Special ccache handling for {HOSTNAME} acceptor

This applies only to the case when GssapiS4U2Proxy is enabled.

When using the {HOSTNAME} acceptor, the principal used in the server
ccache can vary with each request. GSSAPI does not handle gracefully
a request to resolve a ccache if there is already another credential
under a different name. Even with ccache collections GSSAPI will
resolve an existing ccache from the collection if any is available and
throw an error if it does not match the desired_name. This even if
there is a client_keytab that could be used to initiate a new cache in
the collection with the right name.

Therefore in case GssapiAcceptor is set to the special value {HOSTNAME},
instead of using the provided ccache or the process default ccache we
create a new ccache named after the hostname in the delegated ccache
directory. This directory is required when the S4U2Proxy mode is enabled
so we are guaranteed to have it available an writable.

Signed-off-by: Simo Sorce <simo@redhat.com>
[rharwood@redhat.com: nits]

Author: simo5

src/mod_auth_gssapi.c

@@ -194,6 +194,9 @@ static bool mag_conn_is_https(conn_rec *c)
     return false;
 }
 
+static char *get_ccache_name(request_rec *req, char *dir, const char *name,
+                             bool use_unique, apr_pool_t *pool);
+
 static bool mag_acquire_creds(request_rec *req,
                               struct mag_config *cfg,
                               gss_OID_set desired_mechs,
@@ -226,7 +229,52 @@ static bool mag_acquire_creds(request_rec *req,
     }
 
 #ifdef HAVE_CRED_STORE
-    gss_const_key_value_set_t store = cfg->cred_store;
+    gss_const_key_value_set_t store = NULL;
+
+    /* When using multiple names, we need to use individual separate ccaches
+     * for each principal or gss_acquire_cred() on the default ccache will
+     * fail when names don't match.  This is needed only for the s4u2proxy
+     * case, where we try to acquire proxy credentials.  The lucky thing is
+     * that in this case we require the use of a delegated creedntials
+     * directory, so we just use this directory to also hold permanent ccaches
+     * for individual acceptor names. */
+    if (cfg->acceptor_name_from_req && cfg->use_s4u2proxy &&
+        cfg->deleg_ccache_dir) {
+
+        gss_key_value_set_desc *s;
+        bool add = true;
+        char *ccname;
+        char *special_name;
+
+        special_name = apr_psprintf(req->pool, "acceptor_%s", req->hostname);
+        ccname = get_ccache_name(req, cfg->deleg_ccache_dir, special_name,
+                                 false, req->pool);
+
+        s = apr_pcalloc(req->pool, sizeof(gss_key_value_set_desc));
+        s->count = cfg->cred_store->count;
+        s->elements = apr_pcalloc(req->pool,
+                                  (s->count + 1) *
+                                  sizeof(gss_key_value_element_desc));
+        for (size_t i = 0; i < s->count; i++) {
+            gss_key_value_element_desc *el = &cfg->cred_store->elements[i];
+            s->elements[i].key = el->key;
+            if (strcmp(el->key, "ccache") == 0) {
+                s->elements[i].value = ccname;
+                add = false;
+            } else {
+                s->elements[i].value = el->value;
+            }
+        }
+        if (add) {
+            s->elements[s->count].key = "ccache";
+            s->elements[s->count].value = ccname;
+            s->count++;
+        }
+
+        store = s;
+    } else {
+        store = cfg->cred_store;
+    }
 
     maj = gss_acquire_cred_from(&min, acceptor_name, GSS_C_INDEFINITE,
                                 desired_mechs, cred_usage, store, creds,
@@ -287,8 +335,8 @@ static char *escape(apr_pool_t *pool, const char *name,
     return escaped;
 }
 
-static char *get_ccache_name(request_rec *req, char *dir, const char *gss_name,
-                             bool use_unique, struct mag_conn *mc)
+static char *get_ccache_name(request_rec *req, char *dir, const char *name,
+                             bool use_unique, apr_pool_t *pool)
 {
     char *ccname, *escaped;
     int ccachefd;
@@ -297,15 +345,15 @@ static char *get_ccache_name(request_rec *req, char *dir, const char *gss_name,
     /* We need to escape away '/', we can't have path separators in
      * a ccache file name */
     /* first double escape the esacping char (~) if any */
-    escaped = escape(req->pool, gss_name, '~', "~~");
+    escaped = escape(req->pool, name, '~', "~~");
     /* then escape away the separator (/) if any */
     escaped = escape(req->pool, escaped, '/', "~");
 
     if (use_unique == false) {
-        return apr_psprintf(mc->pool, "%s/%s", dir, escaped);
+        return apr_psprintf(pool, "%s/%s", dir, escaped);
     }
 
-    ccname = apr_psprintf(mc->pool, "%s/%s-XXXXXX", dir, escaped);
+    ccname = apr_psprintf(pool, "%s/%s-XXXXXX", dir, escaped);
 
     umask_save = umask(0177);
     ccachefd = mkstemp(ccname);
@@ -1297,7 +1345,7 @@ static int mag_complete(struct mag_req_cfg *req_cfg, struct mag_conn *mc,
                       "requester: %s", mc->gss_name);
 
         ccache_path = get_ccache_name(req, cfg->deleg_ccache_dir, mc->gss_name,
-                                      cfg->deleg_ccache_unique, mc);
+                                      cfg->deleg_ccache_unique, mc->pool);
         if (ccache_path == NULL) {
             goto done;
         }