Return to hostfile.c CVS log

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introduce hostkeys_foreach() to allow iteration over a
known_hosts file or controlled subset thereof. This will
allow us to pull out some ugly and duplicated code, and
will be used to implement hostkey rotation later.

feedback and ok markus

/* $OpenBSD: hostfile.c,v 1.60 2015/01/18 21:40:23 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 <errno.h>
#include <resolv.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <stdarg.h>

#include "xmalloc.h"
#include "match.h"
#include "sshkey.h"
#include "hostfile.h"
#include "log.h"
#include "misc.h"
#include "ssherr.h"
#include "digest.h"
#include "hmac.h"

struct hostkeys {
	struct hostkey_entry *entries;
	u_int num_entries;
};

/* XXX hmac is too easy to dictionary attack; use bcrypt? */

static int
extract_salt(const char *s, u_int l, u_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);
	free(b64salt);
	if (ret == -1) {
		debug2("extract_salt: salt decode error");
		return (-1);
	}
	if (ret != (int)ssh_hmac_bytes(SSH_DIGEST_SHA1)) {
		debug2("extract_salt: expected salt len %zd, got %d",
		    ssh_hmac_bytes(SSH_DIGEST_SHA1), ret);
		return (-1);
	}

	return (0);
}

char *
host_hash(const char *host, const char *name_from_hostfile, u_int src_len)
{
	struct ssh_hmac_ctx *ctx;
	u_char salt[256], result[256];
	char uu_salt[512], uu_result[512];
	static char encoded[1024];
	u_int i, len;

	len = ssh_digest_bytes(SSH_DIGEST_SHA1);

	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);
	}

	if ((ctx = ssh_hmac_start(SSH_DIGEST_SHA1)) == NULL ||
	    ssh_hmac_init(ctx, salt, len) < 0 ||
	    ssh_hmac_update(ctx, host, strlen(host)) < 0 ||
	    ssh_hmac_final(ctx, result, sizeof(result)))
		fatal("%s: ssh_hmac failed", __func__);
	ssh_hmac_free(ctx);

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

	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, struct sshkey *ret)
{
	char *cp;
	int r;

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

	if ((r = sshkey_read(ret, &cp)) != 0)
		return 0;

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

	/* Return results. */
	*cpp = cp;
	if (bitsp != NULL)
		*bitsp = sshkey_size(ret);
	return 1;
}

static int
hostfile_check_key(int bits, const struct sshkey *key, const char *host,
    const char *filename, u_long linenum)
{
#ifdef WITH_SSH1
	if (key == NULL || key->type != KEY_RSA1 || key->rsa == NULL)
		return 1;
	if (bits != BN_num_bits(key->rsa->n)) {
		logit("Warning: %s, line %lu: 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 %lu.",
		    bits, BN_num_bits(key->rsa->n), filename, linenum);
	}
#endif
	return 1;
}

static HostkeyMarker
check_markers(char **cpp)
{
	char marker[32], *sp, *cp = *cpp;
	int ret = MRK_NONE;

	while (*cp == '@') {
		/* Only one marker is allowed */
		if (ret != MRK_NONE)
			return MRK_ERROR;
		/* Markers are terminated by whitespace */
		if ((sp = strchr(cp, ' ')) == NULL &&
		    (sp = strchr(cp, '\t')) == NULL)
			return MRK_ERROR;
		/* Extract marker for comparison */
		if (sp <= cp + 1 || sp >= cp + sizeof(marker))
			return MRK_ERROR;
		memcpy(marker, cp, sp - cp);
		marker[sp - cp] = '\0';
		if (strcmp(marker, CA_MARKER) == 0)
			ret = MRK_CA;
		else if (strcmp(marker, REVOKE_MARKER) == 0)
			ret = MRK_REVOKE;
		else
			return MRK_ERROR;

