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upstream: add a RequiredRSASize for checking RSA key length in

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ssh(1). User authentication keys that fall beneath this limit will be
ignored. If a host presents a host key beneath this limit then the connection
will be terminated (unfortunately there are no fallbacks in the protocol for
host authentication).

feedback deraadt, Dmitry Belyavskiy; ok markus@

OpenBSD-Commit-ID: 430e339b2a79fa9ecc63f2837b06fdd88a7da13a
This commit is contained in:
djm@openbsd.org 2022-09-17 10:33:18 +00:00 committed by Damien Miller
parent 07d8771bac
commit 54b333d12e
No known key found for this signature in database
6 changed files with 67 additions and 17 deletions
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13
readconf.c
View File

@ -1,4 +1,4 @@
/* $OpenBSD: readconf.c,v 1.368 2022/06/03 04:30:47 djm Exp $ */ /* $OpenBSD: readconf.c,v 1.369 2022/09/17 10:33:18 djm Exp $ */
/* /*
* Author: Tatu Ylonen <ylo@cs.hut.fi> * Author: Tatu Ylonen <ylo@cs.hut.fi>
* Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
@ -174,7 +174,7 @@ typedef enum {
oStreamLocalBindMask, oStreamLocalBindUnlink, oRevokedHostKeys, oStreamLocalBindMask, oStreamLocalBindUnlink, oRevokedHostKeys,
oFingerprintHash, oUpdateHostkeys, oHostbasedAcceptedAlgorithms, oFingerprintHash, oUpdateHostkeys, oHostbasedAcceptedAlgorithms,
oPubkeyAcceptedAlgorithms, oCASignatureAlgorithms, oProxyJump, oPubkeyAcceptedAlgorithms, oCASignatureAlgorithms, oProxyJump,
oSecurityKeyProvider, oKnownHostsCommand, oSecurityKeyProvider, oKnownHostsCommand, oRequiredRSASize,
oIgnore, oIgnoredUnknownOption, oDeprecated, oUnsupported oIgnore, oIgnoredUnknownOption, oDeprecated, oUnsupported
} OpCodes; } OpCodes;
@ -320,6 +320,7 @@ static struct {
{ "proxyjump", oProxyJump }, { "proxyjump", oProxyJump },
{ "securitykeyprovider", oSecurityKeyProvider }, { "securitykeyprovider", oSecurityKeyProvider },
{ "knownhostscommand", oKnownHostsCommand }, { "knownhostscommand", oKnownHostsCommand },
{ "requiredrsasize", oRequiredRSASize },
{ NULL, oBadOption } { NULL, oBadOption }
}; };
@ -2176,6 +2177,10 @@ parse_pubkey_algos:
*charptr = xstrdup(arg); *charptr = xstrdup(arg);
break; break;
case oRequiredRSASize:
intptr = &options->required_rsa_size;
goto parse_int;
case oDeprecated: case oDeprecated:
debug("%s line %d: Deprecated option \"%s\"", debug("%s line %d: Deprecated option \"%s\"",
filename, linenum, keyword); filename, linenum, keyword);
@ -2423,6 +2428,7 @@ initialize_options(Options * options)
options->hostbased_accepted_algos = NULL; options->hostbased_accepted_algos = NULL;
options->pubkey_accepted_algos = NULL; options->pubkey_accepted_algos = NULL;
options->known_hosts_command = NULL; options->known_hosts_command = NULL;
options->required_rsa_size = -1;
} }
/* /*
@ -2619,6 +2625,8 @@ fill_default_options(Options * options)
if (options->sk_provider == NULL) if (options->sk_provider == NULL)
options->sk_provider = xstrdup("$SSH_SK_PROVIDER"); options->sk_provider = xstrdup("$SSH_SK_PROVIDER");
#endif #endif
if (options->required_rsa_size == -1)
options->required_rsa_size = SSH_RSA_MINIMUM_MODULUS_SIZE;
/* Expand KEX name lists */ /* Expand KEX name lists */
all_cipher = cipher_alg_list(',', 0); all_cipher = cipher_alg_list(',', 0);
@ -3308,6 +3316,7 @@ dump_client_config(Options *o, const char *host)
dump_cfg_int(oNumberOfPasswordPrompts, o->number_of_password_prompts); dump_cfg_int(oNumberOfPasswordPrompts, o->number_of_password_prompts);
dump_cfg_int(oServerAliveCountMax, o->server_alive_count_max); dump_cfg_int(oServerAliveCountMax, o->server_alive_count_max);
dump_cfg_int(oServerAliveInterval, o->server_alive_interval); dump_cfg_int(oServerAliveInterval, o->server_alive_interval);
dump_cfg_int(oRequiredRSASize, o->required_rsa_size);
/* String options */ /* String options */
dump_cfg_string(oBindAddress, o->bind_address); dump_cfg_string(oBindAddress, o->bind_address);

