[PATCH] ssh: Add option to present certificates on command line
Damien Miller
djm at mindrot.org
Thu Jul 30 10:53:24 AEST 2015
Hi,
Thanks for this. Could I ask you to create a bug at
https://bugzilla.mindrot.org/ and attach your patch there? We're pretty
much closed for the 7.0 release ATM but we'll look at it once we're done.
I guess something similar for ssh-add would make sense too...
-d
On Wed, 29 Jul 2015, Meghana Bhat wrote:
> Allow users to specify certificates to be used for authentication on
> the command line with the '-z' argument when running ssh. For
> successful authentication, the key pair associated with the certificate
> must also be presented during the ssh.
>
> Certificates may also be specified in ssh_config as a
> CertificateFile.
>
> This option is meant the address the issue mentioned in the following
> exchange:
> http://lists.mindrot.org/pipermail/openssh-unix-dev/2013-September/031629.html
>
> Patch developed against 6.9p.
>
> ---
> readconf.c | 48 +++++++++++++++++++
> readconf.h | 6 +++
> regress/Makefile | 1 +
> regress/ssh-cert.sh | 136 ++++++++++++++++++++++++++++++++++++++++++++++++++++
> ssh.1 | 17 +++++++
> ssh.c | 85 +++++++++++++++++++++++++++++++-
> ssh.h | 7 +++
> ssh_config.5 | 33 +++++++++++++
> sshconnect2.c | 47 ++++++++++++++++--
> 9 files changed, 375 insertions(+), 5 deletions(-)
> create mode 100644 regress/ssh-cert.sh
>
> diff --git a/readconf.c b/readconf.c
> index f1c860b..b34213d 100644
> --- a/readconf.c
> +++ b/readconf.c
> @@ -135,6 +135,7 @@ typedef enum {
> oPasswordAuthentication, oRSAAuthentication,
> oChallengeResponseAuthentication, oXAuthLocation,
> oIdentityFile, oHostName, oPort, oCipher, oRemoteForward, oLocalForward,
> + oCertificateFile,
> oUser, oEscapeChar, oRhostsRSAAuthentication, oProxyCommand,
> oGlobalKnownHostsFile, oUserKnownHostsFile, oConnectionAttempts,
> oBatchMode, oCheckHostIP, oStrictHostKeyChecking, oCompression,
> @@ -202,6 +203,7 @@ static struct {
> { "identityfile", oIdentityFile },
> { "identityfile2", oIdentityFile }, /* obsolete */
> { "identitiesonly", oIdentitiesOnly },
> + { "certificatefile", oCertificateFile },
> { "hostname", oHostName },
> { "hostkeyalias", oHostKeyAlias },
> { "proxycommand", oProxyCommand },
> @@ -366,6 +368,37 @@ clear_forwardings(Options *options)
> }
>
> void
> +add_certificate_file(Options *options, const char *dir, const char *filename,
> + int userprovided)
> +{
> + char *path;
> + int i;
> +
> + if (options->num_certificate_files >= SSH_MAX_CERTIFICATE_FILES)
> + fatal("Too many certificate files specified (max %d)",
> + SSH_MAX_CERTIFICATE_FILES);
> +
> + if (dir == NULL) /* no dir, filename is absolute */
> + path = xstrdup(filename);
> + else
> + (void)xasprintf(&path, "%.100s%.100s", dir, filename);
> +
> + /* Avoid registering duplicates */
> + for (i = 0; i < options->num_certificate_files; i++) {
> + if (options->certificate_file_userprovided[i] == userprovided &&
> + strcmp(options->certificate_files[i], path) == 0) {
> + debug2("%s: ignoring duplicate key %s", __func__, path);
> + free(path);
> + return;
> + }
> + }
> +
> + options->certificate_file_userprovided[options->num_certificate_files] =
> + userprovided;
> + options->certificate_files[options->num_certificate_files++] = path;
