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upstream: Add RequiredRSASize for sshd(8); RSA keys that fall 

beneath this limit will be ignored for user and host-based authentication.

Feedback deraadt@ ok markus@

OpenBSD-Commit-ID: 187931dfc19d51873df5930a04f2d972adf1f7f1
This commit is contained in:
djm@openbsd.org 2022-09-17 10:34:29 +00:00 committed by Damien Miller
parent 54b333d12e
commit 1875042c52
No known key found for this signature in database
6 changed files with 46 additions and 7 deletions
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7
auth2-hostbased.c
View File

@ -1,4 +1,4 @@
/* $OpenBSD: auth2-hostbased.c,v 1.49 2022/01/06 22:01:14 djm Exp $ */
/* $OpenBSD: auth2-hostbased.c,v 1.50 2022/09/17 10:34:29 djm Exp $ */
/*
* Copyright (c) 2000 Markus Friedl. All rights reserved.
*
@ -119,6 +119,11 @@ userauth_hostbased(struct ssh *ssh, const char *method)
"(null)" : key->cert->signature_type);
goto done;
}
if ((r = sshkey_check_rsa_length(key,
options.required_rsa_size)) != 0) {
logit_r(r, "refusing %s key", sshkey_type(key));
goto done;
}
if (!authctxt->valid || authctxt->user == NULL) {
debug2_f("disabled because of invalid user");

7
auth2-pubkey.c
View File

@ -1,4 +1,4 @@
/* $OpenBSD: auth2-pubkey.c,v 1.116 2022/06/15 16:08:25 djm Exp $ */
/* $OpenBSD: auth2-pubkey.c,v 1.117 2022/09/17 10:34:29 djm Exp $ */
/*
* Copyright (c) 2000 Markus Friedl. All rights reserved.
* Copyright (c) 2010 Damien Miller. All rights reserved.
@ -175,6 +175,11 @@ userauth_pubkey(struct ssh *ssh, const char *method)
"(null)" : key->cert->signature_type);
goto done;
}
if ((r = sshkey_check_rsa_length(key,
options.required_rsa_size)) != 0) {
logit_r(r, "refusing %s key", sshkey_type(key));
goto done;
}
key_s = format_key(key);
if (sshkey_is_cert(key))
ca_s = format_key(key->cert->signature_key);

13
servconf.c
View File

@ -1,5 +1,5 @@
/* $OpenBSD: servconf.c,v 1.385 2022/06/03 04:30:47 djm Exp $ */
/* $OpenBSD: servconf.c,v 1.386 2022/09/17 10:34:29 djm Exp $ */
/*
* Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
* All rights reserved
@ -195,6 +195,7 @@ initialize_server_options(ServerOptions *options)
options->fingerprint_hash = -1;
options->disable_forwarding = -1;
options->expose_userauth_info = -1;
options->required_rsa_size = -1;
}
/* Returns 1 if a string option is unset or set to "none" or 0 otherwise. */
@ -441,6 +442,8 @@ fill_default_server_options(ServerOptions *options)
options->expose_userauth_info = 0;
if (options->sk_provider == NULL)
options->sk_provider = xstrdup("internal");
if (options->required_rsa_size == -1)
options->required_rsa_size = SSH_RSA_MINIMUM_MODULUS_SIZE;
assemble_algorithms(options);
@ -517,6 +520,7 @@ typedef enum {
sStreamLocalBindMask, sStreamLocalBindUnlink,
sAllowStreamLocalForwarding, sFingerprintHash, sDisableForwarding,
sExposeAuthInfo, sRDomain, sPubkeyAuthOptions, sSecurityKeyProvider,
sRequiredRSASize,
sDeprecated, sIgnore, sUnsupported
} ServerOpCodes;
@ -676,6 +680,7 @@ static struct {
{ "rdomain", sRDomain, SSHCFG_ALL },
{ "casignaturealgorithms", sCASignatureAlgorithms, SSHCFG_ALL },
{ "securitykeyprovider", sSecurityKeyProvider, SSHCFG_GLOBAL },
{ "requiredrsasize", sRequiredRSASize, SSHCFG_ALL },
{ NULL, sBadOption, 0 }
};
@ -2438,6 +2443,10 @@ process_server_config_line_depth(ServerOptions *options, char *line,
*charptr = xstrdup(arg);
break;
case sRequiredRSASize:
intptr = &options->required_rsa_size;
goto parse_int;
case sDeprecated:
case sIgnore:
case sUnsupported:
@ -2610,6 +2619,7 @@ copy_set_server_options(ServerOptions *dst, ServerOptions *src, int preauth)
M_CP_INTOPT(rekey_limit);
M_CP_INTOPT(rekey_interval);
M_CP_INTOPT(log_level);
M_CP_INTOPT(required_rsa_size);
/*
* The bind_mask is a mode_t that may be unsigned, so we can't use
@ -2874,6 +2884,7 @@ dump_config(ServerOptions *o)
dump_cfg_int(sMaxSessions, o->max_sessions);
dump_cfg_int(sClientAliveInterval, o->client_alive_interval);
dump_cfg_int(sClientAliveCountMax, o->client_alive_count_max);
dump_cfg_int(sRequiredRSASize, o->required_rsa_size);
dump_cfg_oct(sStreamLocalBindMask, o->fwd_opts.streamlocal_bind_mask);
/* formatted integer arguments */

