read passphrase

Signed-off-by: Mattias Andrée <maandree@operamail.com>

1 files changed, 89 insertions, 0 deletions

diff --git a/src/passphrase.c b/src/passphrase.c
new file mode 100644
index 0000000..cd88c7f
--- /dev/null
+++ b/src/passphrase.c
@@ -0,0 +1,89 @@
+/**
+ * cerberus – Minimal login program
+ * 
+ * Copyright © 2013  Mattias Andrée (maandree@member.fsf.org)
+ * 
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ * 
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ * 
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+#include "passphrase.h"
+
+
+#define START_PASSPHRASE_LIMIT  32
+
+
+/**
+ * The original TTY settings
+ */
+static struct termios saved_stty;
+
+
+/**
+ * Reads the passphrase from stdin
+ * 
+ * @return  The passphrase, should be `free`:ed
+ */
+char* get_passphrase(void)
+{
+  /* malloc and realloc returns NULL if we run out of memory,
+     we will not do that under normal usecases, if we do, it
+     okay to segfault on null derefencing and quit on that. */
+  
+  char* rc = malloc(START_PASSPHRASE_LIMIT);
+  long size = START_PASSPHRASE_LIMIT;
+  long len = 0;
+  int c;
+  
+  /* Read password until EOF or Enter, skip all ^0 as that
+     is probably not a part of the passphrase (good luck typing
+     that in X.org) and can be echoed into stdin by the kernel. */
+  for (;;)
+    {
+      c = getchar();
+      if ((c < 0) || (c == '\n'))
+	break;
+      if (c != 0)
+        {
+	  *(rc + len++) = c;
+	  if (len == size)
+	    rc = realloc(rc, size <<= 1L);
+	}
+    }
+  
+  /* NUL-terminate passphrase */
+  *(rc + len) = 0;
+  
+  return rc;
+}
+
+
+/**
+ * Disable echoing and do anything else to the terminal settnings `get_passphrase` requires
+ */
+void disable_echo()
+{
+  tcgetattr(STDIN_FILENO, &saved_stty);
+  stty = saved_stty;
+  stty.c_lflag &= ~ECHO;
+  tcsetattr(STDIN_FILENO, TCSAFLUSH, &stty);
+}
+
+
+/**
+ * Undo the actions of `disable_echo`
+ */
+void reenable_echo()
+{
+  tcsetattr(STDIN_FILENO, TCSAFLUSH, &saved_stty);
+}
+