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auth-pam: Check the user didn't change during PAM transaction #521

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auth-pam: Check the user didn't change during PAM transaction #521

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35 changes: 30 additions & 5 deletions auth-pam.c
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Original file line number Diff line number Diff line change
Expand Up @@ -467,6 +467,28 @@ sshpam_thread_conv(int n, sshpam_const struct pam_message **msg,
return (PAM_CONV_ERR);
}

static int
check_pam_user(Authctxt *authctxt)
{
const char *pam_user;

if (authctxt == NULL || authctxt->user == NULL)
fatal("%s: PAM authctxt user not initialized", __func__);

sshpam_err = pam_get_item(sshpam_handle,
PAM_USER, (sshpam_const void **) &pam_user);
if (sshpam_err != PAM_SUCCESS)
return sshpam_err;

if (pam_user == NULL || strcmp(authctxt->user, pam_user) != 0) {
debug("PAM: User '%s' does not match expected '%s'",
pam_user, authctxt->user);
return PAM_USER_UNKNOWN;
}

return PAM_SUCCESS;
}

/*
* Authentication thread.
*/
Expand Down Expand Up @@ -521,6 +543,9 @@ sshpam_thread(void *ctxtp)
sshpam_set_maxtries_reached(1);
if (sshpam_err != PAM_SUCCESS)
goto auth_fail;
sshpam_err = check_pam_user(sshpam_authctxt);
if (sshpam_err != PAM_SUCCESS)
goto auth_fail;

if (!do_pam_account()) {
sshpam_err = PAM_ACCT_EXPIRED;
Expand Down Expand Up @@ -686,8 +711,7 @@ sshpam_cleanup(void)
static int
sshpam_init(struct ssh *ssh, Authctxt *authctxt)
{
const char *pam_user, *user = authctxt->user;
const char **ptr_pam_user = &pam_user;
const char *user = authctxt->user;
int r;

if (options.pam_service_name == NULL)
Expand All @@ -706,9 +730,8 @@ sshpam_init(struct ssh *ssh, Authctxt *authctxt)
}
if (sshpam_handle != NULL) {
/* We already have a PAM context; check if the user matches */
sshpam_err = pam_get_item(sshpam_handle,
PAM_USER, (sshpam_const void **)ptr_pam_user);
if (sshpam_err == PAM_SUCCESS && strcmp(user, pam_user) == 0)
sshpam_err = check_pam_user(authctxt);
if (sshpam_err == PAM_SUCCESS)
return (0);
pam_end(sshpam_handle, sshpam_err);
sshpam_handle = NULL;
Expand Down Expand Up @@ -1378,6 +1401,8 @@ sshpam_auth_passwd(Authctxt *authctxt, const char *password)
sshpam_err = pam_authenticate(sshpam_handle, flags);
sshpam_password = NULL;
free(fake);
if (sshpam_err == PAM_SUCCESS)
sshpam_err = check_pam_user(authctxt);
if (sshpam_err == PAM_MAXTRIES)
sshpam_set_maxtries_reached(1);
if (sshpam_err == PAM_SUCCESS && authctxt->valid) {
Expand Down
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