sm: Lookup missing issuers first using authorityInfoAccess.

* sm/call-dirmngr.c (gpgsm_dirmngr_lookup): Add optional arg URL and
adjust all callers.
* sm/certchain.c (oidstr_caIssuers): New.
(struct find_up_store_certs_s): Add additional fields.
(find_up_store_certs_cb): Store the fingerprint.
(find_up_via_auth_info_access): New.
(find_up): Try the AIA URI first.
--

Note that --auto-issuer-key-retrieve is required to use that.

GnuPG-bug-id: 4898
Signed-off-by: Werner Koch <wk@gnupg.org>

sm/call-dirmngr.c

@@ -757,20 +757,24 @@ lookup_status_cb (void *opaque, const char *line)
 
 
 /* Run the Directory Manager's lookup command using the pattern
-   compiled from the strings given in NAMES.  The caller must provide
-   the callback CB which will be passed cert by cert.  Note that CTRL
-   is optional.  With CACHE_ONLY the dirmngr will search only its own
-   key cache. */
+   compiled from the strings given in NAMES or from URI.  The caller
+   must provide the callback CB which will be passed cert by cert.
+   Note that CTRL is optional.  With CACHE_ONLY the dirmngr will
+   search only its own key cache. */
 int
-gpgsm_dirmngr_lookup (ctrl_t ctrl, strlist_t names, int cache_only,
+gpgsm_dirmngr_lookup (ctrl_t ctrl, strlist_t names, const char *uri,
+                      int cache_only,
                       void (*cb)(void*, ksba_cert_t), void *cb_value)
 {
   int rc;
-  char *pattern;
   char line[ASSUAN_LINELENGTH];
   struct lookup_parm_s parm;
   size_t len;
   assuan_context_t ctx;
+  const char *s;
+
+  if ((names && uri) || (!names && !uri))
+    return gpg_error (GPG_ERR_INV_ARG);
 
   /* The lookup function can be invoked from the callback of a lookup
      function, for example to walk the chain.  */
@@ -793,19 +797,35 @@ gpgsm_dirmngr_lookup (ctrl_t ctrl, strlist_t names, int cache_only,
       log_fatal ("both dirmngr contexts are in use\n");
     }
 
-  pattern = pattern_from_strlist (names);
-  if (!pattern)
+  if (names)
     {
-      if (ctx == dirmngr_ctx)
-	release_dirmngr (ctrl);
-      else
-	release_dirmngr2 (ctrl);
+      char *pattern = pattern_from_strlist (names);
+      if (!pattern)
+        {
+          if (ctx == dirmngr_ctx)
+            release_dirmngr (ctrl);
+          else
+            release_dirmngr2 (ctrl);
 
-      return out_of_core ();
+          return out_of_core ();
+        }
+      snprintf (line, DIM(line), "LOOKUP%s %s",
+                cache_only? " --cache-only":"", pattern);
+      xfree (pattern);
+    }
+  else
+    {
+      for (s=uri; *s; s++)
+        if (*s <= ' ')
+          {
+            if (ctx == dirmngr_ctx)
+              release_dirmngr (ctrl);
+            else
+              release_dirmngr2 (ctrl);
+            return gpg_error (GPG_ERR_INV_URI);
+          }
+      snprintf (line, DIM(line), "LOOKUP --url %s", uri);
     }
-  snprintf (line, DIM(line), "LOOKUP%s %s",
-            cache_only? " --cache-only":"", pattern);
-  xfree (pattern);
 
   parm.ctrl = ctrl;
   parm.ctx = ctx;

sm/certchain.c

@@ -38,6 +38,10 @@
 #include "../common/tlv.h"
 
 
+/* The OID for the authorityInfoAccess's caIssuers.  */
+static const char oidstr_caIssuers[] = "1.3.6.1.5.5.7.48.2";
+
+
 /* Object to keep track of certain root certificates. */
 struct marktrusted_info_s
 {
@@ -574,6 +578,9 @@ struct find_up_store_certs_s
 {
   ctrl_t ctrl;
   int count;
+  unsigned int want_fpr:1;
+  unsigned int got_fpr:1;
+  unsigned char fpr[20];
 };
 
 static void
@@ -583,6 +590,13 @@ find_up_store_certs_cb (void *cb_value, ksba_cert_t cert)
 
   if (keydb_store_cert (parm->ctrl, cert, 1, NULL))
     log_error ("error storing issuer certificate as ephemeral\n");
+  else if (parm->want_fpr && !parm->got_fpr)
+    {
+      if (!gpgsm_get_fingerprint (cert, 0, parm->fpr, NULL))
+        log_error (_("failed to get the fingerprint\n"));
+      else
+        parm->got_fpr = 1;
+    }
   parm->count++;
 }
 
