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openssh/auth-options.c

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/* $OpenBSD: auth-options.c,v 1.74 2017/09/12 06:32:07 djm Exp $ */
/*
* Author: Tatu Ylonen <ylo@cs.hut.fi>
* Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, 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".
*/
#include "includes.h"
#include <sys/types.h>
#include <netdb.h>
#include <pwd.h>
#include <string.h>
#include <stdio.h>
#include <stdarg.h>
#include "openbsd-compat/sys-queue.h"
#include "key.h" /* XXX for typedef */
#include "buffer.h" /* XXX for typedef */
#include "xmalloc.h"
#include "match.h"
#include "ssherr.h"
#include "log.h"
#include "canohost.h"
#include "packet.h"
#include "sshbuf.h"
#include "misc.h"
#include "channels.h"
#include "servconf.h"
#include "sshkey.h"
#include "auth-options.h"
#include "hostfile.h"
#include "auth.h"
/* Flags set authorized_keys flags */
int no_port_forwarding_flag = 0;
int no_agent_forwarding_flag = 0;
int no_x11_forwarding_flag = 0;
int no_pty_flag = 0;
int no_user_rc = 0;
int key_is_cert_authority = 0;
/* "command=" option. */
char *forced_command = NULL;
/* "environment=" options. */
struct envstring *custom_environment = NULL;
/* "tunnel=" option. */
int forced_tun_device = -1;
/* "principals=" option. */
char *authorized_principals = NULL;
extern ServerOptions options;
/* XXX refactor to be stateless */
void
auth_clear_options(void)
{
struct ssh *ssh = active_state; /* XXX */
no_agent_forwarding_flag = 0;
no_port_forwarding_flag = 0;
no_pty_flag = 0;
no_x11_forwarding_flag = 0;
no_user_rc = 0;
key_is_cert_authority = 0;
while (custom_environment) {
struct envstring *ce = custom_environment;
custom_environment = ce->next;
free(ce->s);
free(ce);
}
free(forced_command);
forced_command = NULL;
free(authorized_principals);
authorized_principals = NULL;
forced_tun_device = -1;
channel_clear_permitted_opens(ssh);
}
/*
* Match flag 'opt' in *optsp, and if allow_negate is set then also match
* 'no-opt'. Returns -1 if option not matched, 1 if option matches or 0
* if negated option matches.
* If the option or negated option matches, then *optsp is updated to
* point to the first character after the option and, if 'msg' is not NULL
* then a message based on it added via auth_debug_add().
*/
static int
match_flag(const char *opt, int allow_negate, char **optsp, const char *msg)
{
size_t opt_len = strlen(opt);
char *opts = *optsp;
int negate = 0;
if (allow_negate && strncasecmp(opts, "no-", 3) == 0) {
opts += 3;
negate = 1;
}
if (strncasecmp(opts, opt, opt_len) == 0) {
*optsp = opts + opt_len;
if (msg != NULL) {
auth_debug_add("%s %s.", msg,
negate ? "disabled" : "enabled");
}
return negate ? 0 : 1;
}
return -1;
}
/*
* return 1 if access is granted, 0 if not.
* side effect: sets key option flags
* XXX remove side effects; fill structure instead.
*/
int
auth_parse_options(struct passwd *pw, char *opts, const char *file,
u_long linenum)
{
struct ssh *ssh = active_state; /* XXX */
const char *cp;
int i, r;
/* reset options */
auth_clear_options();
if (!opts)
return 1;
while (*opts && *opts != ' ' && *opts != '\t') {
if ((r = match_flag("cert-authority", 0, &opts, NULL)) != -1) {
key_is_cert_authority = r;
goto next_option;
}
if ((r = match_flag("restrict", 0, &opts, NULL)) != -1) {
auth_debug_add("Key is restricted.");
no_port_forwarding_flag = 1;
no_agent_forwarding_flag = 1;
no_x11_forwarding_flag = 1;
no_pty_flag = 1;
no_user_rc = 1;
goto next_option;
}
if ((r = match_flag("port-forwarding", 1, &opts,
"Port forwarding")) != -1) {
no_port_forwarding_flag = r != 1;
goto next_option;
}
if ((r = match_flag("agent-forwarding", 1, &opts,
"Agent forwarding")) != -1) {
no_agent_forwarding_flag = r != 1;
goto next_option;
}
