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openssh/auth-options.c
Damien Miller da108ece68 - djm@cvs.openbsd.org 2010/08/31 09:58:37 
[auth-options.c auth1.c auth2.c bufaux.c buffer.h kex.c key.c packet.c]
     [packet.h ssh-dss.c ssh-rsa.c]
     Add buffer_get_cstring() and related functions that verify that the
     string extracted from the buffer contains no embedded \0 characters*
     This prevents random (possibly malicious) crap from being appended to
     strings where it would not be noticed if the string is used with
     a string(3) function.

     Use the new API in a few sensitive places.

     * actually, we allow a single one at the end of the string for now because
     we don't know how many deployed implementations get this wrong, but don't
     count on this to remain indefinitely.
2010-08-31 22:36:39 +10:00

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/* $OpenBSD: auth-options.c,v 1.53 2010/08/31 09:58:37 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 "xmalloc.h"
#include "match.h"
#include "log.h"
#include "canohost.h"
#include "buffer.h"
#include "channels.h"
#include "servconf.h"
#include "misc.h"
#include "key.h"
#include "auth-options.h"
#include "hostfile.h"
#include "auth.h"
#ifdef GSSAPI
#include "ssh-gss.h"
#endif
#include "monitor_wrap.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;
void
auth_clear_options(void)
{
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;
xfree(ce->s);
xfree(ce);
}
if (forced_command) {
xfree(forced_command);
forced_command = NULL;
}
if (authorized_principals) {
xfree(authorized_principals);
authorized_principals = NULL;
}
forced_tun_device = -1;
channel_clear_permitted_opens();
}
/*
* return 1 if access is granted, 0 if not.
* side effect: sets key option flags
*/
int
auth_parse_options(struct passwd *pw, char *opts, char *file, u_long linenum)
{
const char *cp;
int i;
/* reset options */
auth_clear_options();
if (!opts)
return 1;
while (*opts && *opts != ' ' && *opts != '\t') {
cp = "cert-authority";
if (strncasecmp(opts, cp, strlen(cp)) == 0) {
key_is_cert_authority = 1;
opts += strlen(cp);
goto next_option;
}
cp = "no-port-forwarding";
if (strncasecmp(opts, cp, strlen(cp)) == 0) {
auth_debug_add("Port forwarding disabled.");
no_port_forwarding_flag = 1;
opts += strlen(cp);
goto next_option;
}
cp = "no-agent-forwarding";
if (strncasecmp(opts, cp, strlen(cp)) == 0) {
auth_debug_add("Agent forwarding disabled.");
no_agent_forwarding_flag = 1;
opts += strlen(cp);
goto next_option;
}
cp = "no-X11-forwarding";
if (strncasecmp(opts, cp, strlen(cp)) == 0) {
auth_debug_add("X11 forwarding disabled.");
no_x11_forwarding_flag = 1;
opts += strlen(cp);
goto next_option;
}
cp = "no-pty";
if (strncasecmp(opts, cp, strlen(cp)) == 0) {
auth_debug_add("Pty allocation disabled.");
no_pty_flag = 1;
opts += strlen(cp);
goto next_option;
}
cp = "no-user-rc";
if (strncasecmp(opts, cp, strlen(cp)) == 0) {
auth_debug_add("User rc file execution disabled.");
no_user_rc = 1;
opts += strlen(cp);
goto next_option;
}
cp = "command=\"";
if (strncasecmp(opts, cp, strlen(cp)) == 0) {
opts += strlen(cp);
if (forced_command != NULL)
xfree(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);
xfree(forced_command);
forced_command = NULL;
goto bad_option;
}
forced_command[i] = '\0';
auth_debug_add("Forced command: %.900s", forced_command);
opts++;
goto next_option;
}
cp = "principals=\"";
if (strncasecmp(opts, cp, strlen(cp)) == 0) {
opts += strlen(cp);
if (authorized_principals != NULL)
xfree(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);
xfree(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 (options.permit_user_env &&
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);
xfree(s);
goto bad_option;
}
s[i] = '\0';
auth_debug_add("Adding to environment: %.900s", s);
debug("Adding to environment: %.900s", s);
opts++;
new_envstring = xmalloc(sizeof(struct envstring));
new_envstring->s = s;
new_envstring->next = custom_environment;
custom_environment = new_envstring;
goto next_option;
}
cp = "from=\"";
if (strncasecmp(opts, cp, strlen(cp)) == 0) {
const char *remote_ip = get_remote_ipaddr();
const char *remote_host = get_canonical_hostname(
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);
xfree(patterns);
goto bad_option;
}
patterns[i] = '\0';
opts++;