> +}
> +
> +void
> add_identity_file(Options *options, const char *dir, const char *filename,
> int userprovided)
> {
> @@ -981,6 +1014,20 @@ parse_time:
> }
> break;
>
> + case oCertificateFile:
> + arg = strdelim(&s);
> + if (!arg || *arg == '\0')
> + fatal("%.200s line %d: Missing argument.", filename, linenum);
> + if (*activep) {
> + intptr = &options->num_certificate_files;
> + if (*intptr >= SSH_MAX_CERTIFICATE_FILES)
> + fatal("%.200s line %d: Too many identity files specified (max %d).",
> + filename, linenum, SSH_MAX_CERTIFICATE_FILES);
> + add_certificate_file(options, NULL,
> + arg, flags & SSHCONF_USERCONF);
> + }
> + break;
> +
> case oXAuthLocation:
> charptr=&options->xauth_location;
> goto parse_string;
> @@ -1625,6 +1672,7 @@ initialize_options(Options * options)
> options->hostkeyalgorithms = NULL;
> options->protocol = SSH_PROTO_UNKNOWN;
> options->num_identity_files = 0;
> + options->num_certificate_files = 0;
> options->hostname = NULL;
> options->host_key_alias = NULL;
> options->proxy_command = NULL;
> diff --git a/readconf.h b/readconf.h
> index bb2d552..f839016 100644
> --- a/readconf.h
> +++ b/readconf.h
> @@ -94,6 +94,11 @@ typedef struct {
> char *identity_files[SSH_MAX_IDENTITY_FILES];
> int identity_file_userprovided[SSH_MAX_IDENTITY_FILES];
> struct sshkey *identity_keys[SSH_MAX_IDENTITY_FILES];
> +
> + int num_certificate_files; /* Number of extra certificates for ssh. */
> + char *certificate_files[SSH_MAX_CERTIFICATE_FILES];
> + int certificate_file_userprovided[SSH_MAX_CERTIFICATE_FILES];
> + struct sshkey *certificates[SSH_MAX_CERTIFICATE_FILES];
>
> /* Local TCP/IP forward requests. */
> int num_local_forwards;
> @@ -194,5 +199,6 @@ void dump_client_config(Options *o, const char *host);
> void add_local_forward(Options *, const struct Forward *);
> void add_remote_forward(Options *, const struct Forward *);
> void add_identity_file(Options *, const char *, const char *, int);
> +void add_certificate_file(Options *, const char *, const char *, int);
>
> #endif /* READCONF_H */
> diff --git a/regress/Makefile b/regress/Makefile
> index cba83f4..67455a8 100644
> --- a/regress/Makefile
> +++ b/regress/Makefile
> @@ -74,6 +74,7 @@ LTESTS= connect \
> hostkey-agent \
> keygen-knownhosts \
> hostkey-rotate \
> + ssh-cert \
> principals-command
>
>
> diff --git a/regress/ssh-cert.sh b/regress/ssh-cert.sh
> new file mode 100644
> index 0000000..152278b
> --- /dev/null
> +++ b/regress/ssh-cert.sh
> @@ -0,0 +1,136 @@
> +# $OpenBSD: multicert.sh,v 1.1 2014/12/22 08:06:03 djm Exp $
> +# Placed in the Public Domain.
> +
> +tid="ssh with certificates"
> +
> +rm -f $OBJ/user_ca_key* $OBJ/user_key*
> +rm -f $OBJ/cert_user_key*
> +
> +# Create a CA key
> +${SSHKEYGEN} -q -N '' -t ed25519 -f $OBJ/user_ca_key1 ||\
> + fatal "ssh-keygen failed"
> +${SSHKEYGEN} -q -N '' -t ed25519 -f $OBJ/user_ca_key2 ||\
> + fatal "ssh-keygen failed"
> +
> +# Make some keys and certificates.
> +${SSHKEYGEN} -q -N '' -t ed25519 -f $OBJ/user_key1 || \
> + fatal "ssh-keygen failed"
> +${SSHKEYGEN} -q -N '' -t ed25519 -f $OBJ/user_key2 || \
> + fatal "ssh-keygen failed"
> +# Move the certificate to a different address to better control
> +# when it is offered.
