From 18a2ccd22d53040df60d55203a86d67993091856 Mon Sep 17 00:00:00 2001 From: Maxim Sobolev Date: Sun, 24 Jan 2016 22:20:13 +0000 Subject: [PATCH] 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,0x100002,0x165f030) 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,0x100002,0x165f030) 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 --- lib/libc/gen/readpassphrase.c | 24 ++++++++++++++++-------- 1 file changed, 16 insertions(+), 8 deletions(-) diff --git a/lib/libc/gen/readpassphrase.c b/lib/libc/gen/readpassphrase.c index 60051a189e57..0961fbb35a8b 100644 --- a/lib/libc/gen/readpassphrase.c +++ b/lib/libc/gen/readpassphrase.c @@ -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 @@ readpassphrase(const char *prompt, char *buf, size_t bufsiz, int flags) * 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 @@ readpassphrase(const char *prompt, char *buf, size_t bufsiz, int flags) * 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 @@ readpassphrase(const char *prompt, char *buf, size_t bufsiz, int flags) (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); /*