3
servconf.h
View File

@ -1,4 +1,4 @@
/* $OpenBSD: servconf.h,v 1.156 2022/03/18 04:04:11 djm Exp $ */
/* $OpenBSD: servconf.h,v 1.157 2022/09/17 10:34:29 djm Exp $ */
/*
* Author: Tatu Ylonen <ylo@cs.hut.fi>
@ -229,6 +229,7 @@ typedef struct {
int expose_userauth_info;
u_int64_t timing_secret;
char *sk_provider;
int required_rsa_size; /* minimum size of RSA keys */
} ServerOptions;
/* Information about the incoming connection as used by Match */

9
sshd.c
View File

@ -1,4 +1,4 @@
/* $OpenBSD: sshd.c,v 1.590 2022/07/01 05:08:23 dtucker Exp $ */
/* $OpenBSD: sshd.c,v 1.591 2022/09/17 10:34:29 djm Exp $ */
/*
* Author: Tatu Ylonen <ylo@cs.hut.fi>
* Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
@ -1870,6 +1870,13 @@ main(int ac, char **av)
fatal_r(r, "Could not demote key: \"%s\"",
options.host_key_files[i]);
}
if (pubkey != NULL && (r = sshkey_check_rsa_length(pubkey,
options.required_rsa_size)) != 0) {
error_fr(r, "Host key %s", options.host_key_files[i]);
sshkey_free(pubkey);
sshkey_free(key);
continue;
}
sensitive_data.host_keys[i] = key;
sensitive_data.host_pubkeys[i] = pubkey;

14
sshd_config.5
View File

@ -33,8 +33,8 @@
.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
.\"
.\" $OpenBSD: sshd_config.5,v 1.342 2022/06/24 04:27:14 djm Exp $
.Dd $Mdocdate: June 24 2022 $
.\" $OpenBSD: sshd_config.5,v 1.343 2022/09/17 10:34:29 djm Exp $
.Dd $Mdocdate: September 17 2022 $
.Dt SSHD_CONFIG 5
.Os
.Sh NAME
@ -1596,6 +1596,16 @@ is
.Cm default none ,
which means that rekeying is performed after the cipher's default amount
of data has been sent or received and no time based rekeying is done.
.It Cm RequiredRSASize
Specifies the minimum RSA key size (in bits) that
.Xr sshd 8
will accept.
User and host-based authentication keys smaller than this limit will be
refused.
The default is
.Cm 1024
bits.
Note that this limit may only be raised from the default.
.It Cm RevokedKeys
Specifies revoked public keys file, or
.Cm none