		/* Skip past marker and any whitespace that follows it */
		cp = sp;
		for (; *cp == ' ' || *cp == '\t'; cp++)
			;
	}
	*cpp = cp;
	return ret;
}

struct hostkeys *
init_hostkeys(void)
{
	struct hostkeys *ret = xcalloc(1, sizeof(*ret));

	ret->entries = NULL;
	return ret;
}

void
load_hostkeys(struct hostkeys *hostkeys, const char *host, const char *path)
{
	FILE *f;
	char line[8192];
	u_long linenum = 0, num_loaded = 0;
	char *cp, *cp2, *hashed_host;
	HostkeyMarker marker;
	struct sshkey *key;
	u_int kbits;

	if ((f = fopen(path, "r")) == NULL)
		return;
	debug3("%s: loading entries for host \"%.100s\" from file \"%s\"",
	    __func__, host, path);
	while (read_keyfile_line(f, path, line, sizeof(line), &linenum) == 0) {
		cp = line;

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

		if ((marker = check_markers(&cp)) == MRK_ERROR) {
			verbose("%s: invalid marker at %s:%lu",
			    __func__, path, linenum);
			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 %lu of %s",
				    linenum, path);
				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 ((key = sshkey_new(KEY_UNSPEC)) == NULL) {
			error("%s: sshkey_new failed", __func__);
			break;
		}
		if (!hostfile_read_key(&cp, &kbits, key)) {
			sshkey_free(key);
#ifdef WITH_SSH1
			if ((key = sshkey_new(KEY_RSA1)) == NULL) {
				error("%s: sshkey_new failed", __func__);
				break;
			}
			if (!hostfile_read_key(&cp, &kbits, key)) {
				sshkey_free(key);
				continue;
			}
#else
			continue;
#endif
		}
		if (!hostfile_check_key(kbits, key, host, path, linenum))
			continue;

		debug3("%s: found %skey type %s in file %s:%lu", __func__,
		    marker == MRK_NONE ? "" :
		    (marker == MRK_CA ? "ca " : "revoked "),
		    sshkey_type(key), path, linenum);
		hostkeys->entries = xrealloc(hostkeys->entries,
		    hostkeys->num_entries + 1, sizeof(*hostkeys->entries));
		hostkeys->entries[hostkeys->num_entries].host = xstrdup(host);
		hostkeys->entries[hostkeys->num_entries].file = xstrdup(path);
		hostkeys->entries[hostkeys->num_entries].line = linenum;
		hostkeys->entries[hostkeys->num_entries].key = key;
		hostkeys->entries[hostkeys->num_entries].marker = marker;
		hostkeys->num_entries++;
		num_loaded++;
	}
	debug3("%s: loaded %lu keys", __func__, num_loaded);
	fclose(f);
	return;
}

void
free_hostkeys(struct hostkeys *hostkeys)
{
	u_int i;

	for (i = 0; i < hostkeys->num_entries; i++) {
		free(hostkeys->entries[i].host);
		free(hostkeys->entries[i].file);
		sshkey_free(hostkeys->entries[i].key);
		explicit_bzero(hostkeys->entries + i, sizeof(*hostkeys->entries));
	}
	free(hostkeys->entries);
	explicit_bzero(hostkeys, sizeof(*hostkeys));
	free(hostkeys);
}

static int
check_key_not_revoked(struct hostkeys *hostkeys, struct sshkey *k)
{
	int is_cert = sshkey_is_cert(k);
	u_int i;

	for (i = 0; i < hostkeys->num_entries; i++) {
		if (hostkeys->entries[i].marker != MRK_REVOKE)
			continue;
		if (sshkey_equal_public(k, hostkeys->entries[i].key))
			return -1;
		if (is_cert &&
		    sshkey_equal_public(k->cert->signature_key,
		    hostkeys->entries[i].key))
			return -1;
	}
	return 0;
}