if ((r = match_flag("x11-forwarding", 1, &opts,
"X11 forwarding")) != -1) {
no_x11_forwarding_flag = r != 1;
goto next_option;
}
if ((r = match_flag("pty", 1, &opts,
"PTY allocation")) != -1) {
no_pty_flag = r != 1;
goto next_option;
}
if ((r = match_flag("user-rc", 1, &opts,
"User rc execution")) != -1) {
no_user_rc = r != 1;
goto next_option;
}
cp = "command=\"";
if (strncasecmp(opts, cp, strlen(cp)) == 0) {
opts += strlen(cp);
free(forced_command);
forced_command = xmalloc(strlen(opts) + 1);
i = 0;
while (*opts) {
if (*opts == '"')
break;
if (*opts == '\\' && opts[1] == '"') {
opts += 2;
forced_command[i++] = '"';
continue;
}
forced_command[i++] = *opts++;
}
if (!*opts) {
debug("%.100s, line %lu: missing end quote",
file, linenum);
auth_debug_add("%.100s, line %lu: missing end quote",
file, linenum);
free(forced_command);
forced_command = NULL;
goto bad_option;
}
forced_command[i] = '\0';
auth_debug_add("Forced command.");
opts++;
goto next_option;
}
cp = "principals=\"";
if (strncasecmp(opts, cp, strlen(cp)) == 0) {
opts += strlen(cp);
free(authorized_principals);
authorized_principals = xmalloc(strlen(opts) + 1);
i = 0;
while (*opts) {
if (*opts == '"')
break;
if (*opts == '\\' && opts[1] == '"') {
opts += 2;
authorized_principals[i++] = '"';
continue;
}
authorized_principals[i++] = *opts++;
}
if (!*opts) {
debug("%.100s, line %lu: missing end quote",
file, linenum);
auth_debug_add("%.100s, line %lu: missing end quote",
file, linenum);
free(authorized_principals);
authorized_principals = NULL;
goto bad_option;
}
authorized_principals[i] = '\0';
auth_debug_add("principals: %.900s",
authorized_principals);
opts++;
goto next_option;
}
cp = "environment=\"";
if (strncasecmp(opts, cp, strlen(cp)) == 0) {
char *s;
struct envstring *new_envstring;
opts += strlen(cp);
s = xmalloc(strlen(opts) + 1);
i = 0;
while (*opts) {
if (*opts == '"')
break;
if (*opts == '\\' && opts[1] == '"') {
opts += 2;
s[i++] = '"';
continue;
}
s[i++] = *opts++;
}
if (!*opts) {
debug("%.100s, line %lu: missing end quote",
file, linenum);
auth_debug_add("%.100s, line %lu: missing end quote",
file, linenum);
free(s);
goto bad_option;
}
s[i] = '\0';
opts++;
if (options.permit_user_env) {
auth_debug_add("Adding to environment: "
"%.900s", s);
debug("Adding to environment: %.900s", s);
new_envstring = xcalloc(1,
sizeof(*new_envstring));
new_envstring->s = s;
new_envstring->next = custom_environment;
custom_environment = new_envstring;
s = NULL;
}
free(s);
goto next_option;
}
cp = "from=\"";
if (strncasecmp(opts, cp, strlen(cp)) == 0) {
const char *remote_ip = ssh_remote_ipaddr(ssh);
const char *remote_host = auth_get_canonical_hostname(
ssh, options.use_dns);
char *patterns = xmalloc(strlen(opts) + 1);
opts += strlen(cp);
i = 0;
while (*opts) {
if (*opts == '"')
break;
if (*opts == '\\' && opts[1] == '"') {
opts += 2;
patterns[i++] = '"';
continue;
}
patterns[i++] = *opts++;
}
if (!*opts) {
debug("%.100s, line %lu: missing end quote",
file, linenum);
auth_debug_add("%.100s, line %lu: missing end quote",
file, linenum);
free(patterns);
goto bad_option;
}
patterns[i] = '\0';
opts++;
switch (match_host_and_ip(remote_host, remote_ip,
patterns)) {
case 1:
free(patterns);
/* Host name matches. */
goto next_option;
case -1:
debug("%.100s, line %lu: invalid criteria",
file, linenum);
auth_debug_add("%.100s, line %lu: "
"invalid criteria", file, linenum);
/* FALLTHROUGH */
case 0:
free(patterns);
logit("Authentication tried for %.100s with "
"correct key but not from a permitted "
"host (host=%.200s, ip=%.200s).",
pw->pw_name, remote_host, remote_ip);
auth_debug_add("Your host '%.200s' is not "
"permitted to use this key for login.",
remote_host);
break;
}
/* deny access */
return 0;
}
cp = "permitopen=\"";
if (strncasecmp(opts, cp, strlen(cp)) == 0) {
