the entry could not
 * be appended.
 */

int
add_host_to_hostfile(const char *filename, const char *host, const Key *key,
    int store_hash)
{
	FILE *f;
	int success = 0;
	char *hashed_host = NULL;

	if (key == NULL)
		return 1;	/* XXX ? */
	f = fopen(filename, "a");
	if (!f)
		return 0;

	if (store_hash) {
		if ((hashed_host = host_hash(host, NULL, 0)) == NULL) {
			error("add_host_to_hostfile: host_hash failed");
			fclose(f);
			return 0;
		}
	}
	fprintf(f, "%s ", store_hash ? hashed_host : host);

	if (key_write(key, f)) {
		success = 1;
	} else {
		error("add_host_to_hostfile: saving key in %s failed", filename);
	}
	fprintf(f, "\n");
	fclose(f);
	return success;
}