openssh/openssh-8.7p1-minrsabits.patch

diff --git a/auth2-hostbased.c b/auth2-hostbased.c
index 2ab222ed6..4e9437912 100644
--- a/auth2-hostbased.c
+++ b/auth2-hostbased.c
@@ -118,6 +118,10 @@ userauth_hostbased(struct ssh *ssh, const char *method)
 		    "(null)" : key->cert->signature_type);
 		goto done;
 	}
+	if ((r = sshkey_check_rsa_length(key, options.rsa_min_size)) != 0) {
+		logit("refusing %s key", sshkey_type(key));
+		goto done;
+	}
 
 	if (!authctxt->valid || authctxt->user == NULL) {
 		debug2_f("disabled because of invalid user");
diff --git a/auth2-pubkey.c b/auth2-pubkey.c
index daa756a01..68e7dea1f 100644
--- a/auth2-pubkey.c
+++ b/auth2-pubkey.c
@@ -172,6 +172,10 @@ userauth_pubkey(struct ssh *ssh, const char *method)
 		    "(null)" : key->cert->signature_type);
 		goto done;
 	}
+	if ((r = sshkey_check_rsa_length(key, options.rsa_min_size)) != 0) {
+		logit("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);
diff --git a/readconf.c b/readconf.c
index 5b5afa8e3..5e17abd41 100644
--- a/readconf.c
+++ b/readconf.c
@@ -160,7 +160,7 @@ typedef enum {
 	oStreamLocalBindMask, oStreamLocalBindUnlink, oRevokedHostKeys,
 	oFingerprintHash, oUpdateHostkeys, oHostbasedAcceptedAlgorithms,
 	oPubkeyAcceptedAlgorithms, oCASignatureAlgorithms, oProxyJump,
-	oSecurityKeyProvider, oKnownHostsCommand,
+	oSecurityKeyProvider, oKnownHostsCommand, oRSAMinSize,
 	oIgnore, oIgnoredUnknownOption, oDeprecated, oUnsupported
 } OpCodes;
 
@@ -306,6 +306,7 @@ static struct {
 	{ "proxyjump", oProxyJump },
 	{ "securitykeyprovider", oSecurityKeyProvider },
 	{ "knownhostscommand", oKnownHostsCommand },
+	{ "rsaminsize", oRSAMinSize },
 
 	{ NULL, oBadOption }
 };
@@ -2162,6 +2163,10 @@ process_config_line_depth(Options *options, struct passwd *pw, const char *host,
 			*charptr = xstrdup(arg);
 		break;
 
+	case oRSAMinSize:
+		intptr = &options->rsa_min_size;
+		goto parse_int;
+
 	case oDeprecated:
 		debug("%s line %d: Deprecated option \"%s\"",
 		    filename, linenum, keyword);
@@ -2409,6 +2414,7 @@ initialize_options(Options * options)
 	options->hostbased_accepted_algos = NULL;
 	options->pubkey_accepted_algos = NULL;
 	options->known_hosts_command = NULL;
+	options->rsa_min_size = -1;
 }
 
 /*
@@ -2598,6 +2604,8 @@ fill_default_options(Options * options)
 	if (options->sk_provider == NULL)
 		options->sk_provider = xstrdup("$SSH_SK_PROVIDER");
 #endif
+	if (options->rsa_min_size == -1)
+		options->rsa_min_size = SSH_RSA_MINIMUM_MODULUS_SIZE;
 
 	/* Expand KEX name lists */
 	all_cipher = cipher_alg_list(',', 0);
@@ -3287,6 +3295,7 @@ dump_client_config(Options *o, const char *host)
 	dump_cfg_int(oNumberOfPasswordPrompts, o->number_of_password_prompts);
 	dump_cfg_int(oServerAliveCountMax, o->server_alive_count_max);
 	dump_cfg_int(oServerAliveInterval, o->server_alive_interval);
+	dump_cfg_int(oRSAMinSize, o->rsa_min_size);
 
 	/* String options */
 	dump_cfg_string(oBindAddress, o->bind_address);
diff --git a/readconf.h b/readconf.h
index f647bd42a..29db353ab 100644
--- a/readconf.h
+++ b/readconf.h
@@ -176,6 +176,8 @@ typedef struct {
 
 	char   *known_hosts_command;
 