> +${SSHKEYGEN} -q -s $OBJ/user_ca_key1 -I "regress user key for $USER" \
> + -z $$ -n ${USER} $OBJ/user_key1 ||
> + fail "couldn't sign user_key1 with user_ca_key1"
> +mv $OBJ/user_key1-cert.pub $OBJ/cert_user_key1_1.pub
> +${SSHKEYGEN} -q -s $OBJ/user_ca_key2 -I "regress user key for $USER" \
> + -z $$ -n ${USER} $OBJ/user_key1 ||
> + fail "couldn't sign user_key1 with user_ca_key2"
> +mv $OBJ/user_key1-cert.pub $OBJ/cert_user_key1_2.pub
> +
> +trace 'try with identity files'
> +opts="-F $OBJ/ssh_proxy -oIdentitiesOnly=yes"
> +opts2="$opts -i $OBJ/user_key1 -i $OBJ/user_key2"
> +echo "cert-authority $(cat $OBJ/user_ca_key1.pub)" > $OBJ/authorized_keys_$USER
> +
> +for p in ${SSH_PROTOCOLS}; do
> + # Just keys should fail
> + ${SSH} $opts2 somehost exit 5$p
> + r=$?
> + if [ $r -eq 5$p ]; then
> + fail "ssh succeeded with no certs in protocol $p"
> + fi
> +
> + # Keys with untrusted cert should fail.
> + opts3="$opts2 -z $OBJ/cert_user_key1_2.pub"
> + ${SSH} $opts3 somehost exit 5$p
> + r=$?
> + if [ $r -eq 5$p ]; then
> + fail "ssh succeeded with bad cert in protocol $p"
> + fi
> +
> + # Good cert with bad key should fail.
> + opts3="$opts -i $OBJ/user_key2 -z $OBJ/cert_user_key1_1.pub"
> + ${SSH} $opts3 somehost exit 5$p
> + r=$?
> + if [ $r -eq 5$p ]; then
> + fail "ssh succeeded with no matching key in protocol $p"
> + fi
> +
> + # Keys with one trusted cert, should succeed.
> + opts3="$opts2 -z $OBJ/cert_user_key1_1.pub"
> + ${SSH} $opts3 somehost exit 5$p
> + r=$?
> + if [ $r -ne 5$p ]; then
> + fail "ssh failed with trusted cert and key in protocol $p"
> + fi
> +
> + # Multiple certs and keys, with one trusted cert, should succeed.
> + opts3="$opts2 -z $OBJ/cert_user_key1_2.pub -z $OBJ/cert_user_key1_1.pub"
> + ${SSH} $opts3 somehost exit 5$p
> + r=$?
> + if [ $r -ne 5$p ]; then
> + fail "ssh failed with multiple certs in protocol $p"
> + fi
> +
> + #Keys with trusted certificate specified in config options, should succeed.
> + opts3="$opts2 -oCertificateFile=$OBJ/cert_user_key1_1.pub"
> + ${SSH} $opts3 somehost exit 5$p
> + r=$?
> + if [ $r -ne 5$p ]; then
> + fail "ssh failed with trusted cert in config in protocol $p"
> + fi
> +done
> +
> +#next, using an agent in combination with the keys
> +SSH_AUTH_SOCK=/nonexistent ${SSHADD} -l > /dev/null 2>&1
> +if [ $? -ne 2 ]; then
> + fatal "ssh-add -l did not fail with exit code 2"
> +fi
> +
> +trace "start agent"
> +eval `${SSHAGENT} -s` > /dev/null
> +r=$?
