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]>

1 files changed, 5 insertions, 2 deletions

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;