svn commit: r294691 - head/lib/libc/gen

[Maxim Sobolev]

Author: sobomax
Date: Sun Jan 24 22:20:13 2016
New Revision: 294691
URL: https://svnweb.freebsd.org/changeset/base/294691

Log:
  Fix bug in the readpassphrase(3) function, which can be exposed
  by application closing its stdin (i.e. STDIN_FILENO) prior to
  calling readpassphrase WITHOUT setting RPP_STDIN. What happens
  then is that the readpassphrase would open /dev/tty, and since
  file descriptors are reused, the call would return first unused
  fd, which is 0 which is also STDIN_FILENO. Then due to the usage
  of "input != STDIN_FILENO" in the code to do its logic, that
  would result in noecho flags not set on that file descriptor,
  which was original issue I've been trying to fix.
  
  In addition to that, the readpassphrase() would leak file
  descriptor on its way out, so fix that one as well.
  
  This problem can be tested with:
  
   $ ssh-add - < /tmp/myprivate.key
  
  The password will not be hidden as it should and ktrace will
  show:
  
   53326 ssh-add  CALL  open(0x80142443c,0x100002<O_RDWR|O_CLOEXEC>,<unused>0x165f030)
   53326 ssh-add  NAMI  "/dev/tty"
   53326 ssh-add  RET   open 0
   53326 ssh-add  CALL  sigprocmask(SIG_SETMASK,0x802eb1324,0x7fffffffd5e0)
   53326 ssh-add  RET   sigprocmask 0
   53326 ssh-add  CALL  sigaction(SIGALRM,0x7fffffffd630,0x7fffffffd610)
  
  Instead of:
  
   57690 ssh-add  CALL  open(0x80142443c,0x100002<O_RDWR|O_CLOEXEC>,<unused>0x165f030)
   57690 ssh-add  NAMI  "/dev/tty"
   57690 ssh-add  RET   open 4
   57690 ssh-add  CALL  ioctl(0x4,TIOCGETA,0x7fffffffd860)
   57690 ssh-add  RET   ioctl 0
   57690 ssh-add  CALL  ioctl(0x4,TIOCSETAF,0x7fffffffd680)
   57690 ssh-add  RET   ioctl 0
   57690 ssh-add  CALL  sigprocmask(SIG_SETMASK,0x802eb1324,0x7fffffffd620)
   57690 ssh-add  RET   sigprocmask 0
   57690 ssh-add  CALL  sigaction(SIGALRM,0x7fffffffd670,0x7fffffffd650)
  
  For the case when the key is read from the file.
  
  Technically this can also be workaround'ed at the application side
  by not closing the STDIN_FILENO in the first place, but readpassphrase(3)
  doesn't need to make any assumptions about that. Plus the file descriptor
  leak confirms that this is an oversight, rather than a deliberate behaviour.
  
  MFC after:	1 week

Modified:
  head/lib/libc/gen/readpassphrase.c

Modified: head/lib/libc/gen/readpassphrase.c
==============================================================================
--- head/lib/libc/gen/readpassphrase.c	Sun Jan 24 22:17:05 2016	(r294690)
+++ head/lib/libc/gen/readpassphrase.c	Sun Jan 24 22:20:13 2016	(r294691)
@@ -46,7 +46,7 @@ char *
 readpassphrase(const char *prompt, char *buf, size_t bufsiz, int flags)
 {
 	ssize_t nr;
-	int input, output, save_errno, i, need_restart;
+	int input, output, save_errno, i, need_restart, input_is_tty;
 	char ch, *p, *end;
 	struct termios term, oterm;
 	struct sigaction sa, savealrm, saveint, savehup, savequit, saveterm;
@@ -68,12 +68,20 @@ restart:
 	 * Read and write to /dev/tty if available.  If not, read from
 	 * stdin and write to stderr unless a tty is required.
 	 */
-	if ((flags & RPP_STDIN) ||
-	    (input = output = _open(_PATH_TTY, O_RDWR | O_CLOEXEC)) == -1) {
-		if (flags & RPP_REQUIRE_TTY) {
-			errno = ENOTTY;
-			return(NULL);
+	input_is_tty = 0;
+	if (!(flags & RPP_STDIN)) {
+        	input = output = _open(_PATH_TTY, O_RDWR | O_CLOEXEC);
+		if (input == -1) {
+			if (flags & RPP_REQUIRE_TTY) {
+				errno = ENOTTY;
+				return(NULL);
+			}
+			input = STDIN_FILENO;
+			output = STDERR_FILENO;
+		} else {
+			input_is_tty = 1;
 		}
+	} else {
 		input = STDIN_FILENO;
 		output = STDERR_FILENO;
 	}
@@ -83,7 +91,7 @@ restart:
 	 * If we are using a tty but are not the foreground pgrp this will
 	 * generate SIGTTOU, so do it *before* installing the signal handlers.
 	 */
-	if (input != STDIN_FILENO && tcgetattr(input, &oterm) == 0) {
+	if (input_is_tty && tcgetattr(input, &oterm) == 0) {
 		memcpy(&term, &oterm, sizeof(term));
 		if (!(flags & RPP_ECHO_ON))
 			term.c_lflag &= ~(ECHO | ECHONL);
@@ -152,7 +160,7 @@ restart:
 	(void)__libc_sigaction(SIGTSTP, &savetstp, NULL);
 	(void)__libc_sigaction(SIGTTIN, &savettin, NULL);
 	(void)__libc_sigaction(SIGTTOU, &savettou, NULL);
-	if (input != STDIN_FILENO)
+	if (input_is_tty)
 		(void)_close(input);
 
 	/*