Add mod_session support

By setting GssapiUseSessions we enable the module to store a bearer
token with the user and gss names in the client, this way we can allow
clients to perform authentication once but then remain authenticaed
for the duration of the session or until the original credentials expire.

The Secure cookie used to store the token is encrypted using a randomly
generated AES key at process startup. This means multiple apache servers
will not be able to use the same cookie, however the client will reauth
transparently if the cookie cannot be read.

Author: simo5

src/Makefile.am

@@ -1,5 +1,5 @@
 all-local:
-	@APXS@ -c ${LIBS} ${CFLAGS} mod_auth_gssapi.c
+	@APXS@ -c ${LIBS} ${CFLAGS} mod_auth_gssapi.c sessions.c crypto.c
 
 install-exec-local:
 	if test ! -d ${APXS_LIBEXECDIR}; then mkdir -p ${APXS_LIBEXECDIR}; fi

src/crypto.c

@@ -0,0 +1,210 @@
+/* Copyright (C) 2014 mod_auth_gssapi authors - See COPYING for (C) terms */
+
+#include <openssl/evp.h>
+#include <openssl/hmac.h>
+#include <openssl/rand.h>
+#include <stdbool.h>
+#include "crypto.h"
+
+struct seal_key {
+    const EVP_CIPHER *cipher;
+    const EVP_MD *md;
+    unsigned char *ekey;
+    unsigned char *hkey;
+};
+
+apr_status_t SEAL_KEY_CREATE(struct seal_key **skey)
+{
+    struct seal_key *n;
+    int ret;
+
+    n = calloc(1, sizeof(*n));
+    if (!n) return ENOMEM;
+
+    n->cipher = EVP_aes_128_cbc();
+    if (!n->cipher) {
+        free(n);
+        return EFAULT;
+    }
+
+    n->md = EVP_sha256();
+    if (!n->md) {
+        free(n);
+        return EFAULT;
+    }
+
+    n->ekey = malloc(n->cipher->key_len);
+    if (!n->ekey) {
+        free(n);
+        return ENOMEM;
+    }
+
+    n->hkey = malloc(n->cipher->key_len);
+    if (!n->hkey) {
+        free(n);
+        return ENOMEM;
+    }
+
+    ret = RAND_bytes(n->ekey, n->cipher->key_len);
+    if (ret == 0) {
+        free(n->ekey);
+        free(n->hkey);
+        free(n);
+        return EFAULT;
+    }
+
+    ret = RAND_bytes(n->hkey, n->cipher->key_len);
+    if (ret == 0) {
+        free(n->ekey);
+        free(n->hkey);
+        free(n);
+        return EFAULT;
+    }
+
+    *skey = n;
+    return 0;
+}
+
+apr_status_t SEAL_BUFFER(apr_pool_t *p, struct seal_key *skey,
+                         struct databuf *plain, struct databuf *cipher)
+{
+    apr_status_t err = EFAULT;
+    EVP_CIPHER_CTX ctx = { 0 };
+    HMAC_CTX hmac_ctx = { 0 };
+    uint8_t rbuf[16];
+    unsigned int len;
+    int outlen, totlen;
+    int ret;
+
+    EVP_CIPHER_CTX_init(&ctx);
+
+    /* confounder to avoid exposing random numbers directly to clients
+     * as IVs */
+    ret = RAND_bytes(rbuf, 16);
+    if (ret == 0) goto done;
+
+    if (cipher->length == 0) {
+        /* add space for confounder and padding and MAC */
+        cipher->length = (plain->length / 16 + 2) * 16;
+        cipher->value = apr_palloc(p, cipher->length + skey->md->md_size);
+        if (!cipher->value) {
+            err = ENOMEM;
+            goto done;
+        }
+    }
+
+    ret = EVP_EncryptInit_ex(&ctx, skey->cipher, NULL, skey->ekey, NULL);
+    if (ret == 0) goto done;
+    totlen = 0;
+
