From: Sören Tempel Subject: Re: [PATCH] relayd client certificate validation again To: tech@openbsd.org Cc: markus.l2ll@gmail.com, rivo@elnit.ee, brian@planetunix.net Date: Mon, 30 Sep 2024 18:57:26 +0200 Hello! Is there a reason why this patch never got a review? The feature (TLS client certificate validation within relayd) seems to be requested frequently [1]. I just came across this while looking into working on such a patch myself. Is the feature not deemed useful, or is the patch not in a good shape? If the latter is the case, I would be willing to revise the patch. I would also be fine with just implementing the validation part without adding the capability to forward the validated certificate, which should shrink the patchset a bit. Cheers Sören [1]: https://marc.info/?t=154295268000001&r=1&w=2 Markus Läll wrote: > Hi, we've got the patch ready for client certificate validation, cc'ing > related people. > > The patch adds two features: > 1. client certificate validation itself > 2. passing on certificate and select fields in HTTP headers > > > ## Brief description of client certificates (for whoever else is reading) > > Client certificates, also known as mutual authentication, are the reverse > to TLS server certificates (like letsencrypt) where the server > authenticates the user instead of the other way around. > > In principle client certificates work as follows: > - the server has keypair and a CA certificate created from this keypair > - the user has a keypair and submits their public key for certification (to > being signed by the CA) > - the server (relayd) has the CA certificate configured as 'client ca > "/path/to/ca.pem"' > - the user provides their certificate when connecting, the provided > certificate is validated against the CA certificate. > > How this is set up in practice is up to whoever implements the > infrastructure. Client certificates can be installed to operating systems' > certificate stores (Windows, macOS) where browsers can use them, or into > browsers own certificate stores (Firefox has its own), or specified on the > command line (curl, wget) etc. > > > ## Configuration > > To turn on client certificate validation add > > tls { client ca "/path/to/ca-cert.pem" } > > to relayd.conf. > > Add "optional" flag to make the certificate not required: > > tls { client ca "/path/to/cert.pem" optional } > > With "optional" relayd will succeed in the TLS handshake when no client > certificate is provided. But if a certificate *is* provided then it *must* > validate with the configured CA, otherwise the TLS handshake fails. > > > ## Pass certificate on in HTTP header > > To pass on the certificate in an url-encoded PEM: > > match header set "ANY_HEADER_NAME" value "$CLIENT_CERT_CHAIN" > > With this configuration the downstream can inspect the known-to-be-valid > certificate further (e.g extract identity or other info from x509 > extensions). > > There was discussion privately on is there any standard for putting > certificates