char *host, *p;
int port;
char *patterns = xmalloc(strlen(opts) + 1);
opts += strlen(cp);
i = 0;
while (*opts) {
if (*opts == '"')
break;
if (*opts == '\\' && opts[1] == '"') {
opts += 2;
patterns[i++] = '"';
continue;
}
patterns[i++] = *opts++;
}
if (!*opts) {
debug("%.100s, line %lu: missing end quote",
file, linenum);
auth_debug_add("%.100s, line %lu: missing "
"end quote", file, linenum);
free(patterns);
goto bad_option;
}
patterns[i] = '\0';
opts++;
p = patterns;
/* XXX - add streamlocal support */
host = hpdelim(&p);
if (host == NULL || strlen(host) >= NI_MAXHOST) {
debug("%.100s, line %lu: Bad permitopen "
"specification <%.100s>", file, linenum,
patterns);
auth_debug_add("%.100s, line %lu: "
"Bad permitopen specification", file,
linenum);
free(patterns);
goto bad_option;
}
host = cleanhostname(host);
if (p == NULL || (port = permitopen_port(p)) < 0) {
debug("%.100s, line %lu: Bad permitopen port "
"<%.100s>", file, linenum, p ? p : "");
auth_debug_add("%.100s, line %lu: "
"Bad permitopen port", file, linenum);
free(patterns);
goto bad_option;
}
if ((options.allow_tcp_forwarding & FORWARD_LOCAL) != 0)
channel_add_permitted_opens(ssh, host, port);
free(patterns);
goto next_option;
}
cp = "tunnel=\"";
if (strncasecmp(opts, cp, strlen(cp)) == 0) {
char *tun = NULL;
opts += strlen(cp);
tun = xmalloc(strlen(opts) + 1);
i = 0;
while (*opts) {
if (*opts == '"')
break;
tun[i++] = *opts++;
}
if (!*opts) {
debug("%.100s, line %lu: missing end quote",
file, linenum);
auth_debug_add("%.100s, line %lu: missing end quote",
file, linenum);
free(tun);
forced_tun_device = -1;
goto bad_option;
}
tun[i] = '\0';
forced_tun_device = a2tun(tun, NULL);
free(tun);
if (forced_tun_device == SSH_TUNID_ERR) {
debug("%.100s, line %lu: invalid tun device",
file, linenum);
auth_debug_add("%.100s, line %lu: invalid tun device",
file, linenum);
forced_tun_device = -1;
goto bad_option;
}
auth_debug_add("Forced tun device: %d", forced_tun_device);
opts++;
goto next_option;
}
next_option:
/*
* Skip the comma, and move to the next option
* (or break out if there are no more).
*/
if (!*opts)
fatal("Bugs in auth-options.c option processing.");
if (*opts == ' ' || *opts == '\t')
break; /* End of options. */
if (*opts != ',')
goto bad_option;
opts++;
/* Process the next option. */
}
/* grant access */
return 1;
bad_option:
logit("Bad options in %.100s file, line %lu: %.50s",
file, linenum, opts);
auth_debug_add("Bad options in %.100s file, line %lu: %.50s",
file, linenum, opts);
/* deny access */
return 0;
}
#define OPTIONS_CRITICAL 1
#define OPTIONS_EXTENSIONS 2
static int
parse_option_list(struct sshbuf *oblob, struct passwd *pw,
u_int which, int crit,
int *cert_no_port_forwarding_flag,
int *cert_no_agent_forwarding_flag,
int *cert_no_x11_forwarding_flag,
int *cert_no_pty_flag,
int *cert_no_user_rc,
char **cert_forced_command,
int *cert_source_address_done)
{
struct ssh *ssh = active_state; /* XXX */
char *command, *allowed;
const char *remote_ip;
char *name = NULL;
struct sshbuf *c = NULL, *data = NULL;
int r, ret = -1, result, found;
if ((c = sshbuf_fromb(oblob)) == NULL) {
error("%s: sshbuf_fromb failed", __func__);
goto out;
}
while (sshbuf_len(c) > 0) {
sshbuf_free(data);
data = NULL;
if ((r = sshbuf_get_cstring(c, &name, NULL)) != 0 ||
(r = sshbuf_froms(c, &data)) != 0) {
error("Unable to parse certificate options: %s",
ssh_err(r));
goto out;
}
debug3("found certificate option \"%.100s\" len %zu",
name, sshbuf_len(data));
found = 0;
if ((which & OPTIONS_EXTENSIONS) != 0) {
if (strcmp(name, "permit-X11-forwarding") == 0) {
*cert_no_x11_forwarding_flag = 0;
found = 1;
} else if (strcmp(name,
"permit-agent-forwarding") == 0) {
*cert_no_agent_forwarding_flag = 0;
found = 1;
} else if (strcmp(name,
"permit-port-forwarding") == 0) {
