gpg: Make sure that we are not accidently working with the PIV app.

* g10/call-agent.c (agent_scd_switchapp): New.
* g10/card-util.c (get_info_for_key_operation): Call it.
--

It may happen that the active card was last used for PIV and in that
case certain commands will fail because they assume the OpenPGP app.
Fortunately we have a pretty central place to assure that the right
app has been selected.

The bug can be easily noticed on Windows.

GnuPG-bug-id: 6378

NEWS

@@ -31,6 +31,8 @@ Noteworthy changes in version 2.4.1 (unreleased)
   * gpg: Make list-options "show-sig-subpackets" work again.
     Fixes regression in 2.4.0.  [rG5a223303d7]
 
+  * gpg: Fix the keytocard command for Yubikeys.  [T6378]
+
 
   Release-info: https://dev.gnupg.org/T6454
 

g10/call-agent.c

@@ -1700,6 +1700,30 @@ agent_scd_cardlist (strlist_t *result)
 }
 
 
+/* Make the app APPNAME the one on the card.  This is sometimes
+ * required to make sure no other process has switched a card to
+ * another application.  The only useful APPNAME is "openpgp".  */
+gpg_error_t
+agent_scd_switchapp (const char *appname)
+{
+  int err;
+  char line[ASSUAN_LINELENGTH];
+
+  if (appname && !*appname)
+    appname = NULL;
+
+  err = start_agent (NULL, (1 | FLAG_FOR_CARD_SUPPRESS_ERRORS));
+  if (err)
+    return err;
+
+  snprintf (line, DIM(line), "SCD SWITCHAPP --%s%s",
+            appname? " ":"", appname? appname:"");
+  return assuan_transact (agent_ctx, line,
+                          NULL, NULL, NULL, NULL,
+                          NULL, NULL);
+}
+
+
 
 struct card_keyinfo_parm_s {
   int error;

g10/call-agent.h

@@ -108,6 +108,9 @@ gpg_error_t agent_scd_keypairinfo (ctrl_t ctrl, const char *keyref,
 /* Return list of cards.  */
 int agent_scd_cardlist (strlist_t *result);
 
+/* Switch/assure a certain application. */
+gpg_error_t agent_scd_switchapp (const char *appname);
+
 /* Free a keypair info list.  */
 void free_keypair_info (keypair_info_t l);
 

g10/card-util.c

@@ -1289,6 +1289,7 @@ get_info_for_key_operation (struct agent_card_info_s *info)
   int rc;
 
   memset (info, 0, sizeof *info);
+  agent_scd_switchapp ("openpgp");
   rc = agent_scd_getattr ("SERIALNO", info);
   if (rc || !info->serialno || strncmp (info->serialno, "D27600012401", 12)
       || strlen (info->serialno) != 32 )