agent: New option --auto-expand-secmem.

* agent/gpg-agent.c (oAutoExpandSecmem): New enum value.
(opts): New option --auto-expand-secmem.
(main): Implement that option.
--

Note that this option has an effect only if Libgcrypt >= 1.8.2 is
used.

GnuPG-bug-id: 3530

agent/gpg-agent.c

@@ -135,6 +135,7 @@ enum cmd_and_opt_values
   oDisableScdaemon,
   oDisableCheckOwnSocket,
   oS2KCount,
+  oAutoExpandSecmem,
 
   oWriteEnvFile
 };
@@ -252,6 +253,8 @@ static ARGPARSE_OPTS opts[] = {
 
   ARGPARSE_s_u (oS2KCount, "s2k-count", "@"),
 
+  ARGPARSE_op_u (oAutoExpandSecmem, "auto-expand-secmem", "@"),
+
   /* Dummy options for backward compatibility.  */
   ARGPARSE_o_s (oWriteEnvFile, "write-env-file", "@"),
   ARGPARSE_s_n (oUseStandardSocket, "use-standard-socket", "@"),
@@ -1233,6 +1236,14 @@ main (int argc, char **argv )
           socket_name_browser = pargs.r.ret_str;
           break;
 
+        case oAutoExpandSecmem:
+          /* Try to enable this option.  It will officially only be
+           * supported by Libgcrypt 1.9 but 1.8.2 already supports it
+           * on the quiet and thus we use the numeric value value.  */
+          gcry_control (78 /*GCRYCTL_AUTO_EXPAND_SECMEM*/,
+                        (unsigned int)pargs.r.ret_ulong,  0);
+          break;
+
         case oDebugQuickRandom:
           /* Only used by the first stage command line parser.  */
           break;

doc/gpg-agent.texi

@@ -652,6 +652,17 @@ Select the digest algorithm used to compute ssh fingerprints that are
 communicated to the user, e.g. in pinentry dialogs.  OpenSSH has
 transitioned from using MD5 to the more secure SHA256.
 
+
+@item --auto-expand-secmem @var{n}
+@opindex auto-expand-secmem
+gAllow Libgcrypt to expand its secure memory area as required.  The
+optional value @var{n} is a non-negative integer with a suggested size
+in bytes of each additionally allocated secure memory area.  The value
+is rounded up to the next 32 KiB; usual C style prefixes are allowed.
+For an heavy loaded gpg-agent with many concurrent connection this
+option avoids sign or decrypt errors due to out of secure memory error
+returns.
+
 @item --s2k-count @var{n}
 @opindex s2k-count
 Specify the iteration count used to protect the passphrase.  This