+    outlen = cipher->length;
+    ret = EVP_EncryptUpdate(&ctx, cipher->value, &outlen, rbuf, 16);
+    if (ret == 0) goto done;
+    totlen += outlen;
+
+    outlen = cipher->length - totlen;
+    ret = EVP_EncryptUpdate(&ctx, &cipher->value[totlen], &outlen,
+                            plain->value, plain->length);
+    if (ret == 0) goto done;
+    totlen += outlen;
+
+    outlen = cipher->length - totlen;
+    ret = EVP_EncryptFinal_ex(&ctx, &cipher->value[totlen], &outlen);
+    if (ret == 0) goto done;
+    totlen += outlen;
+
+    /* now MAC the buffer */
+    HMAC_CTX_init(&hmac_ctx);
+
+    ret = HMAC_Init_ex(&hmac_ctx, skey->hkey,
+                       skey->cipher->key_len, skey->md, NULL);
+    if (ret == 0) goto done;
+
+    ret = HMAC_Update(&hmac_ctx, cipher->value, totlen);
+    if (ret == 0) goto done;
+
+    ret = HMAC_Final(&hmac_ctx, &cipher->value[totlen], &len);
+    if (ret == 0) goto done;
+
+    cipher->length = totlen + len;
+    err = 0;
+
+done:
+    EVP_CIPHER_CTX_cleanup(&ctx);
+    HMAC_CTX_cleanup(&hmac_ctx);
+    return err;
+}
+
+apr_status_t UNSEAL_BUFFER(apr_pool_t *p, struct seal_key *skey,
+                           struct databuf *cipher, struct databuf *plain)
+{
+    apr_status_t err = EFAULT;
+    EVP_CIPHER_CTX ctx = { 0 };
+    HMAC_CTX hmac_ctx = { 0 };
+    unsigned char mac[skey->md->md_size];
+    unsigned int len;
+    int outlen, totlen;
+    volatile bool equal = true;
+    int ret, i;
+
+    /* check MAC first */
+    HMAC_CTX_init(&hmac_ctx);
+
+    ret = HMAC_Init_ex(&hmac_ctx, skey->hkey,
+                       skey->cipher->key_len, skey->md, NULL);
+    if (ret == 0) goto done;
+
+    cipher->length -= skey->md->md_size;
+
+    ret = HMAC_Update(&hmac_ctx, cipher->value, cipher->length);
+    if (ret == 0) goto done;
+
+    ret = HMAC_Final(&hmac_ctx, mac, &len);
+    if (ret == 0) goto done;
+
+    if (len != skey->md->md_size) goto done;
+    for (i = 0; i < skey->md->md_size; i++) {
+        if (cipher->value[cipher->length + i] != mac[i]) equal = false;
+        /* not breaking intentionally,
+         * or we would allow an oracle attack */
+    }
+    if (!equal) goto done;
+
+    EVP_CIPHER_CTX_init(&ctx);
+
+    if (plain->length == 0) {
+        plain->length = cipher->length;
+        plain->value = apr_palloc(p, plain->length);
+        if (!plain->value) {
+            err = ENOMEM;
+            goto done;
+        }
+    }
+
+    ret = EVP_DecryptInit_ex(&ctx, skey->cipher, NULL, skey->ekey, NULL);
+    if (ret == 0) goto done;
+
+    totlen = 0;
+    outlen = plain->length;
+    ret = EVP_DecryptUpdate(&ctx, plain->value, &outlen,
+                            cipher->value, cipher->length);
+    if (ret == 0) goto done;
+
+    totlen += outlen;
+    outlen = plain->length - totlen;
+    ret = EVP_DecryptFinal_ex(&ctx, plain->value, &outlen);
+    if (ret == 0) goto done;
+
+    totlen += outlen;
+    /* now remove the confounder */
+    totlen -= 16;
+    memmove(plain->value, plain->value + 16, totlen);
+
+    plain->length = totlen;
+    err = 0;
+
+done:
+    EVP_CIPHER_CTX_cleanup(&ctx);
+    HMAC_CTX_cleanup(&hmac_ctx);
+    return err;
+}