/*
 * Match keys against a specified key, or look one up by key type.
 *
 * If looking for a keytype (key == NULL) and one is found then return
 * HOST_FOUND, otherwise HOST_NEW.
 *
 * If looking for a key (key != NULL):
 *  1. If the key is a cert and a matching CA is found, return HOST_OK
 *  2. If the key is not a cert and a matching key is found, return HOST_OK
 *  3. If no key matches but a key with a different type is found, then
 *     return HOST_CHANGED
 *  4. If no matching keys are found, then return HOST_NEW.
 *
 * Finally, check any found key is not revoked.
 */
static HostStatus
check_hostkeys_by_key_or_type(struct hostkeys *hostkeys,
    struct sshkey *k, int keytype, const struct hostkey_entry **found)
{
	u_int i;
	HostStatus end_return = HOST_NEW;
	int want_cert = sshkey_is_cert(k);
	HostkeyMarker want_marker = want_cert ? MRK_CA : MRK_NONE;
	int proto = (k ? k->type : keytype) == KEY_RSA1 ? 1 : 2;

	if (found != NULL)
		*found = NULL;

	for (i = 0; i < hostkeys->num_entries; i++) {
		if (proto == 1 && hostkeys->entries[i].key->type != KEY_RSA1)
			continue;
		if (proto == 2 && hostkeys->entries[i].key->type == KEY_RSA1)
			continue;
		if (hostkeys->entries[i].marker != want_marker)
			continue;
		if (k == NULL) {
			if (hostkeys->entries[i].key->type != keytype)
				continue;
			end_return = HOST_FOUND;
			if (found != NULL)
				*found = hostkeys->entries + i;
			k = hostkeys->entries[i].key;
			break;
		}
		if (want_cert) {
			if (sshkey_equal_public(k->cert->signature_key,
			    hostkeys->entries[i].key)) {
				/* A matching CA exists */
				end_return = HOST_OK;
				if (found != NULL)
					*found = hostkeys->entries + i;
				break;
			}
		} else {
			if (sshkey_equal(k, hostkeys->entries[i].key)) {
				end_return = HOST_OK;
				if (found != NULL)
					*found = hostkeys->entries + i;
				break;
			}
			/* A non-maching key exists */
			end_return = HOST_CHANGED;
			if (found != NULL)
				*found = hostkeys->entries + i;
		}
	}
	if (check_key_not_revoked(hostkeys, k) != 0) {
		end_return = HOST_REVOKED;
		if (found != NULL)
			*found = NULL;
	}
	return end_return;
}

HostStatus
check_key_in_hostkeys(struct hostkeys *hostkeys, struct sshkey *key,
    const struct hostkey_entry **found)
{
	if (key == NULL)
		fatal("no key to look up");
	return check_hostkeys_by_key_or_type(hostkeys, key, 0, found);
}

int
lookup_key_in_hostkeys_by_type(struct hostkeys *hostkeys, int keytype,
    const struct hostkey_entry **found)
{
	return (check_hostkeys_by_key_or_type(hostkeys, NULL, keytype,
	    found) == 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 struct sshkey *key, int store_hash)
{
	FILE *f;
	int r, 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 ((r = sshkey_write(key, f)) != 0) {
		error("%s: saving key in %s failed: %s",
		    __func__, filename, ssh_err(r));
	} else
		success = 1;
	fputc('\n', f);
	fclose(f);
	return success;
}

static int
match_maybe_hashed(const char *host, const char *names, int *was_hashed)
{
	int hashed = *names == HASH_DELIM;
	const char *hashed_host;
	size_t nlen = strlen(names);

	if (was_hashed != NULL)
		*was_hashed = hashed;
	if (hashed) {
		if ((hashed_host = host_hash(host, names, nlen)) == NULL)
			return -1;
		return nlen == strlen(hashed_host) &&
		    strncmp(hashed_host, names, nlen) == 0;
	}
	return match_hostname(host, names, nlen) == 1;
}

int
hostkeys_foreach(const char *path, hostkeys_foreach_fn *callback, void *ctx,
    const char *host, u_int options)
{
	FILE *f;
	char line[8192], oline[8192];
	u_long linenum = 0;
	char *cp, *cp2;
	u_int kbits;
	int s, r = 0;
	struct hostkey_foreach_line lineinfo;