@@ -603,6 +617,8 @@ find_up_external (ctrl_t ctrl, KEYDB_HANDLE kh,
   const char *s;
 
   find_up_store_certs_parm.ctrl = ctrl;
+  find_up_store_certs_parm.want_fpr = 0;
+  find_up_store_certs_parm.got_fpr = 0;
   find_up_store_certs_parm.count = 0;
 
   if (opt.verbose)
@@ -621,7 +637,7 @@ find_up_external (ctrl_t ctrl, KEYDB_HANDLE kh,
   add_to_strlist (&names, pattern);
   xfree (pattern);
 
-  rc = gpgsm_dirmngr_lookup (ctrl, names, 0, find_up_store_certs_cb,
+  rc = gpgsm_dirmngr_lookup (ctrl, names, NULL, 0, find_up_store_certs_cb,
                              &find_up_store_certs_parm);
   free_strlist (names);
 
@@ -654,6 +670,105 @@ find_up_external (ctrl_t ctrl, KEYDB_HANDLE kh,
 }
 
 
+/* Helper for find_up().  Locate the certificate for CERT using the
+ * caIssuer from the authorityInfoAccess.  KH is the keydb context we
+ * are currently using.  On success 0 is returned and the certificate
+ * may be retrieved from the keydb using keydb_get_cert().  If no
+ * suitable authorityInfoAccess is encoded in the certificate
+ * GPG_ERR_NOT_FOUND is returned. */
+static gpg_error_t
+find_up_via_auth_info_access (ctrl_t ctrl, KEYDB_HANDLE kh, ksba_cert_t cert)
+{
+  gpg_error_t err;
+  struct find_up_store_certs_s find_up_store_certs_parm;
+  char *url, *ldapurl;
+  int idx, i;
+  char *oid;
+  ksba_name_t name;
+
+  find_up_store_certs_parm.ctrl = ctrl;
+  find_up_store_certs_parm.want_fpr = 1;
+  find_up_store_certs_parm.got_fpr = 0;
+  find_up_store_certs_parm.count = 0;
+
+  /* Find suitable URLs; if there is a http scheme we prefer that.  */
+  url = ldapurl = NULL;
+  for (idx=0;
+       !url && !(err = ksba_cert_get_authority_info_access (cert, idx,
+                                                            &oid, &name));
+       idx++)
+    {
+      if (!strcmp (oid, oidstr_caIssuers))
+        {
+          for (i=0; !url && ksba_name_enum (name, i); i++)
+            {
+              char *p = ksba_name_get_uri (name, i);
+              if (p)
+                {
+                  if (!strncmp (p, "http:", 5) || !strncmp (p, "https:", 6))
+                    url = p;
+                  else if (ldapurl)
+                    xfree (p); /* We already got one.  */
+                  else if (!strncmp (p, "ldap:",5) || !strncmp (p, "ldaps:",6))
+                    ldapurl = p;
+                }
+              else
+                xfree (p);
+            }
+        }
+      ksba_name_release (name);
+      ksba_free (oid);
+    }
+  if (err && gpg_err_code (err) != GPG_ERR_EOF)
+    {
+      log_error (_("can't get authorityInfoAccess: %s\n"), gpg_strerror (err));
+      return err;
+    }
+  if (!url && ldapurl)
+    {
+      /* No HTTP scheme; fallback to LDAP if available.  */
+      url = ldapurl;
+      ldapurl = NULL;
+    }
+  xfree (ldapurl);
+  if (!url)
+    return gpg_error (GPG_ERR_NOT_FOUND);
+
+  if (opt.verbose)
+    log_info ("looking up issuer via authorityInfoAccess.caIssuers\n");
+
+  err = gpgsm_dirmngr_lookup (ctrl, NULL, url, 0, find_up_store_certs_cb,
+                              &find_up_store_certs_parm);
+
+  /* Although we might receive several certificates we use only the
+   * first one.  Or more exacty the first one for which we retrieved
+   * the fingerprint.  */
+  if (opt.verbose)
+    log_info ("number of caIssuers found: %d\n",
+              find_up_store_certs_parm.count);
+  if (err)
+    {
+      log_error ("external URL lookup failed: %s\n", gpg_strerror (err));
+      err = gpg_error (GPG_ERR_NOT_FOUND);
+    }
+  else if (!find_up_store_certs_parm.got_fpr)
+    err = gpg_error (GPG_ERR_NOT_FOUND);
+  else
+    {
+      int old;
+      /* The retrieved certificates are currently stored in the
+       * ephemeral key DB, so we temporary switch to ephemeral
+       * mode. */
+      old = keydb_set_ephemeral (kh, 1);
+      keydb_search_reset (kh);
+      err = keydb_search_fpr (ctrl, kh, find_up_store_certs_parm.fpr);
+      keydb_set_ephemeral (kh, old);
+    }
+
+  return err;
+}
+
+
 /* Helper for find_up().  Ask the dirmngr for the certificate for
    ISSUER with optional SERIALNO.  KH is the keydb context we are
    currently using.  With SUBJECT_MODE set, ISSUER is searched as the
@@ -694,7 +809,7 @@ find_up_dirmngr (ctrl_t ctrl, KEYDB_HANDLE kh,
   add_to_strlist (&names, pattern);
   xfree (pattern);
 