4
readconf.h
View File

@ -1,4 +1,4 @@
/* $OpenBSD: readconf.h,v 1.147 2022/06/03 04:30:47 djm Exp $ */ /* $OpenBSD: readconf.h,v 1.148 2022/09/17 10:33:18 djm Exp $ */
/* /*
* Author: Tatu Ylonen <ylo@cs.hut.fi> * Author: Tatu Ylonen <ylo@cs.hut.fi>
@ -176,6 +176,8 @@ typedef struct {
char *known_hosts_command; char *known_hosts_command;
int required_rsa_size; /* minimum size of RSA keys */
char *ignored_unknown; /* Pattern list of unknown tokens to ignore */ char *ignored_unknown; /* Pattern list of unknown tokens to ignore */
} Options; } Options;

5
ssh.1
View File

@ -33,8 +33,8 @@
.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF .\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. .\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
.\" .\"
.\" $OpenBSD: ssh.1,v 1.431 2022/05/28 05:57:56 jmc Exp $ .\" $OpenBSD: ssh.1,v 1.432 2022/09/17 10:33:18 djm Exp $
.Dd $Mdocdate: May 28 2022 $ .Dd $Mdocdate: September 17 2022 $
.Dt SSH 1 .Dt SSH 1
.Os .Os
.Sh NAME .Sh NAME
@ -571,6 +571,7 @@ For full details of the options listed below, and their possible values, see
.It RemoteCommand .It RemoteCommand
.It RemoteForward .It RemoteForward
.It RequestTTY .It RequestTTY
.It RequiredRSASize
.It SendEnv .It SendEnv
.It ServerAliveInterval .It ServerAliveInterval
.It ServerAliveCountMax .It ServerAliveCountMax