in HTTP headers, repeating the reply here as well: > > There appears to be no standard, but this is how other HTTP servers do it: > - nginx urlencodes the PEM file with $ssl_client_escaped_cert[1] (this is > what is done in this patch too). There is also the $ssl_client_cert > variable which adds a tab to each next new line, but this way of doing > multiline HTTP headers is deprecated[2]. There is also > $ssl_client_raw_cert, but the raw multiline PEM is invalid HTTP header; > - envoy also urlencodes the PEM[3]; > - haproxy has only the binary DER, but base64 encoding it like > %[ssl_c_der,base64]) should result in PEM with no newlines and no headers; > - apache has the %{SSL_CLIENT_CERT} with raw (multiline) PEM[4], which is > invalid in HTTP headers, but this can be processed with the escape > function[5], something like "expr=3D %{escape:SSL_CLIENT_CERT}" > > [1] > https://nginx.org/en/docs/http/ngx_http_ssl_module.html#var_ssl_client_esca= > ped_cert > [2] https://tools.ietf.org/html/rfc7230#section-3.2.4 > [3] > https://www.envoyproxy.io/docs/envoy/latest/configuration/http/http_conn_ma= > n/headers#x-forwarded-client-cert > [4] https://httpd.apache.org/docs/current/mod/mod_ssl.html#envvars > [5] https://httpd.apache.org/docs/current/expr.html#functions > > In addition to extracting the entire certificate, subject and issuer can be > put to HTTP headers too for convenience: > > match header set "CS_SUBJECT" value "$CLIENT_CERT_SUBJECT" > match header set "CS_ISSUER" value "$CLIENT_CERT_ISSUER" > > > > --=20 > Markus L=C3=A4ll > > On Thu, Dec 16, 2021 at 11:23 PM rivo nurges wrote: > > > Hi! > > > > Here comes the support for relayd client certificate validation. > > Full certificate chain, subject and issuer can be passed over in http > > headers. > > It supports mandatory validation and optional validation(if client chooses > > to > > provide certificate it will be validated). > > > > Part of my sample config. > > > > http protocol test { > > match header set "CS_SUBJECT" value "$CLIENT_CERT_SUBJECT" > > match header set "CS_ISSUER" value "$CLIENT_CERT_ISSUER" > > match header set "CS_CERT" value "$CLIENT_CERT_CHAIN" > > pass > > tls {client ca "/tmp/easyrsa3/pki/ca.crt" optional } > > } > > > > This uses code from the patches submitted by Ashe Connor. > > > > Rivo > > > > diff refs/heads/master refs/heads/relay-clc3 > > blob - a2f1c130d6b45e3082048218c11537dca485998a > > blob + 5070a7d48f58403f53d818231e1676db749aa9d7 > > --- usr.sbin/relayd/config.c > > +++ usr.sbin/relayd/config.c > > @@ -954,6 +954,15 @@ config_setrelay(struct relayd *env, struct relay *rl= > ay > > rlay->rl_conf.name); > > return (-1); > > } > > + if (rlay->rl_tls_client_ca_fd !=3D -1 && > > + config_setrelayfd(ps, id, n, 0, > > + rlay->rl_conf.id, > > RELAY_FD_CLIENTCACERT, > > + rlay->rl_tls_client_ca_fd) =3D=3D -1)= > { > > + log_warn("%s: fd passing failed > > for " > > + "`%s'", __func__, > > + rlay->rl_conf.name); > > + return (-1); > > + } > > /* Prevent fd exhaustion in the parent. */ > > if (proc_flush_imsg(ps, id, n) =3D=3D -1)= > { > > log_warn("%s: failed to flush " > > @@ -987,6 +996,10 @@ config_setrelay(struct relayd *env, struct relay *rl= > ay > > close(rlay->rl_s); > > rlay->rl_s =3D -1; > > } > > + if (rlay->rl_tls_client_ca_fd !