> +if [ $r -ne 0 ]; then
> + fatal "could not start ssh-agent: exit code $r"
> +fi
> +
> +# add private keys to agent
> +${SSHADD} -k $OBJ/user_key2 > /dev/null 2>&1
> +if [ $? -ne 0 ]; then
> + fatal "ssh-add did not succeed with exit code 0"
> +fi
> +${SSHADD} -k $OBJ/user_key1 > /dev/null 2>&1
> +if [ $? -ne 0 ]; then
> + fatal "ssh-add did not succeed with exit code 0"
> +fi
> +
> +# try ssh with the agent and certificates
> +# note: ssh agent only uses certificates in protocol 2
> +opts="-F $OBJ/ssh_proxy"
> +# with no certificates, shoud fail
> +${SSH} -2 $opts somehost exit 52
> +if [ $? -eq 52 ]; then
> + fail "ssh connect with agent in protocol 2 succeeded with no cert"
> +fi
> +
> +#with an untrusted certificate, should fail
> +opts="$opts -z $OBJ/cert_user_key1_2.pub"
> +${SSH} -2 $opts somehost exit 52
> +if [ $? -eq 52 ]; then
> + fail "ssh connect with agent in protocol 2 succeeded with bad cert"
> +fi
> +
> +#with an additional trusted certificate, should succeed
> +opts="$opts -z $OBJ/cert_user_key1_1.pub"
> +${SSH} -2 $opts somehost exit 52
> +if [ $? -ne 52 ]; then
> + fail "ssh connect with agent in protocol 2 failed with good cert"
> +fi
> +
> +trace "kill agent"
> +${SSHAGENT} -k > /dev/null
> +
> +#cleanup
> +rm -f $OBJ/user_ca_key* $OBJ/user_key*
> +rm -f $OBJ/cert_user_key*
> diff --git a/ssh.1 b/ssh.1
> index 2ea0a20..76a9459 100644
> --- a/ssh.1
> +++ b/ssh.1
> @@ -63,6 +63,7 @@
> .Op Fl S Ar ctl_path
> .Op Fl W Ar host : Ns Ar port
> .Op Fl w Ar local_tun Ns Op : Ns Ar remote_tun
> +.Op Fl z Ar certificate_file
> .Oo Ar user Ns @ Oc Ns Ar hostname
> .Op Ar command
> .Ek
> @@ -468,6 +469,7 @@ For full details of the options listed below, and their possible values, see
> .It CanonicalizeHostname
> .It CanonicalizeMaxDots
> .It CanonicalizePermittedCNAMEs
> +.It CertificateFile
> .It ChallengeResponseAuthentication
> .It CheckHostIP
> .It Cipher
> @@ -768,6 +770,21 @@ Send log information using the
> .Xr syslog 3
> system module.
> By default this information is sent to stderr.
> +.It Fl z Ar certificate_file
> +Selects a file from which certificate information is loaded for public
> +key authentication. For the certificate to be signed, the private key
> +corresponding to
> +.Ar certificate_file
> +must also be provided for authentication, whether through
> +.Xr ssh_agent 1 .
> +or through an
> +.Ar identity_file
> +specified on the command line or in configuration files.
> +Certificate files may also be specified on a per-host basis in
> +the configuration file. It is possible to have multiple
> +.Fl z
> +options (and multiple certificates specified in
> +configuration files).
> .El
> .Pp
> .Nm
> diff --git a/ssh.c b/ssh.c
> index 3239108..e01790a 100644
> --- a/ssh.c
> +++ b/ssh.c
> @@ -207,7 +207,8 @@ usage(void)
> " [-O ctl_cmd] [-o option] [-p port]\n"
> " [-Q cipher | cipher-auth | mac | kex | key]\n"
> " [-R address] [-S ctl_path] [-W host:port]\n"
> -" [-w local_tun[:remote_tun]] [user@]hostname [command]\n"
> +" [-w local_tun[:remote_tun]] [-z certificate_file]\n"
> +" [user@]hostname [command]\n"
> );
> exit(255);
> }
> @@ -215,6 +216,7 @@ usage(void)
> static int ssh_session(void);
> static int ssh_session2(void);
> static void load_public_identity_files(void);
> +static void load_certificate_files(void);
> static void main_sigchld_handler(int);
>
> /* from muxclient.c */
> @@ -595,7 +597,7 @@ main(int ac, char **av)
>
> again:
> while ((opt = getopt(ac, av, "1246ab:c:e:fgi:kl:m:no:p:qstvx"
> - "ACD:E:F:GI:KL:MNO:PQ:R:S:TVw:W:XYy")) != -1) {
> + "ACD:E:F:GI:KL:MNO:PQ:R:S:TVw:W:XYyz:")) != -1) {
> switch (opt) {
> case '1':
> options.protocol = SSH_PROTO_1;
> @@ -906,6 +908,9 @@ main(int ac, char **av)
> case 'F':
> config = optarg;
> break;
> + case 'z':
> + add_certificate_file(&options, NULL, optarg, 1);
> + break;
> default:
> usage();