-  rc = gpgsm_dirmngr_lookup (ctrl, names, 1, find_up_store_certs_cb,
+  rc = gpgsm_dirmngr_lookup (ctrl, names, NULL, 1, find_up_store_certs_cb,
                              &find_up_store_certs_parm);
   free_strlist (names);
 
@@ -816,9 +931,18 @@ find_up (ctrl_t ctrl, KEYDB_HANDLE kh,
       /* If we still didn't found it, try an external lookup.  */
       if (rc == -1 && opt.auto_issuer_key_retrieve && !find_next)
         {
-          rc = find_up_external (ctrl, kh, issuer, keyid);
-          if (!rc && DBG_X509)
-            log_debug ("  found via authid and external lookup\n");
+          if (!find_up_via_auth_info_access (ctrl, kh, cert))
+            {
+              if (DBG_X509)
+                log_debug ("  found via authorityInfoAccess.caIssuers\n");
+              rc = 0;
+            }
+          else
+            {
+              rc = find_up_external (ctrl, kh, issuer, keyid);
+              if (!rc && DBG_X509)
+                log_debug ("  found via authid and external lookup\n");
+            }
         }
 
 
@@ -879,9 +1003,18 @@ find_up (ctrl_t ctrl, KEYDB_HANDLE kh,
   /* Still not found.  If enabled, try an external lookup.  */
   if (rc == -1 && opt.auto_issuer_key_retrieve && !find_next)
     {
-      rc = find_up_external (ctrl, kh, issuer, NULL);
-      if (!rc && DBG_X509)
-        log_debug ("  found via issuer and external lookup\n");
+      if (!find_up_via_auth_info_access (ctrl, kh, cert))
+        {
+          if (DBG_X509)
+            log_debug ("  found via authorityInfoAccess.caIssuers\n");
+          rc = 0;
+        }
+      else
+        {
+          rc = find_up_external (ctrl, kh, issuer, NULL);
+          if (!rc && DBG_X509)
+            log_debug ("  found via issuer and external lookup\n");
+        }
     }
 
   return rc;

sm/gpgsm.h

@@ -447,7 +447,8 @@ gpg_error_t gpgsm_agent_export_key (ctrl_t ctrl, const char *keygrip,
 int gpgsm_dirmngr_isvalid (ctrl_t ctrl,
                            ksba_cert_t cert, ksba_cert_t issuer_cert,
                            int use_ocsp);
-int gpgsm_dirmngr_lookup (ctrl_t ctrl, strlist_t names, int cache_only,
+int gpgsm_dirmngr_lookup (ctrl_t ctrl, strlist_t names, const char *uri,
+                          int cache_only,
                           void (*cb)(void*, ksba_cert_t), void *cb_value);
 int gpgsm_dirmngr_run_command (ctrl_t ctrl, const char *command,
                                int argc, char **argv);

sm/keylist.c

@@ -1648,7 +1648,7 @@ list_external_keys (ctrl_t ctrl, strlist_t names, estream_t fp, int raw_mode)
   parm.with_chain = ctrl->with_chain;
   parm.raw_mode  = raw_mode;
 
-  rc = gpgsm_dirmngr_lookup (ctrl, names, 0, list_external_cb, &parm);
+  rc = gpgsm_dirmngr_lookup (ctrl, names, NULL, 0, list_external_cb, &parm);
   if (gpg_err_code (rc) == GPG_ERR_EOF || rc == -1
       || gpg_err_code (rc) == GPG_ERR_NOT_FOUND)
     rc = 0; /* "Not found" is not an error here. */