src/crypto.h

@@ -0,0 +1,17 @@
+/* Copyright (C) 2014 mod_auth_gssapi authors - See COPYING for (C) terms */
+
+#include <apr_errno.h>
+#include <apr_pools.h>
+
+struct seal_key;
+
+struct databuf {
+    unsigned char *value;
+    int length;
+};
+
+apr_status_t SEAL_KEY_CREATE(struct seal_key **skey);
+apr_status_t SEAL_BUFFER(apr_pool_t *p, struct seal_key *skey,
+                         struct databuf *plain, struct databuf *cipher);
+apr_status_t UNSEAL_BUFFER(apr_pool_t *p, struct seal_key *skey,
+                           struct databuf *cipher, struct databuf *plain);

src/mod_auth_gssapi.c

@@ -24,6 +24,7 @@
 
 #include "mod_auth_gssapi.h"
 
+
 module AP_MODULE_DECLARE_DATA auth_gssapi_module;
 
 APR_DECLARE_OPTIONAL_FN(int, ssl_is_https, (conn_rec *));
@@ -71,24 +72,16 @@ static char *mag_error(request_rec *req, const char *msg,
 
 static APR_OPTIONAL_FN_TYPE(ssl_is_https) *mag_is_https = NULL;
 
-static int mag_post_config(apr_pool_t *cfg, apr_pool_t *log,
+static int mag_post_config(apr_pool_t *cfgpool, apr_pool_t *log,
                            apr_pool_t *temp, server_rec *s)
 {
     /* FIXME: create mutex to deal with connections and contexts ? */
     mag_is_https = APR_RETRIEVE_OPTIONAL_FN(ssl_is_https);
+    mag_post_config_session();
 
     return OK;
 }
 
-
-struct mag_conn {
-    apr_pool_t *parent;
-    gss_ctx_id_t ctx;
-    bool established;
-    char *user_name;
-    char *gss_name;
-};
-
 static int mag_pre_connection(conn_rec *c, void *csd)
 {
     struct mag_conn *mc;
@@ -138,6 +131,7 @@ static int mag_auth(request_rec *req)
     gss_name_t client = GSS_C_NO_NAME;
     gss_cred_id_t delegated_cred = GSS_C_NO_CREDENTIAL;
     uint32_t flags;
+    uint32_t vtime;
     uint32_t maj, min;
     char *reply;
     size_t replen;
@@ -151,6 +145,11 @@ static int mag_auth(request_rec *req)
         return DECLINED;
     }
 
+    /* ignore auth for subrequests */
+    if (!ap_is_initial_req(req)) {
+        return OK;
+    }
+
     cfg = ap_get_module_config(req->per_dir_config, &auth_gssapi_module);
 
     if (cfg->ssl_only) {
@@ -166,11 +165,24 @@ static int mag_auth(request_rec *req)
                                                 req->connection->conn_config,
                                                 &auth_gssapi_module);
         if (!mc) {
-            return DECLINED;
+            ap_log_rerror(APLOG_MARK, APLOG_DEBUG|APLOG_NOERRNO, 0, req,
+                          "Failed to retrieve connection context!");
+            goto done;
         }
+    }
+
+    /* if available, session always supersedes connection bound data */
+    mag_check_session(req, cfg, &mc);
+
+    if (mc) {
+        /* register the context in the memory pool, so it can be freed
+         * when the connection/request is terminated */
+        apr_pool_userdata_set(mc, "mag_conn_ptr",
+                              mag_conn_destroy, mc->parent);
+
         if (mc->established) {
             ap_log_rerror(APLOG_MARK, APLOG_DEBUG|APLOG_NOERRNO, 0, req,
-                          "Connection bound pre-authentication found.");
+                          "Already established context found!");
             apr_table_set(req->subprocess_env, "GSS_NAME", mc->gss_name);
             req->ap_auth_type = apr_pstrdup(req->pool, "Negotiate");
             req->user = apr_pstrdup(req->pool, mc->user_name);
@@ -199,7 +211,7 @@ static int mag_auth(request_rec *req)
 