+	int	rsa_min_size;	/* minimum size of RSA keys */
+
 	char	*ignored_unknown; /* Pattern list of unknown tokens to ignore */
 }       Options;
 
diff --git a/servconf.c b/servconf.c
index f7317a5cb..362ff5b67 100644
--- a/servconf.c
+++ b/servconf.c
@@ -177,6 +177,7 @@ initialize_server_options(ServerOptions *options)
 	options->fingerprint_hash = -1;
 	options->disable_forwarding = -1;
 	options->expose_userauth_info = -1;
+	options->rsa_min_size = -1;
 }
 
 /* Returns 1 if a string option is unset or set to "none" or 0 otherwise. */
@@ -416,6 +417,8 @@ fill_default_server_options(ServerOptions *options)
 		options->expose_userauth_info = 0;
 	if (options->sk_provider == NULL)
 		options->sk_provider = xstrdup("internal");
+	if (options->rsa_min_size == -1)
+		options->rsa_min_size = SSH_RSA_MINIMUM_MODULUS_SIZE;
 
 	assemble_algorithms(options);
 
@@ -489,6 +492,7 @@ typedef enum {
 	sStreamLocalBindMask, sStreamLocalBindUnlink,
 	sAllowStreamLocalForwarding, sFingerprintHash, sDisableForwarding,
 	sExposeAuthInfo, sRDomain, sPubkeyAuthOptions, sSecurityKeyProvider,
+	sRSAMinSize,
 	sDeprecated, sIgnore, sUnsupported
 } ServerOpCodes;
 
@@ -632,6 +636,7 @@ static struct {
 	{ "rdomain", sRDomain, SSHCFG_ALL },
 	{ "casignaturealgorithms", sCASignatureAlgorithms, SSHCFG_ALL },
 	{ "securitykeyprovider", sSecurityKeyProvider, SSHCFG_GLOBAL },
+	{ "rsaminsize", sRSAMinSize, SSHCFG_ALL },
 	{ NULL, sBadOption, 0 }
 };
 
@@ -2377,6 +2382,10 @@ process_server_config_line_depth(ServerOptions *options, char *line,
 			*charptr = xstrdup(arg);
 		break;
 
+	case sRSAMinSize:
+		intptr = &options->rsa_min_size;
+		goto parse_int;
+
 	case sDeprecated:
 	case sIgnore:
 	case sUnsupported:
@@ -2549,6 +2558,7 @@ 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(rsa_min_size);
 
 	/*
 	 * The bind_mask is a mode_t that may be unsigned, so we can't use
@@ -2810,6 +2820,7 @@ 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(sRSAMinSize, o->rsa_min_size);
 	dump_cfg_oct(sStreamLocalBindMask, o->fwd_opts.streamlocal_bind_mask);
 
 	/* formatted integer arguments */
diff --git a/servconf.h b/servconf.h
index 115db1e79..2e3486906 100644
--- a/servconf.h
+++ b/servconf.h
@@ -227,6 +227,7 @@ typedef struct {
 	int	expose_userauth_info;
 	u_int64_t timing_secret;
 	char   *sk_provider;
+	int	rsa_min_size;	/* minimum size of RSA keys */
 }       ServerOptions;
 
 /* Information about the incoming connection as used by Match */
diff --git a/ssh.c b/ssh.c
index a926cc007..cd13fb879 100644
--- a/ssh.c
+++ b/ssh.c
@@ -500,14 +500,22 @@ resolve_canonicalize(char **hostp, int port)
 }
 
 /*
- * Check the result of hostkey loading, ignoring some errors and
- * fatal()ing for others.
+ * Check the result of hostkey loading, ignoring some errors and either
+ * discarding the key or fatal()ing for others.
  */
 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) {
 	case 0:
+		/* Check RSA keys size and discard if undersized */
+		if (k != NULL && *k != NULL &&
+		    (r = sshkey_check_rsa_length(*k,
+		    options.rsa_min_size)) != 0) {
+			error_r(r, "load %s \"%s\"", message, path);
+			free(*k);
+			*k = NULL;
+		}
 		break;
 	case SSH_ERR_INTERNAL_ERROR:
 	case SSH_ERR_ALLOC_FAIL:
@@ -1557,12 +1565,13 @@ main(int ac, char **av)
 	if ((o) >= sensitive_data.nkeys) \
 		fatal_f("pubkey out of array bounds"); \
 	check_load(sshkey_load_public(p, &(sensitive_data.keys[o]), NULL), \
-	    p, "pubkey"); \
+	    &(sensitive_data.keys[o]), p, "pubkey"); \
 } while (0)
 #define L_CERT(p,o) do { \
 	if ((o) >= sensitive_data.nkeys) \
 		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"); \
 } while (0)
 
