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Use a salted hash of the lock passphrase instead of plain
 text and do constant-time comparisons of it. Should prevent leaking any
 information about it via timing, pointed out by Ryan Castellucci.  Add a 0.1s
 incrementing delay for each failed unlock attempt up to 10s.  ok markus@
 (earlier version), djm@

Upstream-ID: c599fcc325aa1cc65496b25220b622d22208c85f
This commit is contained in:
dtucker@openbsd.org 2015-05-15 05:44:21 +00:00 committed by Damien Miller
parent d028d5d3a6
commit 9173d0fbe4
1 changed files with 40 additions and 13 deletions
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53
ssh-agent.c
View File

@ -1,4 +1,4 @@
/* $OpenBSD: ssh-agent.c,v 1.202 2015/04/24 06:26:49 jmc Exp $ */
/* $OpenBSD: ssh-agent.c,v 1.203 2015/05/15 05:44:21 dtucker Exp $ */
/*
* Author: Tatu Ylonen <ylo@cs.hut.fi>
* Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
@ -68,6 +68,7 @@
#include <time.h>
#include <string.h>
#include <unistd.h>
#include <util.h>
#include "key.h" /* XXX for typedef */
#include "buffer.h" /* XXX for typedef */
@ -140,8 +141,12 @@ char socket_name[PATH_MAX];
char socket_dir[PATH_MAX];
/* locking */
#define LOCK_SIZE 32
#define LOCK_SALT_SIZE 16
#define LOCK_ROUNDS 1
int locked = 0;
char *lock_passwd = NULL;
char lock_passwd[LOCK_SIZE];
char lock_salt[LOCK_SALT_SIZE];
extern char *__progname;
@ -660,23 +665,45 @@ send:
static void
process_lock_agent(SocketEntry *e, int lock)
{
int r, success = 0;
char *passwd;
int r, success = 0, delay;
char *passwd, passwdhash[LOCK_SIZE];
static u_int fail_count = 0;
size_t pwlen;
if ((r = sshbuf_get_cstring(e->request, &passwd, NULL)) != 0)
if ((r = sshbuf_get_cstring(e->request, &passwd, &pwlen)) != 0)
fatal("%s: buffer error: %s", __func__, ssh_err(r));
if (locked && !lock && strcmp(passwd, lock_passwd) == 0) {
locked = 0;
explicit_bzero(lock_passwd, strlen(lock_passwd));
free(lock_passwd);
lock_passwd = NULL;
success = 1;
if (pwlen == 0) {
debug("empty password not supported");
} else if (locked && !lock) {
if (bcrypt_pbkdf(passwd, pwlen, lock_salt, sizeof(lock_salt),
passwdhash, sizeof(passwdhash), LOCK_ROUNDS) < 0)
fatal("bcrypt_pbkdf");
if (timingsafe_bcmp(passwdhash, lock_passwd, LOCK_SIZE) == 0) {
debug("agent unlocked");
locked = 0;
fail_count = 0;
explicit_bzero(lock_passwd, sizeof(lock_passwd));
success = 1;
} else {
/* delay in 0.1s increments up to 10s */
if (fail_count < 100)
fail_count++;
delay = 100000 * fail_count;
debug("unlock failed, delaying %0.1lf seconds",
(double)delay/1000000);
usleep(delay);
}
explicit_bzero(passwdhash, sizeof(passwdhash));
} else if (!locked && lock) {
debug("agent locked");
locked = 1;
lock_passwd = xstrdup(passwd);
arc4random_buf(lock_salt, sizeof(lock_salt));
if (bcrypt_pbkdf(passwd, pwlen, lock_salt, sizeof(lock_salt),
lock_passwd, sizeof(lock_passwd), LOCK_ROUNDS) < 0)
fatal("bcrypt_pbkdf");
success = 1;
}
explicit_bzero(passwd, strlen(passwd));
explicit_bzero(passwd, pwlen);
free(passwd);
send_status(e, success);
}