gpg-agent: add new CACHE_MODE_EXPORTdkg/fix-T4522

* agent/agent.h: define CACHE_MODE_EXPORT
* agent/call-pinentry.c (agent_askpin, agent_get_passphrase): use "e/"
as the prefix for SETKEYINFO when in CACHE_MODE_EXPORT.
(agent_clear_passphrase): allow clearing the export cache.
* agent/command.c (cmd_clear_passphrase): add --mode=export.
(cmd_export_key): use CACHE_MODE_EXPORT.
* tests/openpgp/export.scm: no need to feed passphrases during export,
already cached.

----

We don't want secret keys to be able to be exported automatically
based on the same system passphrase cache used by standard decryption
or signing operations.

So we introduce a "export" cache mode which can be used by EXPORT_KEY.

I confess i don't fully understand the changes made to
tests/openpgp/export.scm -- i'm not sure why the passphrase is already
supplied in this case.

Gnupg-Bug-Id: 4522
Signed-off-by: Daniel Kahn Gillmor <[email protected]>

3 files changed, 17 insertions, 8 deletions

diff --git a/agent/agent.h b/agent/agent.h
index 77672bd50..8c4a1d4ba 100644
--- a/agent/agent.h
+++ b/agent/agent.h
@@ -322,7 +322,8 @@ typedef enum
     CACHE_MODE_USER,       /* GET_PASSPHRASE related cache. */
     CACHE_MODE_SSH,        /* SSH related cache. */
     CACHE_MODE_NONCE,      /* This is a non-predictable nonce.  */
-    CACHE_MODE_DATA        /* Arbitrary data.  */
+    CACHE_MODE_DATA,       /* Arbitrary data.  */
+    CACHE_MODE_EXPORT,     /* Exporting secret keys.  */
   }
 cache_mode_t;
 
diff --git a/agent/call-pinentry.c b/agent/call-pinentry.c
index 5b4713f41..bf75bb4a7 100644
--- a/agent/call-pinentry.c
+++ b/agent/call-pinentry.c
@@ -1120,10 +1120,12 @@ agent_askpin (ctrl_t ctrl,
      we do not error out in this case.  */
   if (keyinfo && (cache_mode == CACHE_MODE_NORMAL
                   || cache_mode == CACHE_MODE_USER
-                  || cache_mode == CACHE_MODE_SSH))
+                  || cache_mode == CACHE_MODE_SSH
+                  || cache_mode == CACHE_MODE_EXPORT))
     snprintf (line, DIM(line), "SETKEYINFO %c/%s",
 	      cache_mode == CACHE_MODE_USER? 'u' :
-	      cache_mode == CACHE_MODE_SSH? 's' : 'n',
+	      cache_mode == CACHE_MODE_SSH? 's' :
+	      cache_mode == CACHE_MODE_EXPORT? 'e' : 'n',
 	      keyinfo);
   else
     snprintf (line, DIM(line), "SETKEYINFO --clear");
@@ -1313,10 +1315,12 @@ agent_get_passphrase (ctrl_t ctrl,
      we do not error out in this case.  */
   if (keyinfo && (cache_mode == CACHE_MODE_NORMAL
                   || cache_mode == CACHE_MODE_USER
-                  || cache_mode == CACHE_MODE_SSH))
+                  || cache_mode == CACHE_MODE_SSH
+                  || cache_mode == CACHE_MODE_EXPORT))
     snprintf (line, DIM(line), "SETKEYINFO %c/%s",
 	      cache_mode == CACHE_MODE_USER? 'u' :
-	      cache_mode == CACHE_MODE_SSH? 's' : 'n',
+	      cache_mode == CACHE_MODE_SSH? 's' :
+              cache_mode == CACHE_MODE_EXPORT? 'e' : 'n',
 	      keyinfo);
   else
     snprintf (line, DIM(line), "SETKEYINFO --clear");
@@ -1635,7 +1639,8 @@ agent_clear_passphrase (ctrl_t ctrl,
 
   if (! (keyinfo && (cache_mode == CACHE_MODE_NORMAL
 		     || cache_mode == CACHE_MODE_USER
-		     || cache_mode == CACHE_MODE_SSH)))
+		     || cache_mode == CACHE_MODE_SSH
+		     || cache_mode == CACHE_MODE_EXPORT)))
     return gpg_error (GPG_ERR_NOT_SUPPORTED);
 
   rc = start_pinentry (ctrl);
diff --git a/agent/command.c b/agent/command.c
index c056eb3f0..a86c9fff5 100644
--- a/agent/command.c
+++ b/agent/command.c
@@ -1611,7 +1611,8 @@ static const char hlp_clear_passphrase[] =
   "function returns with OK even when there is no cached passphrase.\n"
   "The --mode=normal option is used to clear an entry for a cacheid\n"
   "added by the agent.  The --mode=ssh option is used for a cacheid\n"
-  "added for ssh.\n";
+  "added for ssh.  The --mode=export option is used for a cacheid\n"
+  "added for secret key export.\n";
 static gpg_error_t
 cmd_clear_passphrase (assuan_context_t ctx, char *line)
 {
@@ -1627,6 +1628,8 @@ cmd_clear_passphrase (assuan_context_t ctx, char *line)
     cache_mode = CACHE_MODE_NORMAL;
   else if (has_option (line, "--mode=ssh"))
     cache_mode = CACHE_MODE_SSH;
+  else if (has_option (line, "--mode=export"))
+    cache_mode = CACHE_MODE_EXPORT;
 
   line = skip_options (line);
 
@@ -2347,7 +2350,7 @@ cmd_export_key (assuan_context_t ctx, char *line)
      the passphrase so that we can use it to re-encrypt it.  */
   err = agent_key_from_file (ctrl, cache_nonce,
                              ctrl->server_local->keydesc, grip,
-                             &shadow_info, CACHE_MODE_IGNORE, NULL, &s_skey,
+                             &shadow_info, CACHE_MODE_EXPORT, NULL, &s_skey,
                              openpgp ? &passphrase : NULL);
   if (err)
     goto leave;