switch (match_host_and_ip(remote_host, remote_ip,
patterns)) {
case 1:
xfree(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:
xfree(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);
xfree(patterns);
goto bad_option;
}
patterns[i] = '\0';
opts++;
p = patterns;
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);
xfree(patterns);
goto bad_option;
}
host = cleanhostname(host);
if (p == NULL || (port = a2port(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);
xfree(patterns);
goto bad_option;
}
if (options.allow_tcp_forwarding)
channel_add_permitted_opens(host, port);
xfree(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);
xfree(tun);
forced_tun_device = -1;
goto bad_option;
}
tun[i] = '\0';
forced_tun_device = a2tun(tun, NULL);
xfree(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(u_char *optblob, size_t optblob_len, 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)
{
char *command, *allowed;
const char *remote_ip;
u_char *name = NULL, *data_blob = NULL;
u_int nlen, dlen, clen;
Buffer c, data;
int ret = -1, found;
buffer_init(&data);
/* Make copy to avoid altering original */
buffer_init(&c);
buffer_append(&c, optblob, optblob_len);
while (buffer_len(&c) > 0) {
if ((name = buffer_get_cstring_ret(&c, &nlen)) == NULL ||
(data_blob = buffer_get_string_ret(&c, &dlen)) == NULL) {
error("Certificate options corrupt");
goto out;
}
buffer_append(&data, data_blob, dlen);
debug3("found certificate option \"%.100s\" len %u",
name, dlen);
if (strlen(name) != nlen) {
error("Certificate constraint name contains \\0");
goto out;
}
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 ((command = buffer_get_cstring_ret(&data,
&clen)) == NULL) {
error("Certificate constraint \"%s\" "
"corrupt", name);
goto out;
}
if (strlen(command) != clen) {
error("force-command constraint "
"contains \\0");
goto out;
}
if (*cert_forced_command != NULL) {
error("Certificate has multiple "
"force-command options");
xfree(command);
goto out;
}
*cert_forced_command = command;
found = 1;
}
if (strcmp(name, "source-address") == 0) {
if ((allowed = buffer_get_cstring_ret(&data,
&clen)) == NULL) {
error("Certificate constraint "
"\"%s\" corrupt", name);
goto out;
}
if (strlen(allowed) != clen) {
error("source-address constraint "
"contains \\0");
goto out;
}
if ((*cert_source_address_done)++) {
error("Certificate has multiple "
"source-address options");
xfree(allowed);
goto out;
}
remote_ip = get_remote_ipaddr();
switch (addr_match_cidr_list(remote_ip,
allowed)) {
case 1:
/* accepted */
xfree(allowed);
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);
xfree(allowed);
goto out;
case -1:
error("Certificate source-address "
"contents invalid");
xfree(allowed);
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 (buffer_len(&data) != 0) {
error("Certificate option \"%s\" corrupt "
"(extra data)", name);
goto out;
}
buffer_clear(&data);
xfree(name);
xfree(data_blob);
name = data_blob = NULL;
}
/* successfully parsed all options */
ret = 0;
out:
if (ret != 0 &&
cert_forced_command != NULL &&
*cert_forced_command != NULL) {
xfree(*cert_forced_command);
*cert_forced_command = NULL;
}
if (name != NULL)
xfree(name);
if (data_blob != NULL)
xfree(data_blob);
buffer_free(&data);
buffer_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(Key *k, struct passwd *pw)
{
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;
if (key_cert_is_legacy(k)) {
/* All options are in the one field for v00 certs */
if (parse_option_list(buffer_ptr(&k->cert->critical),
buffer_len(&k->cert->critical), pw,
OPTIONS_CRITICAL|OPTIONS_EXTENSIONS, 1,
&cert_no_port_forwarding_flag,
&cert_no_agent_forwarding_flag,
&cert_no_x11_forwarding_flag,
&cert_no_pty_flag,
&cert_no_user_rc,
&cert_forced_command,
&cert_source_address_done) == -1)
return -1;
} else {
/* Separate options and extensions for v01 certs */
if (parse_option_list(buffer_ptr(&k->cert->critical),
buffer_len(&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(buffer_ptr(&k->cert->extensions),
buffer_len(&k->cert->extensions), pw,
OPTIONS_EXTENSIONS, 1,
&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;
/* CA-specified forced command supersedes key option */
if (cert_forced_command != NULL) {
if (forced_command != NULL)
xfree(forced_command);
forced_command = cert_forced_command;
}
return 0;
}
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