> }
> @@ -1013,6 +1018,9 @@ main(int ac, char **av)
> options.hostname = xstrdup(host);
> }
>
> + /* If the user has specified certificate(s), load it now. */
> + load_certificate_files();
> +
> /* If canonicalization requested then try to apply it */
> lowercase(host);
> if (options.canonicalize_hostname != SSH_CANONICALISE_NO)
> @@ -1353,6 +1361,13 @@ main(int ac, char **av)
> }
> }
>
> + for (i = 0; i < options.num_certificate_files; i++) {
> + free(options.certificate_files[i]);
> + options.certificate_files[i] = NULL;
> + }
> +
> +
> +
> exit_status = compat20 ? ssh_session2() : ssh_session();
> packet_close();
>
> @@ -1938,6 +1953,72 @@ ssh_session2(void)
> options.escape_char : SSH_ESCAPECHAR_NONE, id);
> }
>
> +/* Load certificate file(s) specified in options. */
> +static void
> +load_certificate_files(void)
> +{
> + char *filename, *cp, thishost[NI_MAXHOST];
> + char *pwdir = NULL, *pwname = NULL;
> + struct passwd *pw;
> + int i, n_ids;
> + struct sshkey *cert;
> + char *certificate_files[SSH_MAX_CERTIFICATE_FILES];
> + struct sshkey *certificates[SSH_MAX_CERTIFICATE_FILES];
> +
> + n_ids = 0;
> + memset(certificate_files, 0, sizeof(certificate_files));
> + memset(certificates, 0, sizeof(certificates));
> +
> + if ((pw = getpwuid(original_real_uid)) == NULL)
> + fatal("load_certificate_files: getpwuid failed");
> + pwname = xstrdup(pw->pw_name);
> + pwdir = xstrdup(pw->pw_dir);
> + if (gethostname(thishost, sizeof(thishost)) == -1)
> + fatal("load_certificate_files: gethostname: %s",
> + strerror(errno));
> +
> + if (options.num_certificate_files > SSH_MAX_CERTIFICATE_FILES)
> + fatal("load_certificate_files: too many certificates");
> + for (i = 0; i < options.num_certificate_files; i++) {
> + cp = tilde_expand_filename(options.certificate_files[i],
> + original_real_uid);
> + filename = percent_expand(cp, "d", pwdir,
> + "u", pwname, "l", thishost, "h", host,
> + "r", options.user, (char *)NULL);
> + free(cp);
> +
> + cert = key_load_public(filename, NULL);
> + debug("certificate file %s type %d", filename,
> + cert ? cert->type : -1);
> + free(options.certificate_files[i]);
> + if (cert == NULL) {
> + free(filename);
> + continue;
> + }
> + if (!key_is_cert(cert)) {
> + debug("%s: key %s type %s is not a certificate",
> + __func__, filename, key_type(cert));
> + key_free(cert);
> + free(filename);
> + continue;
> + }
> +
> + certificate_files[n_ids] = filename;
> + certificates[n_ids] = cert;
> + ++n_ids;
> + }
> + options.num_certificate_files = n_ids;
> + memcpy(options.certificate_files, certificate_files, sizeof(certificate_files));
> + memcpy(options.certificates, certificates, sizeof(certificates));
> +
> + explicit_bzero(pwname, strlen(pwname));
> + free(pwname);
> + explicit_bzero(pwdir, strlen(pwdir));
> + free(pwdir);
> +}
> +
> +
> +
> static void
> load_public_identity_files(void)
> {
> diff --git a/ssh.h b/ssh.h
> index 4f8da5c..8fb7ba3 100644
> --- a/ssh.h
> +++ b/ssh.h
> @@ -19,6 +19,13 @@
> #define SSH_DEFAULT_PORT 22
>
> /*
> + * Maximum number of certificate files that can be specified
> + * in configuration files or on the command line.
> + */
> +#define SSH_MAX_CERTIFICATE_FILES 100
> +
> +
> +/*
> * Maximum number of RSA authentication identity files that can be specified
> * in configuration files or on the command line.
> */
> diff --git a/ssh_config.5 b/ssh_config.5
> index e514398..17741b7 100644
> --- a/ssh_config.5
> +++ b/ssh_config.5
> @@ -325,6 +325,34 @@ to be canonicalized to names in the
> or
> .Dq *.c.example.com
> domains.
> +.It Cm CertificateFile
> +Specifies a file from which the user's certificate is read.
> +A corresponding private key must be provided separately in order
> +to use this certificate.
> +.Xr ssh 1
> +will attempt to use private keys provided as identity files
> +or in the agent for such authentication.