 		if (options.hostbased_authentication == 1) {
@@ -2244,7 +2253,7 @@ load_public_identity_files(const struct ssh_conn_info *cinfo)
 		filename = default_client_percent_dollar_expand(cp, cinfo);
 		free(cp);
 		check_load(sshkey_load_public(filename, &public, NULL),
-		    filename, "pubkey");
+		    &public, filename, "pubkey");
 		debug("identity file %s type %d", filename,
 		    public ? public->type : -1);
 		free(options.identity_files[i]);
@@ -2263,7 +2272,7 @@ load_public_identity_files(const struct ssh_conn_info *cinfo)
 			continue;
 		xasprintf(&cp, "%s-cert", filename);
 		check_load(sshkey_load_public(cp, &public, NULL),
-		    filename, "pubkey");
+		    &public, filename, "pubkey");
 		debug("identity file %s type %d", cp,
 		    public ? public->type : -1);
 		if (public == NULL) {
@@ -2294,7 +2303,7 @@ load_public_identity_files(const struct ssh_conn_info *cinfo)
 		free(cp);
 
 		check_load(sshkey_load_public(filename, &public, NULL),
-		    filename, "certificate");
+		    &public, filename, "certificate");
 		debug("certificate file %s type %d", filename,
 		    public ? public->type : -1);
 		free(options.certificate_files[i]);
diff --git a/sshconnect2.c b/sshconnect2.c
index 67f8e0309..d050c1656 100644
--- a/sshconnect2.c
+++ b/sshconnect2.c
@@ -91,6 +91,10 @@ static const struct ssh_conn_info *xxx_conn_info;
 static int
 verify_host_key_callback(struct sshkey *hostkey, struct ssh *ssh)
 {
+	int r;
+
+	if ((r = sshkey_check_rsa_length(hostkey, options.rsa_min_size)) != 0)
+		fatal_r(r, "Bad server host key");
 	if (verify_host_key(xxx_host, xxx_hostaddr, hostkey,
 	    xxx_conn_info) == -1)
 		fatal("Host key verification failed.");
@@ -1762,6 +1762,12 @@ load_identity_file(Identity *id)
 			private = NULL;
 			quit = 1;
 		}
+		if (r = sshkey_check_rsa_length(private, options.rsa_min_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 &&
 		    !(id->key && id->isprivate))
 			maybe_add_key_to_agent(id->filename, private, comment,
@@ -1747,6 +1751,12 @@ pubkey_prepare(struct ssh *ssh, Authctxt *authctxt)
		close(agent_fd);
	} else {
 		for (j = 0; j < idlist->nkeys; j++) {
+			if ((r = sshkey_check_rsa_length(idlist->keys[j],
+			    options.rsa_min_size)) != 0) {
+				debug_fr(r, "ignoring %s agent key",
+				    sshkey_ssh_name(idlist->keys[j]));
+				continue;
+			}
 			found = 0;
 			TAILQ_FOREACH(id, &files, next) {
 				/*
diff --git a/sshd.c b/sshd.c
index d26eb86ae..5f36905a1 100644
--- a/sshd.c
+++ b/sshd.c
@@ -1746,6 +1746,13 @@ 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.rsa_min_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;
 
diff --git a/sshkey.c b/sshkey.c
index 47864e6d8..8bad6bd99 100644
--- a/sshkey.c
+++ b/sshkey.c
@@ -2319,18 +2319,24 @@ cert_parse(struct sshbuf *b, struct sshkey *key, struct sshbuf *certbuf)
 	return ret;
 }
 
-#ifdef WITH_OPENSSL
-static int
-check_rsa_length(const RSA *rsa)
+int
+sshkey_check_rsa_length(const struct sshkey *k, int min_size)
 {
+#ifdef WITH_OPENSSL
 	const BIGNUM *rsa_n;
+	int nbits;
 
-	RSA_get0_key(rsa, &rsa_n, NULL, NULL);
-	if (BN_num_bits(rsa_n) < SSH_RSA_MINIMUM_MODULUS_SIZE)
+	if (k == NULL || k->rsa == NULL ||
+	    (k->type != KEY_RSA && k->type != KEY_RSA_CERT))
+		return 0;
+	RSA_get0_key(k->rsa, &rsa_n, NULL, NULL);
+	nbits = BN_num_bits(rsa_n);
+	if (nbits < SSH_RSA_MINIMUM_MODULUS_SIZE ||
+	    (min_size > 0 && nbits < min_size))
 		return SSH_ERR_KEY_LENGTH;
+#endif /* WITH_OPENSSL */
 	return 0;
 }
-#endif
 
