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From af0faf666c5008e54dfe43684f210e3581ff1bca Mon Sep 17 00:00:00 2001
From: ikerexxe <ipedrosa@redhat.com>
Date: Tue, 16 Jun 2020 14:32:36 +0200
Subject: [PATCH] pam_unix: avoid determining if user exists
Taking a look at the time for the password prompt to appear it was
possible to determine if a user existed in a system. Solved it by
matching the runtime until the password prompt was shown by always
checking the password hash for an existing and a non-existing user.
Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=1629598
---
modules/pam_unix/passverify.c | 6 ++++++
modules/pam_unix/support.c | 33 ++++++++++++++++++++++++++-------
2 files changed, 32 insertions(+), 7 deletions(-)
diff --git a/modules/pam_unix/passverify.c b/modules/pam_unix/passverify.c
index a571b4f7..7455eae6 100644
--- a/modules/pam_unix/passverify.c
+++ b/modules/pam_unix/passverify.c
@@ -1096,6 +1096,12 @@ helper_verify_password(const char *name, const char *p, int nullok)
if (pwd == NULL || hash == NULL) {
helper_log_err(LOG_NOTICE, "check pass; user unknown");
retval = PAM_USER_UNKNOWN;
+ } else if (p[0] == '\0' && nullok) {
+ if (hash[0] == '\0') {
+ retval = PAM_SUCCESS;
+ } else {
+ retval = PAM_AUTH_ERR;
+ }
} else {
retval = verify_pwd_hash(p, hash, nullok);
}
diff --git a/modules/pam_unix/support.c b/modules/pam_unix/support.c
index 41db1f04..dc67238c 100644
--- a/modules/pam_unix/support.c
+++ b/modules/pam_unix/support.c
@@ -601,6 +601,8 @@ _unix_blankpasswd (pam_handle_t *pamh, unsigned long long ctrl, const char *name
char *salt = NULL;
int daysleft;
int retval;
+ int execloop = 1;
+ int nonexistent = 1;
D(("called"));
@@ -624,14 +626,31 @@ _unix_blankpasswd (pam_handle_t *pamh, unsigned long long ctrl, const char *name
/* UNIX passwords area */
- retval = get_pwd_hash(pamh, name, &pwd, &salt);
+ /*
+ * Execute this loop twice: one checking the password hash of an existing
+ * user and another one for a non-existing user. This way the runtimes
+ * are equal, making it more difficult to differentiate existing from
+ * non-existing users.
+ */
+ while (execloop) {
+ retval = get_pwd_hash(pamh, name, &pwd, &salt);
- if (retval == PAM_UNIX_RUN_HELPER) {
- /* salt will not be set here so we can return immediately */
- if (_unix_run_helper_binary(pamh, NULL, ctrl, name) == PAM_SUCCESS)
- return 1;
- else
- return 0;
+ if (retval == PAM_UNIX_RUN_HELPER) {
+ execloop = 0;
+ if(nonexistent) {
+ get_pwd_hash(pamh, "pam_unix_non_existent:", &pwd, &salt);
+ }
+ /* salt will not be set here so we can return immediately */
+ if (_unix_run_helper_binary(pamh, NULL, ctrl, name) == PAM_SUCCESS)
+ return 1;
+ else
+ return 0;
+ } else if (retval == PAM_USER_UNKNOWN) {
+ name = "root";
+ nonexistent = 0;
+ } else {
+ execloop = 0;
+ }
}
/* Does this user have a password? */
|