=3D -1) { > > + close(rlay->rl_tls_client_ca_fd); > > + rlay->rl_tls_client_ca_fd =3D -1; > > + } > > if (rlay->rl_tls_cacert_fd !=3D -1) { > > close(rlay->rl_tls_cacert_fd); > > rlay->rl_tls_cacert_fd =3D -1; > > @@ -1012,6 +1025,10 @@ config_setrelay(struct relayd *env, struct relay > > *rlay > > cert->cert_ocsp_fd =3D -1; > > } > > } > > + if (rlay->rl_tls_client_ca_fd !=3D -1) { > > + close(rlay->rl_tls_client_ca_fd); > > + rlay->rl_tls_client_ca_fd =3D -1; > > + } > > > > return (0); > > } > > @@ -1034,6 +1051,7 @@ config_getrelay(struct relayd *env, struct imsg > > *imsg) > > rlay->rl_s =3D imsg->fd; > > rlay->rl_tls_ca_fd =3D -1; > > rlay->rl_tls_cacert_fd =3D -1; > > + rlay->rl_tls_client_ca_fd =3D -1; > > > > if (ps->ps_what[privsep_process] & CONFIG_PROTOS) { > > if (rlay->rl_conf.proto =3D=3D EMPTY_ID) > > @@ -1163,6 +1181,9 @@ config_getrelayfd(struct relayd *env, struct imsg > > *ims > > case RELAY_FD_CAFILE: > > rlay->rl_tls_cacert_fd =3D imsg->fd; > > break; > > + case RELAY_FD_CLIENTCACERT: > > + rlay->rl_tls_client_ca_fd =3D imsg->fd; > > + break; > > } > > > > DPRINTF("%s: %s %d received relay fd %d type %d for relay %s", > > __func__, > > blob - 22beb857229a16e5b2c17a25a2944231d41e7e08 > > blob + fe5e8ff4dfed10e8f09e3226bdfe33f8bc031c8e > > --- usr.sbin/relayd/parse.y > > +++ usr.sbin/relayd/parse.y > > @@ -172,14 +172,14 @@ typedef struct { > > %token CODE COOKIE DEMOTE DIGEST DISABLE ERROR EXPECT PASS BLOCK > > EXTERNAL > > %token FILENAME FORWARD FROM HASH HEADER HEADERLEN HOST HTTP ICMP > > INCLUDE INET > > %token INET6 INTERFACE INTERVAL IP KEYPAIR LABEL LISTEN VALUE > > LOADBALANCE LOG > > -%token LOOKUP METHOD MODE NAT NO DESTINATION NODELAY NOTHING ON PARENT > > PATH > > +%token LOOKUP METHOD MODE NAT NO DESTINATION NODELAY NOTHING ON OPTIONAL > > PARENT PATH > > %token PFTAG PORT PREFORK PRIORITY PROTO QUERYSTR REAL REDIRECT > > RELAY REMOVE > > %token REQUEST RESPONSE RETRY QUICK RETURN ROUNDROBIN ROUTE SACK > > SCRIPT SEND > > %token SESSION SOCKET SPLICE SSL STICKYADDR STRIP STYLE TABLE TAG > > TAGGED TCP > > %token TIMEOUT TLS TO ROUTER RTLABEL TRANSPARENT URL WITH TTL > > RTABLE > > %token MATCH PARAMS RANDOM LEASTSTATES SRCHASH KEY CERTIFICATE > > PASSWORD ECDHE > > %token EDH TICKETS CONNECTION CONNECTIONS CONTEXT ERRORS STATE > > CHANGES CHECKS > > -%token WEBSOCKETS > > +%token WEBSOCKETS CLIENT > > %token STRING > > %token NUMBER > > %type context hostname interface table value path > > @@ -188,6 +188,7 @@ typedef struct { > > %type opttls opttlsclient > > %type redirect_proto relay_proto match > > %type action ruleaf key_option > > +%type clientcaopt > > %type port > > %type host > > %type address rulesrc ruledst addrprefix > > @@ -244,6 +245,10 @@ opttlsclient : /*empty*/ { $$ =3D 0; } > > | WITH ssltls { $$ =3D 1; } > > ; > > > > +clientcaopt : /*empty*/ { $$ =3D 0; } > > + | OPTIONAL { $$ =3D 1; } > > + ; > > + > > http_type : HTTP { $$ =3D 0; } > > | STRING { > > if (strcmp("https", $1) =3D=3D 0) { > > @@ -1353,6 +1358,19 @@ tlsflags : SESSION TICKETS { proto->tickets =3D 1;= > } > > name->name =3D $2; > > TAILQ_INSERT_TAIL(&proto->tlscerts, name, entry); > > } > > + | CLIENT CA STRING clientcaopt { > > + if (strlcpy(proto->tlsclientca, $3, > > + sizeof(proto->tlsclientca)) >=3D > > + sizeof(proto->tlsclientca)) { > > + yyerror("tlsclientca truncated"); > > + free($3); > > + YYERROR; > > + } > > + if ($4) { > > + proto->tlsflags |=3D > > TLSFLAG_CLIENT_OPTIONAL; > > + } > > + free($3); > > + } > > | NO flag { proto->tlsflags &=3D > > ~($2); } > > | flag { proto->tlsflags |=3D $1= > ; } > > ; > > @@ -1824,6 +1842,7 @@ relay : RELAY STRING { > > r->rl_conf.dstretry =3D 0; > > r->rl_tls_ca_fd =3D -1; > > r->rl_tls_cacert_fd =3D -1; > > + r->rl_tls_client_ca_fd =3D -1; > > TAILQ_INIT(&r->rl_tables); > > if (last_relay_id =3D=3D INT_MAX) { > > yyerror("too many relays defined"); > > @@ -2413,6 +2432,7 @@ lookup(char *s) > > { "check", CHECK }, > > { "checks", CHECKS }, > > { "ciphers", CIPHERS }, > > + { "client", CLIENT }, > > { "code", CODE }, > > { "connection", CONNECTION }, > > { "context", CONTEXT }, > > @@ -2458,6 +2478,7 @@ lookup(char *s) > > { "nodelay", NODELAY }, > > { "nothing", NOTHING }, > > { "on", ON }, > > + { "optional", OPTIONAL }, > > { "params", PARAMS }, > > { "parent", PARENT }, > > { "pass", PASS }, > > @@ -3399,6 +3420,7 @@ relay_inherit(struct relay *ra, struct relay *rb) > > if (!(rb->rl_conf.flags & F_TLS)) { > > rb->rl_tls_cacert_fd =3D -1; > > rb->rl_tls_ca_fd =3D -1; > > + rb->rl_tls_client_ca_fd =3D -1; > > } > > TAILQ_INIT(&rb->rl_tables); > > > > blob - da4a1aa0cc1158b22506c6d81e4d36b8810c025c > > blob + 2d16b9d91e594a06d4b1b2bfc791c7f0c861fc57 > > --- usr.sbin/relayd/relay.c > > +++ usr.sbin/relayd/relay.c > > @@ -2255,6 +2255,30 @@ relay_tls_ctx_create(struct relay *rlay) > > } > > rlay->rl_tls_cacert_fd =3D -1; > > > > + if (rlay->rl_tls_client_ca_fd !=3D -1) { > > + if ((buf =3D relay_load_fd(rlay->rl_tls_client_ca= > _fd, > > + &len)) =3D=3D > > + NULL) { > > + log_warn( > > + "failed to read tls client CA > > certificate"); > > + goto err; > > + } > > + > > + if (tls_config_set_ca_mem(tls_cfg, buf, len) !=3D= > 0) > > { > > + log_warnx( > > + "failed to set tls client CA cert: %s= > ", > > + tls_config_error(tls_cfg)); > > + goto err; > > + } > > + purge_key(&buf, len); > > + > > + if (rlay->rl_proto->tlsflags & > > TLSFLAG_CLIENT_OPTIONAL) > > + tls_config_verify_client_optional(tls_cfg= > ); > > + else > > + tls_config_verify_client(tls_cfg); > > + } > > + rlay->rl_tls_client_ca_fd =3D -1; > > + > > tls =3D tls_server(); > > if (tls =3D=3D NULL) { > > log_warnx("unable to allocate TLS context"); > > blob - d493c238813cfc692d83f65a88d4556b2fa35b0f > > blob + 58ba35c16ea8d80b36796d977ad7920d3bed3a9c > > --- usr.sbin/relayd/relay_http.c > > +++ usr.sbin/relayd/relay_http.c > > @@ -78,6 +78,7 @@ int relay_match_actions(struct > > ctl_relay_event *, > > struct relay_table **); > > void relay_httpdesc_free(struct http_descriptor *); > > char * server_root_strip(char *, int); > > +char *url_encode(const char *); > > > > static struct relayd *env =3D NULL; > > > > @@ -1279,7 +1280,32 @@ relay_expand_http(struct ctl_relay_event *cre, char > > *v > > if (expand_string(buf, len, "$TIMEOUT", ibuf) !=3D 0) > > return (NULL); > > } > > - > > + if (strstr(val, "$CLIENT_CERT_") !=3D NULL && > > tls_peer_cert_provided(cre->tls)) { > > + if (strstr(val, "$CLIENT_CERT_SUBJECT") !=3D NULL) { > > + if (expand_string(buf, len, > > + "$CLIENT_CERT_SUBJECT", > > tls_peer_cert_subject(cre->tls)) !=3D 0) > > + return (NULL); > > + } > > + if (strstr(val, "$CLIENT_CERT_ISSUER") !=3D NULL) { > > + if (expand_string(buf, len, > > + "$CLIENT_CERT_ISSUER", > > tls_peer_cert_issuer(cre->tls)) !=3D 0) > > + return (NULL); > > + } > > + if (strstr(val, "$CLIENT_CERT_CHAIN") !=3D NULL) { > > + const char *pem; > > + char *cbuf; > > + size_t plen; > > + pem =3D tls_peer_cert_chain_pem(cre->tls, &plen); > > + cbuf =3D malloc(plen); > > + sprintf(cbuf, "%.*s", (int)plen - 1, pem); > > + if (expand_string(buf, len, > > + "$CLIENT_CERT_CHAIN", url_encode(cbuf)) !=3D = > 0) { > > + free(cbuf); > > + return (NULL); > > + } else > > + free(cbuf); > > + } > > + } > > return (buf); > > } > > > > @@ -2045,3 +2071,27 @@ server_root_strip(char *path, int n) > > return (path); > > } > > > > +char * > > +url_encode(const char *src) > > +{ > > + static char hex[] =3D "0123456789ABCDEF"; > > + char *dp, *dst; > > + unsigned char c; > > + > > + /* We need 3 times the memory if every letter is encoded. */ > > + if ((dst =3D calloc(3, strlen(src) + 1)) =3D=3D NULL) > > + return (NULL); > > + > > + for (dp =3D dst; *src !=3D 0; src++) { > > + c =3D (unsigned char) *src; > > + if (c =3D=3D ' ' || c =3D=3D '#' || c =3D=3D '%' || c =3D= > =3D '?' || c =3D=3D > > '"' || > > + c =3D=3D '&' || c =3D=3D '<' || c <=3D 0x1f || c >=3D= > 0x7f) { > > + *dp++ =3D '%'; > > + *dp++ =3D '%'; > > + *dp++ =3D hex[c >> 4]; > > + *dp++ =3D hex[c & 0x0f]; > > + } else > > + *dp++ =3D *src; > > + } > > + return (dst); > > +} > > blob - 54e26e646fae5804e66d2d3cfeba68e06914ab2b > > blob + cd99c21d7cdaf9fc5fdc33e5a0ad886afaa9b889 > > --- usr.sbin/relayd/relayd.c > > +++ usr.sbin/relayd/relayd.c > > @@ -1360,6 +1360,15 @@ relay_load_certfiles(struct relayd *env, struct > > relay > > if ((rlay->rl_conf.flags & F_TLS) =3D=3D 0) > > return (0); > > > > + if (strlen(proto->tlsclientca) && > > + rlay->rl_tls_client_ca_fd =3D=3D -1) { > > + if ((rlay->rl_tls_client_ca_fd =3D > > + open(proto->tlsclientca, O_RDONLY)) =3D=3D -1) > > + return (-1); > > + log_debug("%s: using client ca %s", __func__, > > + proto->tlsclientca); > > + } > > + > > if (name =3D=3D NULL && > > print_host(&rlay->rl_conf.ss, hbuf, sizeof(hbuf)) =3D=3D NULL) > > goto fail; > > blob - cecbae71f87e603b3e30d4c0114bf1c60a82b52a > > blob + cfb7a314811730723449a5109d500014711db3ae > > --- usr.sbin/relayd/relayd.conf.5 > > +++ usr.sbin/relayd/relayd.conf.5 > > @@ -948,6 +948,13 @@ will be used (strong crypto cipher suites without an= > on > > See the CIPHERS section of > > .Xr openssl 1 > > for information about SSL/TLS cipher suites and preference lists. > > +.It Ic client ca Ar path Op optional > > +Require TLS client certificates whose authenticity can be verified > > +against the CA certificate(s) in the specified file in order to > > +proceed beyond the TLS handshake. > > +If the > > +.Ic optional > > +keyword is present, the certificate is verified only if presented. > > .It Ic client-renegotiation > > Allow client-initiated renegotiation. > > To mitigate a potential DoS risk, > > @@ -1361,6 +1368,12 @@ The value string may contain predefined macros that > > wi > > at runtime: > > .Pp > > .Bl -tag -width $SERVER_ADDR -offset indent -compact > > +.It Ic $CLIENT_CERT_CHAIN > > +The certificate chain of the client certificate. > > +.It Ic $CLIENT_CERT_ISSUER > > +The issuer of the client certificate. > > +.It Ic $CLIENT_CERT_SUBJECT > > +The subject of the client certificate. > > .It Ic $HOST > > The Host header's value of the relay. > > .It Ic $REMOTE_ADDR > > blob - 2236d140f7e6b9477bac401cbcdd559db171680b > > blob + 2a1166599bfd57b0682c4d4bacd15d340ff9b5ad > > --- usr.sbin/relayd/relayd.h > > +++ usr.sbin/relayd/relayd.h > > @@ -139,11 +139,12 @@ struct ctl_relaytable { > > }; > > > > enum fd_type { > > - RELAY_FD_CERT =3D 1, > > - RELAY_FD_CACERT =3D 2, > > - RELAY_FD_CAFILE =3D 3, > > - RELAY_FD_KEY =3D 4, > > - RELAY_FD_OCSP =3D 5 > > + RELAY_FD_CERT =3D 1, > > + RELAY_FD_CACERT =3D 2, > > + RELAY_FD_CAFILE =3D 3, > > + RELAY_FD_KEY =3D 4, > > + RELAY_FD_OCSP =3D 5, > > + RELAY_FD_CLIENTCACERT =3D 6 > > }; > > > > struct ctl_relayfd { > > @@ -403,6 +404,7 @@ union hashkey { > > #define F_TLSINSPECT 0x04000000 > > #define F_HASHKEY 0x08000000 > > #define F_AGENTX_TRAPONLY 0x10000000 > > +#define F_TLSVERIFY 0x20000000 > > > > #define F_BITS > > \ > > "\10\01DISABLE\02BACKUP\03USED\04DOWN\05ADD\06DEL\07CHANGED" \ > > @@ -703,6 +705,7 @@ TAILQ_HEAD(relay_rules, relay_rule); > > #define TLSFLAG_VERSION 0x1f > > #define TLSFLAG_CIPHER_SERVER_PREF 0x20 > > #define TLSFLAG_CLIENT_RENEG 0x40 > > +#define TLSFLAG_CLIENT_OPTIONAL 0x80 > > #define TLSFLAG_DEFAULT \ > > (TLSFLAG_TLSV1_2|TLSFLAG_TLSV1_3|TLSFLAG_CIPHER_SERVER_PREF) > > > > @@ -746,6 +749,7 @@ struct protocol { > > char tlscacert[PATH_MAX]; > > char tlscakey[PATH_MAX]; > > char *tlscapass; > > + char tlsclientca[PATH_MAX]; > > struct keynamelist tlscerts; > > char name[MAX_NAME_SIZE]; > > int tickets; > > @@ -835,6 +839,7 @@ struct relay { > > > > int rl_tls_ca_fd; > > int rl_tls_cacert_fd; > > + int rl_tls_client_ca_fd; > > EVP_PKEY *rl_tls_pkey; > > X509 *rl_tls_cacertx509; > > char *rl_tls_cakey;