     maj = gss_accept_sec_context(&min, pctx, GSS_C_NO_CREDENTIAL,
                                  &input, GSS_C_NO_CHANNEL_BINDINGS,
-                                 &client, &mech_type, &output, &flags, NULL,
+                                 &client, &mech_type, &output, &flags, &vtime,
                                  &delegated_cred);
     if (GSS_ERROR(maj)) {
         ap_log_rerror(APLOG_MARK, APLOG_ERR|APLOG_NOERRNO, 0, req,
@@ -208,19 +220,17 @@ static int mag_auth(request_rec *req)
         goto done;
     }
 
-    /* register the context in the connection pool, so it can be freed
-     * when the connection is terminated */
-    apr_pool_userdata_set(mc, "mag_conn_ptr", mag_conn_destroy, mc->parent);
-
     if (maj == GSS_S_CONTINUE_NEEDED) {
-        if (!cfg->gss_conn_ctx) {
+        if (!mc) {
             ap_log_rerror(APLOG_MARK, APLOG_ERR|APLOG_NOERRNO, 0, req,
-                          "Mechanism needs continuation but "
-                          "GssapiConnectionBound is off.");
+                          "Mechanism needs continuation but neither "
+                          "GssapiConnectionBound nor "
+                          "GssapiUseSessions are available");
             gss_delete_sec_context(&min, pctx, GSS_C_NO_BUFFER);
             gss_release_buffer(&min, &output);
             output.length = 0;
         }
+        /* auth not complete send token and wait next packet */
         goto done;
     }
 
@@ -263,6 +273,11 @@ static int mag_auth(request_rec *req)
         mc->user_name = apr_pstrdup(mc->parent, req->user);
         mc->gss_name = apr_pstrdup(mc->parent, clientname);
         mc->established = true;
+        if (vtime == GSS_C_INDEFINITE || vtime < MIN_SESS_EXP_TIME) {
+            vtime = MIN_SESS_EXP_TIME;
+        }
+        mc->expiration = time(NULL) + vtime;
+        mag_attempt_session(req, cfg, mc);
     }
 
     ret = OK;
@@ -298,6 +313,7 @@ static void *mag_create_dir_config(apr_pool_t *p, char *dir)
 
     cfg = (struct mag_config *)apr_pcalloc(p, sizeof(struct mag_config));
     if (!cfg) return NULL;
+    cfg->pool = p;
 
     return cfg;
 }
@@ -323,6 +339,13 @@ static const char *mag_conn_ctx(cmd_parms *parms, void *mconfig, int on)
     return NULL;
 }
 
+static const char *mag_use_sess(cmd_parms *parms, void *mconfig, int on)
+{
+    struct mag_config *cfg = (struct mag_config *)mconfig;
+    cfg->use_sessions = on ? true : false;
+    return NULL;
+}
+
 static const char *mag_cred_store(cmd_parms *parms, void *mconfig,
                                   const char *w)
 {
@@ -376,6 +399,8 @@ static const command_rec mag_commands[] = {
                   "Work only if connection is SSL Secured"),
     AP_INIT_FLAG("GssapiConnectionBound", mag_conn_ctx, NULL, OR_AUTHCFG,
                   "Authentication is bound to the TCP connection"),
+    AP_INIT_FLAG("GssapiUseSessions", mag_use_sess, NULL, OR_AUTHCFG,
+                  "Authentication uses mod_sessions to hold status"),
     AP_INIT_ITERATE("GssapiCredStore", mag_cred_store, NULL, OR_AUTHCFG,
                     "Credential Store"),
     { NULL }