secure the tty

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

1 files changed, 82 insertions, 0 deletions

diff --git a/src/security.c b/src/security.c
new file mode 100644
index 0000000..04ec33d
--- /dev/null
+++ b/src/security.c
@@ -0,0 +1,82 @@
+/**
+ * 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 "security.h"
+
+
+#ifndef TTY_PERM
+#define TTY_PERM  0600
+#endif
+
+#ifndef FAILURE_SLEEP
+#define FAILURE_SLEEP  5
+#endif
+
+
+#define fail(FUNC)  ({ perror(#FUNC); sleep(FAILURE_SLEEP); _exit(1); })
+
+
+
+/**
+ * Secure the TTY from spying
+ */
+void secure_tty(void) /* TODO /dev/vcs[a][0-9]+ */
+{
+  struct termios tty;
+  struct termios saved_tty;
+  char* tty_device;
+  int fd, i;
+  
+  /* Take owner ship of this TTY */
+  if (fchown(STDIN_FILENO, 0, 0))
+    fail(fchown);
+  
+  /* Restrict others from using this TTY */
+  if (fchmod(STDIN_FILENO, TTY_PERM))
+    fail(fchmod);
+  
+  /* Get TTY name for last part of this functions */
+  tty_device = ttyname(STDIN_FILENO);
+  
+  /* Kill other processes on this TTY */
+  tcgetattr(STDIN_FILENO, &tty);
+  saved_tty = tty;
+  tty.c_cflag &= ~HUPCL;
+  tcsetattr(0, TCSANOW, &tty);
+  close(STDIN_FILENO);
+  close(STDOUT_FILENO);
+  close(STDERR_FILENO);
+  signal(SIGHUP, SIG_IGN);
+  vhangup();
+  signal(SIGHUP, SIG_DFL);
+  
+  /* Restore terminal and TTY modes */
+  fd = open(tty_device, O_RDWR | O_NONBLOCK);
+  if (fd == -1)
+    fail(open);
+  fcntl(fd, F_SETFL, fcntl(fd, F_GETFL) & ~O_NONBLOCK);
+  for (i = 0; i < fd; i++)
+    close(i);
+  for (i = 0; i < 3; i++)
+    if (i != fd)
+      dup2(fd, i);
+  if (fd > 2)
+    close(fd);
+  tcgetattr(STDIN_FILENO, &saved_tty);
+}
+