 static int
 sshkey_from_blob_internal(struct sshbuf *b, struct sshkey **keyp,
@@ -2391,7 +2397,7 @@ sshkey_from_blob_internal(struct sshbuf *b, struct sshkey **keyp,
 			goto out;
 		}
 		rsa_n = rsa_e = NULL; /* transferred */
-		if ((ret = check_rsa_length(key->rsa)) != 0)
+		if ((ret = sshkey_check_rsa_length(key, 0)) != 0)
 			goto out;
 #ifdef DEBUG_PK
 		RSA_print_fp(stderr, key->rsa, 8);
@@ -3580,7 +3586,7 @@ sshkey_private_deserialize(struct sshbuf *buf, struct sshkey **kp)
 			goto out;
 		}
 		rsa_p = rsa_q = NULL; /* transferred */
-		if ((r = check_rsa_length(k->rsa)) != 0)
+		if ((r = sshkey_check_rsa_length(k, 0)) != 0)
 			goto out;
 		if ((r = ssh_rsa_complete_crt_parameters(k, rsa_iqmp)) != 0)
 			goto out;
@@ -4566,7 +4572,7 @@ sshkey_parse_private_pem_fileblob(struct sshbuf *blob, int type,
 			r = SSH_ERR_LIBCRYPTO_ERROR;
 			goto out;
 		}
-		if ((r = check_rsa_length(prv->rsa)) != 0)
+		if ((r = sshkey_check_rsa_length(prv, 0)) != 0)
 			goto out;
 	} else if (EVP_PKEY_base_id(pk) == EVP_PKEY_DSA &&
 	    (type == KEY_UNSPEC || type == KEY_DSA)) {
diff --git a/sshkey.h b/sshkey.h
index 125cadb64..52e879456 100644
--- a/sshkey.h
+++ b/sshkey.h
@@ -267,6 +267,7 @@ int	sshkey_parse_private_fileblob_type(struct sshbuf *blob, int type,
 int	sshkey_parse_pubkey_from_private_fileblob_type(struct sshbuf *blob,
     int type, struct sshkey **pubkeyp);
 
+int sshkey_check_rsa_length(const struct sshkey *, int);
 /* XXX should be internal, but used by ssh-keygen */
 int ssh_rsa_complete_crt_parameters(struct sshkey *, const BIGNUM *);
 
diff --git a/ssh.1 b/ssh.1
index b4956aec..b1a40ebd 100644
--- a/ssh.1
+++ b/ssh.1
@@ -554,6 +554,7 @@ For full details of the options listed below, and their possible values, see
 .It LogLevel
 .It MACs
 .It Match
+.It RSAMinSize
 .It NoHostAuthenticationForLocalhost
 .It NumberOfPasswordPrompts
 .It PasswordAuthentication
diff --git a/ssh_config.5 b/ssh_config.5
index 24a46460..68771e4b 100644
--- a/ssh_config.5
+++ b/ssh_config.5
@@ -1322,6 +1322,10 @@ The argument to this keyword must be
 or
 .Cm no
 (the default).
+.It Cm RSAMinSize
+Provides a minimal bits requirement for RSA keys when used for signature and
+verification but not for the key generation. The default value is 1024 and
+can't be reduced.
 .It Cm NumberOfPasswordPrompts
 Specifies the number of password prompts before giving up.
 The argument to this keyword must be an integer.
diff --git a/sshd_config.5 b/sshd_config.5
index 867a747d..e08811ca 100644
--- a/sshd_config.5
+++ b/sshd_config.5
@@ -1266,6 +1266,10 @@ will refuse connection attempts with a probability of rate/100 (30%)
 if there are currently start (10) unauthenticated connections.
 The probability increases linearly and all connection attempts
 are refused if the number of unauthenticated connections reaches full (60).
+.It Cm RSAMinSize
+Provides a minimal bits requirement for RSA keys when used for signature and
+verification but not for the key generation. The default value is 1024 and
+can't be reduced.
 .It Cm ModuliFile
 Specifies the
 .Xr moduli 5
diff --git a/sshkey.h b/sshkey.h
index 094815e0..2bb8cb90 100644
--- a/sshkey.h
+++ b/sshkey.h
@@ -286,6 +286,8 @@ int	 sshkey_private_serialize_maxsign(struct sshkey *key,
 
 void	 sshkey_sig_details_free(struct sshkey_sig_details *);
 
+int ssh_set_rsa_min_bits(int minbits);
+
 #ifdef SSHKEY_INTERNAL
 int ssh_rsa_sign(const struct sshkey *key,
     u_char **sigp, size_t *lenp, const u_char *data, size_t datalen,