27
ssh.c
View File

@ -1,4 +1,4 @@
/* $OpenBSD: ssh.c,v 1.575 2022/07/01 00:36:30 djm Exp $ */ /* $OpenBSD: ssh.c,v 1.576 2022/09/17 10:33:18 djm Exp $ */
/* /*
* Author: Tatu Ylonen <ylo@cs.hut.fi> * Author: Tatu Ylonen <ylo@cs.hut.fi>
* Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
@ -516,14 +516,22 @@ resolve_canonicalize(char **hostp, int port)
} }
/* /*
* Check the result of hostkey loading, ignoring some errors and * Check the result of hostkey loading, ignoring some errors and either
* fatal()ing for others. * discarding the key or fatal()ing for others.
*/ */
static void static void
check_load(int r, const char *path, const char *message) check_load(int r, struct sshkey **k, const char *path, const char *message)
{ {
switch (r) { switch (r) {
case 0: case 0:
/* Check RSA keys size and discard if undersized */
if (k != NULL && *k != NULL &&
(r = sshkey_check_rsa_length(*k,
options.required_rsa_size)) != 0) {
error_r(r, "load %s \"%s\"", message, path);
free(*k);
*k = NULL;
}
break; break;
case SSH_ERR_INTERNAL_ERROR: case SSH_ERR_INTERNAL_ERROR:
case SSH_ERR_ALLOC_FAIL: case SSH_ERR_ALLOC_FAIL:
@ -1578,7 +1586,7 @@ main(int ac, char **av)
if ((o) >= sensitive_data.nkeys) \ if ((o) >= sensitive_data.nkeys) \
fatal_f("pubkey out of array bounds"); \ fatal_f("pubkey out of array bounds"); \
check_load(sshkey_load_public(p, &(sensitive_data.keys[o]), NULL), \ check_load(sshkey_load_public(p, &(sensitive_data.keys[o]), NULL), \
p, "pubkey"); \ &(sensitive_data.keys[o]), p, "pubkey"); \
if (sensitive_data.keys[o] != NULL) \ if (sensitive_data.keys[o] != NULL) \
debug2("hostbased key %d: %s key from \"%s\"", o, \ debug2("hostbased key %d: %s key from \"%s\"", o, \
sshkey_ssh_name(sensitive_data.keys[o]), p); \ sshkey_ssh_name(sensitive_data.keys[o]), p); \
@ -1586,7 +1594,8 @@ main(int ac, char **av)
#define L_CERT(p,o) do { \ #define L_CERT(p,o) do { \
if ((o) >= sensitive_data.nkeys) \ if ((o) >= sensitive_data.nkeys) \
fatal_f("cert out of array bounds"); \ fatal_f("cert out of array bounds"); \
check_load(sshkey_load_cert(p, &(sensitive_data.keys[o])), p, "cert"); \ check_load(sshkey_load_cert(p, &(sensitive_data.keys[o])), \
&(sensitive_data.keys[o]), p, "cert"); \
if (sensitive_data.keys[o] != NULL) \ if (sensitive_data.keys[o] != NULL) \
debug2("hostbased key %d: %s cert from \"%s\"", o, \ debug2("hostbased key %d: %s cert from \"%s\"", o, \
sshkey_ssh_name(sensitive_data.keys[o]), p); \ sshkey_ssh_name(sensitive_data.keys[o]), p); \
@ -2265,7 +2274,7 @@ load_public_identity_files(const struct ssh_conn_info *cinfo)
filename = default_client_percent_dollar_expand(cp, cinfo); filename = default_client_percent_dollar_expand(cp, cinfo);
free(cp); free(cp);
check_load(sshkey_load_public(filename, &public, NULL), check_load(sshkey_load_public(filename, &public, NULL),
filename, "pubkey"); &public, filename, "pubkey");
debug("identity file %s type %d", filename, debug("identity file %s type %d", filename,
public ? public->type : -1); public ? public->type : -1);
free(options.identity_files[i]); free(options.identity_files[i]);
@ -2284,7 +2293,7 @@ load_public_identity_files(const struct ssh_conn_info *cinfo)
continue; continue;
xasprintf(&cp, "%s-cert", filename); xasprintf(&cp, "%s-cert", filename);
check_load(sshkey_load_public(cp, &public, NULL), check_load(sshkey_load_public(cp, &public, NULL),
filename, "pubkey"); &public, filename, "pubkey");
debug("identity file %s type %d", cp, debug("identity file %s type %d", cp,
public ? public->type : -1); public ? public->type : -1);
if (public == NULL) { if (public == NULL) {
@ -2315,7 +2324,7 @@ load_public_identity_files(const struct ssh_conn_info *cinfo)
free(cp); free(cp);
check_load(sshkey_load_public(filename, &public, NULL), check_load(sshkey_load_public(filename, &public, NULL),
filename, "certificate"); &public, filename, "certificate");
debug("certificate file %s type %d", filename, debug("certificate file %s type %d", filename,
public ? public->type : -1); public ? public->type : -1);
free(options.certificate_files[i]); free(options.certificate_files[i]);

