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key_load_private() ignores the passphrase argument if the private key

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is unencrypted.  This defeats the nullok check, because it means a
non-null passphrase will successfully unlock the key.

To address this, try at first to load the key without a passphrase.
If this succeeds and the user provided a non-empty passphrase *or*
nullok is false, reject the key.

MFC after:	1 week
Noticed by:	Guy Helmer <guy.helmer@palisadesystems.com>
This commit is contained in:
des 2011-11-20 15:18:49 +00:00
parent 4de38879e5
commit bf5f03ca46
1 changed files with 18 additions and 7 deletions
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23
lib/libpam/modules/pam_ssh/pam_ssh.c
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@ -93,7 +93,8 @@ static char *const pam_ssh_agent_envp[] = { NULL };
* struct pam_ssh_key containing the key and its comment.
*/
static struct pam_ssh_key *
pam_ssh_load_key(const char *dir, const char *kfn, const char *passphrase)
pam_ssh_load_key(const char *dir, const char *kfn, const char *passphrase,
int nullok)
{
struct pam_ssh_key *psk;
char fn[PATH_MAX];
@ -103,6 +104,20 @@ pam_ssh_load_key(const char *dir, const char *kfn, const char *passphrase)
if (snprintf(fn, sizeof(fn), "%s/%s", dir, kfn) > (int)sizeof(fn))
return (NULL);
comment = NULL;
/*
* If the key is unencrypted, OpenSSL ignores the passphrase, so
* it will seem like the user typed in the right one. This allows
* a user to circumvent nullok by providing a dummy passphrase.
* Verify that the key really *is* encrypted by trying to load it
* with an empty passphrase, and if the key is not encrypted,
* accept only an empty passphrase.
*/
key = key_load_private(fn, NULL, &comment);
if (key != NULL && !(*passphrase == '\0' && nullok)) {
key_free(key);
return (NULL);
}
if (key == NULL)
key = key_load_private(fn, passphrase, &comment);
if (key == NULL) {
openpam_log(PAM_LOG_DEBUG, "failed to load key from %s", fn);
@ -170,9 +185,6 @@ pam_sm_authenticate(pam_handle_t *pamh, int flags __unused,
if (pam_err != PAM_SUCCESS)
return (pam_err);
if (*passphrase == '\0' && !nullok)
goto skip_keys;
/* switch to user credentials */
pam_err = openpam_borrow_cred(pamh, pwd);
if (pam_err != PAM_SUCCESS)
@ -180,7 +192,7 @@ pam_sm_authenticate(pam_handle_t *pamh, int flags __unused,
/* try to load keys from all keyfiles we know of */
for (kfn = pam_ssh_keyfiles; *kfn != NULL; ++kfn) {
psk = pam_ssh_load_key(pwd->pw_dir, *kfn, passphrase);
psk = pam_ssh_load_key(pwd->pw_dir, *kfn, passphrase, nullok);
if (psk != NULL) {
pam_set_data(pamh, *kfn, psk, pam_ssh_free_key);
++nkeys;
@ -190,7 +202,6 @@ pam_sm_authenticate(pam_handle_t *pamh, int flags __unused,
/* switch back to arbitrator credentials */
openpam_restore_cred(pamh);
skip_keys:
/*
* If we tried an old token and didn't get anything, and
* try_first_pass was specified, try again after prompting the