*cert_no_port_forwarding_flag = 0;
found = 1;
} else if (strcmp(name, "permit-pty") == 0) {
*cert_no_pty_flag = 0;
found = 1;
} else if (strcmp(name, "permit-user-rc") == 0) {
*cert_no_user_rc = 0;
found = 1;
}
}
if (!found && (which & OPTIONS_CRITICAL) != 0) {
if (strcmp(name, "force-command") == 0) {
if ((r = sshbuf_get_cstring(data, &command,
NULL)) != 0) {
error("Unable to parse \"%s\" "
"section: %s", name, ssh_err(r));
goto out;
}
if (*cert_forced_command != NULL) {
error("Certificate has multiple "
"force-command options");
free(command);
goto out;
}
*cert_forced_command = command;
found = 1;
}
if (strcmp(name, "source-address") == 0) {
if ((r = sshbuf_get_cstring(data, &allowed,
NULL)) != 0) {
error("Unable to parse \"%s\" "
"section: %s", name, ssh_err(r));
goto out;
}
if ((*cert_source_address_done)++) {
error("Certificate has multiple "
"source-address options");
free(allowed);
goto out;
}
remote_ip = ssh_remote_ipaddr(ssh);
result = addr_match_cidr_list(remote_ip,
allowed);
free(allowed);
switch (result) {
case 1:
/* accepted */
break;
case 0:
/* no match */
logit("Authentication tried for %.100s "
"with valid certificate but not "
"from a permitted host "
"(ip=%.200s).", pw->pw_name,
remote_ip);
auth_debug_add("Your address '%.200s' "
"is not permitted to use this "
"certificate for login.",
remote_ip);
goto out;
case -1:
default:
error("Certificate source-address "
"contents invalid");
goto out;
}
found = 1;
}
}
if (!found) {
if (crit) {
error("Certificate critical option \"%s\" "
"is not supported", name);
goto out;
} else {
logit("Certificate extension \"%s\" "
"is not supported", name);
}
} else if (sshbuf_len(data) != 0) {
error("Certificate option \"%s\" corrupt "
"(extra data)", name);
goto out;
}
free(name);
name = NULL;
}
/* successfully parsed all options */
ret = 0;
out:
if (ret != 0 &&
cert_forced_command != NULL &&
*cert_forced_command != NULL) {
free(*cert_forced_command);
*cert_forced_command = NULL;
}
free(name);
sshbuf_free(data);
sshbuf_free(c);
return ret;
}
/*
* Set options from critical certificate options. These supersede user key
* options so this must be called after auth_parse_options().
*/
int
auth_cert_options(struct sshkey *k, struct passwd *pw, const char **reason)
{
int cert_no_port_forwarding_flag = 1;
int cert_no_agent_forwarding_flag = 1;
int cert_no_x11_forwarding_flag = 1;
int cert_no_pty_flag = 1;
int cert_no_user_rc = 1;
char *cert_forced_command = NULL;
int cert_source_address_done = 0;
*reason = "invalid certificate options";
/* Separate options and extensions for v01 certs */
if (parse_option_list(k->cert->critical, pw,
OPTIONS_CRITICAL, 1, NULL, NULL, NULL, NULL, NULL,
&cert_forced_command,
&cert_source_address_done) == -1)
return -1;
if (parse_option_list(k->cert->extensions, pw,
OPTIONS_EXTENSIONS, 0,
&cert_no_port_forwarding_flag,
&cert_no_agent_forwarding_flag,
&cert_no_x11_forwarding_flag,
&cert_no_pty_flag,
&cert_no_user_rc,
NULL, NULL) == -1)
return -1;
no_port_forwarding_flag |= cert_no_port_forwarding_flag;
no_agent_forwarding_flag |= cert_no_agent_forwarding_flag;
no_x11_forwarding_flag |= cert_no_x11_forwarding_flag;
no_pty_flag |= cert_no_pty_flag;
no_user_rc |= cert_no_user_rc;
/*
* Only permit both CA and key option forced-command if they match.
* Otherwise refuse the certificate.
*/
if (cert_forced_command != NULL && forced_command != NULL) {
if (strcmp(forced_command, cert_forced_command) == 0) {
free(forced_command);
forced_command = cert_forced_command;
} else {
*reason = "certificate and key options forced command "
"do not match";
free(cert_forced_command);
return -1;
}
} else if (cert_forced_command != NULL)
forced_command = cert_forced_command;
/* success */
*reason = NULL;
return 0;
}
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