15
ssh_config.5
View File

@ -33,8 +33,8 @@
.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF .\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. .\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
.\" .\"
.\" $OpenBSD: ssh_config.5,v 1.373 2022/06/24 04:27:14 djm Exp $ .\" $OpenBSD: ssh_config.5,v 1.374 2022/09/17 10:33:18 djm Exp $
.Dd $Mdocdate: June 24 2022 $ .Dd $Mdocdate: September 17 2022 $
.Dt SSH_CONFIG 5 .Dt SSH_CONFIG 5
.Os .Os
.Sh NAME .Sh NAME
@ -1634,6 +1634,17 @@ and
.Fl T .Fl T
flags for flags for
.Xr ssh 1 . .Xr ssh 1 .
.It Cm RequiredRSASize
Specifies the minimum RSA key size (in bits) that
.Xr ssh 1
will accept.
User authentication keys smaller than this limit will be ignored.
Servers that present host keys smaller than this limit will cause the
connection to be terminated.
The default is
.Cm 1024
bits.
Note that this limit may only be raised from the default.
.It Cm RevokedHostKeys .It Cm RevokedHostKeys
Specifies revoked host public keys. Specifies revoked host public keys.
Keys listed in this file will be refused for host authentication. Keys listed in this file will be refused for host authentication.

20
sshconnect2.c
View File

@ -1,4 +1,4 @@
/* $OpenBSD: sshconnect2.c,v 1.360 2022/08/19 06:07:47 djm Exp $ */ /* $OpenBSD: sshconnect2.c,v 1.361 2022/09/17 10:33:18 djm Exp $ */
/* /*
* Copyright (c) 2000 Markus Friedl. All rights reserved. * Copyright (c) 2000 Markus Friedl. All rights reserved.
* Copyright (c) 2008 Damien Miller. All rights reserved. * Copyright (c) 2008 Damien Miller. All rights reserved.
@ -96,6 +96,11 @@ static const struct ssh_conn_info *xxx_conn_info;
static int static int
verify_host_key_callback(struct sshkey *hostkey, struct ssh *ssh) verify_host_key_callback(struct sshkey *hostkey, struct ssh *ssh)
{ {
int r;
if ((r = sshkey_check_rsa_length(hostkey,
options.required_rsa_size)) != 0)
fatal_r(r, "Bad server host key");
if (verify_host_key(xxx_host, xxx_hostaddr, hostkey, if (verify_host_key(xxx_host, xxx_hostaddr, hostkey,
xxx_conn_info) == -1) xxx_conn_info) == -1)
fatal("Host key verification failed."); fatal("Host key verification failed.");
@ -1606,6 +1611,13 @@ load_identity_file(Identity *id)
private = NULL; private = NULL;
quit = 1; quit = 1;
} }
if (!quit && (r = sshkey_check_rsa_length(private,
options.required_rsa_size)) != 0) {
debug_fr(r, "Skipping key %s", id->filename);
sshkey_free(private);
private = NULL;
quit = 1;
}
if (!quit && private != NULL && id->agent_fd == -1 && if (!quit && private != NULL && id->agent_fd == -1 &&
!(id->key && id->isprivate)) !(id->key && id->isprivate))
maybe_add_key_to_agent(id->filename, private, comment, maybe_add_key_to_agent(id->filename, private, comment,
@ -1752,6 +1764,12 @@ pubkey_prepare(struct ssh *ssh, Authctxt *authctxt)
/* list of keys supported by the agent */ /* list of keys supported by the agent */
if ((r = get_agent_identities(ssh, &agent_fd, &idlist)) == 0) { if ((r = get_agent_identities(ssh, &agent_fd, &idlist)) == 0) {
for (j = 0; j < idlist->nkeys; j++) { for (j = 0; j < idlist->nkeys; j++) {
if ((r = sshkey_check_rsa_length(idlist->keys[j],
options.required_rsa_size)) != 0) {
debug_fr(r, "ignoring %s agent key",
sshkey_ssh_name(idlist->keys[j]));
continue;
}
found = 0; found = 0;
TAILQ_FOREACH(id, &files, next) { TAILQ_FOREACH(id, &files, next) {
/* /*