	memset(&lineinfo, 0, sizeof(lineinfo));
	if (host == NULL && (options & HKF_WANT_MATCH_HOST) != 0)
		return SSH_ERR_INVALID_ARGUMENT;
	if ((f = fopen(path, "r")) == NULL)
		return SSH_ERR_SYSTEM_ERROR;

	debug3("%s: reading file \"%s\"", __func__, path);
	while (read_keyfile_line(f, path, line, sizeof(line), &linenum) == 0) {
		line[strcspn(line, "\n")] = '\0';
		strlcpy(oline, line, sizeof(oline));

		sshkey_free(lineinfo.key);
		memset(&lineinfo, 0, sizeof(lineinfo));
		lineinfo.path = path;
		lineinfo.linenum = linenum;
		lineinfo.line = oline;
		lineinfo.status = HKF_STATUS_OK;

		/* Skip any leading whitespace, comments and empty lines. */
		for (cp = line; *cp == ' ' || *cp == '\t'; cp++)
			;
		if (!*cp || *cp == '#' || *cp == '\n') {
			if ((options & HKF_WANT_MATCH_HOST) == 0) {
				lineinfo.status = HKF_STATUS_COMMENT;
				if ((r = callback(&lineinfo, ctx)) != 0)
					break;
			}
			continue;
		}

		if ((lineinfo.marker = check_markers(&cp)) == MRK_ERROR) {
			verbose("%s: invalid marker at %s:%lu",
			    __func__, path, linenum);
			if ((options & HKF_WANT_MATCH_HOST) == 0)
				goto bad;
			continue;
		}

		/* Find the end of the host name portion. */
		for (cp2 = cp; *cp2 && *cp2 != ' ' && *cp2 != '\t'; cp2++)
			;
		lineinfo.hosts = cp;
		*cp2++ = '\0';

		/* Check if the host name matches. */
		if (host != NULL) {
			s = match_maybe_hashed(host, lineinfo.hosts,
			    &lineinfo.was_hashed);
			if (s == 1)
				lineinfo.status = HKF_STATUS_HOST_MATCHED;
			else if ((options & HKF_WANT_MATCH_HOST) != 0)
				continue;
			else if (s == -1) {
				debug2("%s: %s:%ld: bad host hash \"%.32s\"",
				    __func__, path, linenum, lineinfo.hosts);
				goto bad;
			}
		}

		/* Got a match.  Skip host name and any following whitespace */
		for (; *cp2 == ' ' || *cp2 == '\t'; cp2++)
			;
		if (*cp2 == '\0' || *cp2 == '#') {
			debug2("%s:%ld: truncated before key", path, linenum);
			goto bad;
		}
		lineinfo.rawkey = cp = cp2;

		if ((options & HKF_WANT_PARSE_KEY) != 0) {
			/*
			 * Extract the key from the line.  This will skip
			 * any leading whitespace.  Ignore badly formatted
			 * lines.
			 */
			if ((lineinfo.key = sshkey_new(KEY_UNSPEC)) == NULL) {
				error("%s: sshkey_new failed", __func__);
				return SSH_ERR_ALLOC_FAIL;
			}
			if (!hostfile_read_key(&cp, &kbits, lineinfo.key)) {
#ifdef WITH_SSH1
				sshkey_free(lineinfo.key);
				lineinfo.key = sshkey_new(KEY_RSA1);
				if (lineinfo.key  == NULL) {
					error("%s: sshkey_new fail", __func__);
					return SSH_ERR_ALLOC_FAIL;
				}
				if (!hostfile_read_key(&cp, &kbits,
				    lineinfo.key))
					goto bad;
#else
				goto bad;
#endif
			}
			if (!hostfile_check_key(kbits, lineinfo.key, host,
			    path, linenum)) {
 bad:
				lineinfo.status = HKF_STATUS_INVALID;
				if ((r = callback(&lineinfo, ctx)) != 0)
					break;
				continue;
			}
		}
		if ((r = callback(&lineinfo, ctx)) != 0)
			break;
	}
	sshkey_free(lineinfo.key);
	fclose(f);
	return r;
}