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From af0faf666c5008e54dfe43684f210e3581ff1bca Mon Sep 17 00:00:00 2001
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From: ikerexxe <ipedrosa@redhat.com>
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Date: Tue, 16 Jun 2020 14:32:36 +0200
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Subject: [PATCH 1/2] pam_unix: avoid determining if user exists
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Taking a look at the time for the password prompt to appear it was
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possible to determine if a user existed in a system. Solved it by
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matching the runtime until the password prompt was shown by always
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checking the password hash for an existing and a non-existing user.
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Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=1629598
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---
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modules/pam_unix/passverify.c | 6 ++++++
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modules/pam_unix/support.c | 33 ++++++++++++++++++++++++++-------
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2 files changed, 32 insertions(+), 7 deletions(-)
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diff --git a/modules/pam_unix/passverify.c b/modules/pam_unix/passverify.c
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index a571b4f7..7455eae6 100644
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--- a/modules/pam_unix/passverify.c
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+++ b/modules/pam_unix/passverify.c
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@@ -1096,6 +1096,12 @@ helper_verify_password(const char *name, const char *p, int nullok)
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if (pwd == NULL || hash == NULL) {
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helper_log_err(LOG_NOTICE, "check pass; user unknown");
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retval = PAM_USER_UNKNOWN;
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+ } else if (p[0] == '\0' && nullok) {
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+ if (hash[0] == '\0') {
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+ retval = PAM_SUCCESS;
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+ } else {
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+ retval = PAM_AUTH_ERR;
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+ }
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} else {
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retval = verify_pwd_hash(p, hash, nullok);
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}
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diff --git a/modules/pam_unix/support.c b/modules/pam_unix/support.c
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index 41db1f04..dc67238c 100644
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--- a/modules/pam_unix/support.c
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+++ b/modules/pam_unix/support.c
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@@ -601,6 +601,8 @@ _unix_blankpasswd (pam_handle_t *pamh, unsigned long long ctrl, const char *name
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char *salt = NULL;
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int daysleft;
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int retval;
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+ int execloop = 1;
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+ int nonexistent = 1;
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D(("called"));
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@@ -624,14 +626,31 @@ _unix_blankpasswd (pam_handle_t *pamh, unsigned long long ctrl, const char *name
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/* UNIX passwords area */
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- retval = get_pwd_hash(pamh, name, &pwd, &salt);
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+ /*
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+ * Execute this loop twice: one checking the password hash of an existing
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+ * user and another one for a non-existing user. This way the runtimes
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+ * are equal, making it more difficult to differentiate existing from
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+ * non-existing users.
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+ */
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+ while (execloop) {
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+ retval = get_pwd_hash(pamh, name, &pwd, &salt);
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- if (retval == PAM_UNIX_RUN_HELPER) {
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- /* salt will not be set here so we can return immediately */
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- if (_unix_run_helper_binary(pamh, NULL, ctrl, name) == PAM_SUCCESS)
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- return 1;
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- else
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- return 0;
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+ if (retval == PAM_UNIX_RUN_HELPER) {
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+ execloop = 0;
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+ if(nonexistent) {
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+ get_pwd_hash(pamh, "pam_unix_non_existent:", &pwd, &salt);
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+ }
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+ /* salt will not be set here so we can return immediately */
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+ if (_unix_run_helper_binary(pamh, NULL, ctrl, name) == PAM_SUCCESS)
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+ return 1;
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+ else
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+ return 0;
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+ } else if (retval == PAM_USER_UNKNOWN) {
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+ name = "root";
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+ nonexistent = 0;
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+ } else {
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+ execloop = 0;
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+ }
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}
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/* Does this user have a password? */
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--
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2.26.2
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From 0e9b286afe1224b91ff00936058b084ad4b776e4 Mon Sep 17 00:00:00 2001
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From: ikerexxe <ipedrosa@redhat.com>
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Date: Tue, 16 Jun 2020 14:44:04 +0200
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Subject: [PATCH 2/2] pam_usertype: avoid determining if user exists
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Taking a look at the time for the password prompt to appear it was
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possible to determine if a user existed in a system. Solved it by
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matching the runtime until the password prompt was shown by always
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checking the password hash for an existing and a non-existing user.
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Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=1629598
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---
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modules/pam_usertype/pam_usertype.c | 3 +++
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1 file changed, 3 insertions(+)
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diff --git a/modules/pam_usertype/pam_usertype.c b/modules/pam_usertype/pam_usertype.c
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index 2807c306..d03b73b5 100644
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--- a/modules/pam_usertype/pam_usertype.c
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+++ b/modules/pam_usertype/pam_usertype.c
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@@ -139,8 +139,11 @@ pam_usertype_get_uid(struct pam_usertype_opts *opts,
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"error retrieving information about user %s", username);
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}
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+ pam_modutil_getpwnam(pamh, "root");
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+
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return PAM_USER_UNKNOWN;
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}
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+ pam_modutil_getpwnam(pamh, "pam_usertype_non_existent:");
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*_uid = pwd->pw_uid;
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--
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2.26.2
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