> +.Pp
> +The file name may use the tilde
> +syntax to refer to a user's home directory or one of the following
> +escape characters:
> +.Ql %d
> +(local user's home directory),
> +.Ql %u
> +(local user name),
> +.Ql %l
> +(local host name),
> +.Ql %h
> +(remote host name) or
> +.Ql %r
> +(remote user name).
> +.Pp
> +It is possible to have multiple certificate files specified in
> +configuration files; these certificates will be tried in sequence.
> +Multiple
> +.Cm CertificateFile
> +directives will add to the list of certificates used for
> +authentication.
> .It Cm ChallengeResponseAuthentication
> Specifies whether to use challenge-response authentication.
> The argument to this keyword must be
> @@ -911,6 +939,11 @@ differs from that of other configuration directives).
> may be used in conjunction with
> .Cm IdentitiesOnly
> to select which identities in an agent are offered during authentication.
> +.Cm IdentityFile
> +may also be used in conjunction with
> +.Cm CertificateFile
> +in order to provide any certificate also needed for authentication with
> +the identity.
> .It Cm IgnoreUnknown
> Specifies a pattern-list of unknown options to be ignored if they are
> encountered in configuration parsing.
> diff --git a/sshconnect2.c b/sshconnect2.c
> index 34dbf9a..fb24b5e 100644
> --- a/sshconnect2.c
> +++ b/sshconnect2.c
> @@ -1016,6 +1016,7 @@ sign_and_send_pubkey(Authctxt *authctxt, Identity *id)
> u_int skip = 0;
> int ret = -1;
> int have_sig = 1;
> + int i;
> char *fp;
>
> if ((fp = sshkey_fingerprint(id->key, options.fingerprint_hash,
> @@ -1053,6 +1054,33 @@ sign_and_send_pubkey(Authctxt *authctxt, Identity *id)
> }
> buffer_put_string(&b, blob, bloblen);
>
> + /* If the key is an input certificate, sign its private key instead.
> + * If no such private key exists, return failure and continue with
> + * other methods of authentication.
> + * Else, just continue with the normal signing process. */
> + if (key_is_cert(id->key)) {
> + for (i = 0; i < options.num_certificate_files; i++) {
> + if (key_equal(id->key, options.certificates[i])) {
> + Identity *id2;
> + int matched = 0;
> + TAILQ_FOREACH(id2, &authctxt->keys, next) {
> + if (sshkey_equal_public(id->key, id2->key) &&
> + id->key->type != id2->key->type) {
> + id = id2;
> + matched = 1;
> + break;
> + }
> + }
> + if (!matched) {
> + free(blob);
> + buffer_free(&b);
> + return 0;
> + }
> + break;
> + }
> + }
> + }
> +
> /* generate signature */
> ret = identity_sign(id, &signature, &slen,
> buffer_ptr(&b), buffer_len(&b), datafellows);
> @@ -1189,9 +1217,11 @@ load_identity_file(char *filename, int userprovided)
>
> /*
> * try keys in the following order:
> - * 1. agent keys that are found in the config file
> - * 2. other agent keys
> - * 3. keys that are only listed in the config file
> + * 1. certificates listed in the config file
> + * 2. other input certificates
> + * 3. agent keys that are found in the config file
> + * 4. other agent keys
> + * 5. keys that are only listed in the config file
> */
> static void
> pubkey_prepare(Authctxt *authctxt)
> @@ -1245,6 +1275,17 @@ pubkey_prepare(Authctxt *authctxt)
> free(id);
> }
> }
> + /* list of certificates specified by user */
> + for (i = 0; i < options.num_certificate_files; i++) {
> + key = options.certificates[i];
> + if (!key_is_cert(key))
> + continue;
> + id = xcalloc(1, sizeof(*id));
> + id->key = key;
> + id->filename = xstrdup(options.certificate_files[i]);
> + id->userprovided = options.certificate_file_userprovided[i];
> + TAILQ_INSERT_TAIL(preferred, id, next);
> + }
> /* list of keys supported by the agent */
> if ((r = ssh_get_authentication_socket(&agent_fd)) != 0) {
> if (r != SSH_ERR_AGENT_NOT_PRESENT)
> --
> 1.9.1
>
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