File 0001-Fix-CVE-FIXME-Trusting-client-supplied-UID.patch of Package polkit.9830
From b77e3f0c13ac008905ad2a867c63f766af43ea95 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Miloslav=20Trma=C4=8D?= <mitr@redhat.com>
Date: Mon, 25 Jun 2018 19:24:06 +0200
Subject: [PATCH] Fix CVE-FIXME: Trusting client-supplied UID
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit
As part of CVE-2013-4288, the D-Bus clients were allowed (and
encouraged) to submit the UID of the subject of authorization checks
to avoid races against UID changes (notably using executables
set-UID to root).
However, that also allowed any client to submit an arbitrary UID, and
that could be used to bypass "can only ask about / affect the same UID"
checks in CheckAuthorization / RegisterAuthenticationAgent /
UnregisterAuthenticationAgent. This allowed an attacker:
- With CheckAuthorization, to cause the registered authentication
agent in victim's session to pop up a dialog, or to determine whether
the victim currently has a temporary authorization to perform an
operation.
(In principle, the attacker can also determine whether JavaScript
rules allow the victim process to perform an operatin; however,
usually rules base their decisions on information deterined from
the supplied UID, so the attacker usually won't learn anything new.)
- With RegisterAuthenticationAgent, to prevent the victim's
authentication agent to work (for a specific victim process),
or to learn about which operations requiring authorization
the victim is attempting.
To fix this, expose internal _polkit_unix_process_get_owner() /
obsolete polkit_unix_process_get_owner() as a private
polkit_unix_process_get_racy_uid__() (being more explicit about the
dangers on relying on it), and use it in
polkit_backend_session_monitor_get_user_for_subject() to return
a boolean indicating whether the subject UID may be caller-chosen.
Then, in the permission checks that require the subject to be
equal to the caller, fail on caller-chosen UIDs (and continue
through the pre-existing code paths which allow root, or root-designated
server processes, to ask about arbitrary subjects.)
Signed-off-by: Miloslav Trmač <mitr@redhat.com>
---
src/polkit/polkitprivate.h | 2 +
src/polkit/polkitunixprocess.c | 61 ++++++++++++++++---
.../polkitbackendinteractiveauthority.c | 39 +++++++-----
.../polkitbackendsessionmonitor-systemd.c | 38 ++++++++++--
.../polkitbackendsessionmonitor.c | 40 ++++++++++--
.../polkitbackendsessionmonitor.h | 1 +
6 files changed, 148 insertions(+), 33 deletions(-)
diff --git a/src/polkit/polkitprivate.h b/src/polkit/polkitprivate.h
index 9f07063..c80142d 100644
--- a/src/polkit/polkitprivate.h
+++ b/src/polkit/polkitprivate.h
@@ -44,6 +44,8 @@ GVariant *polkit_action_description_to_gvariant (PolkitActionDescription *action
GVariant *polkit_subject_to_gvariant (PolkitSubject *subject);
GVariant *polkit_identity_to_gvariant (PolkitIdentity *identity);
+gint polkit_unix_process_get_racy_uid__ (PolkitUnixProcess *process, GError **error);
+
PolkitSubject *polkit_subject_new_for_gvariant (GVariant *variant, GError **error);
PolkitIdentity *polkit_identity_new_for_gvariant (GVariant *variant, GError **error);
diff --git a/src/polkit/polkitunixprocess.c b/src/polkit/polkitunixprocess.c
index d4ebf50..972b777 100644
--- a/src/polkit/polkitunixprocess.c
+++ b/src/polkit/polkitunixprocess.c
@@ -56,6 +56,14 @@
* To uniquely identify processes, both the process id and the start
* time of the process (a monotonic increasing value representing the
* time since the kernel was started) is used.
+ *
+ * NOTE: This object stores, and provides access to, the real UID of the
+ * process. That value can change over time (with set*uid*(2) and exec*(2)).
+ * Checks whether an operation is allowed need to take care to use the UID
+ * value as of the time when the operation was made (or, following the open()
+ * privilege check model, when the connection making the operation possible
+ * was initiated). That is usually done by initializing this with
+ * polkit_unix_process_new_for_owner() with trusted data.
*/
/**
@@ -90,9 +98,6 @@ static void subject_iface_init (PolkitSubjectIface *subject_iface);
static guint64 get_start_time_for_pid (gint pid,
GError **error);
-static gint _polkit_unix_process_get_owner (PolkitUnixProcess *process,
- GError **error);
-
#if defined(HAVE_FREEBSD) || defined(HAVE_NETBSD) || defined(HAVE_OPENBSD)
static gboolean get_kinfo_proc (gint pid,
#if defined(HAVE_NETBSD)
@@ -182,7 +187,7 @@ polkit_unix_process_constructed (GObject *object)
{
GError *error;
error = NULL;
- process->uid = _polkit_unix_process_get_owner (process, &error);
+ process->uid = polkit_unix_process_get_racy_uid__ (process, &error);
if (error != NULL)
{
process->uid = -1;
@@ -271,6 +276,12 @@ polkit_unix_process_class_init (PolkitUnixProcessClass *klass)
* Gets the user id for @process. Note that this is the real user-id,
* not the effective user-id.
*
+ * NOTE: The UID may change over time, so the returned value may not match the
+ * current state of the underlying process; or the UID may have been set by
+ * polkit_unix_process_new_for_owner() or polkit_unix_process_set_uid(),
+ * in which case it may not correspond to the actual UID of the referenced
+ * process at all (at any point in time).
+ *
* Returns: The user id for @process or -1 if unknown.
*/
gint
@@ -708,13 +719,20 @@ out:
return start_time;
}
-static gint
-_polkit_unix_process_get_owner (PolkitUnixProcess *process,
- GError **error)
+/*
+ * Private: Return the "current" UID. Note that this is inherently racy,
+ * and the value may already be obsolete by the time this function returns;
+ * this function only guarantees that the UID was valid at some point during
+ * its execution.
+ */
+gint
+polkit_unix_process_get_racy_uid__ (PolkitUnixProcess *process,
+ GError **error)
{
gint result;
gchar *contents;
gchar **lines;
+ guint64 start_time;
#if defined(HAVE_FREEBSD) || defined(HAVE_OPENBSD)
struct kinfo_proc p;
#elif defined(HAVE_NETBSD)
@@ -722,6 +740,7 @@ _polkit_unix_process_get_owner (PolkitUnixProcess *process,
#else
gchar filename[64];
guint n;
+ GError *local_error;
#endif
g_return_val_if_fail (POLKIT_IS_UNIX_PROCESS (process), 0);
@@ -745,8 +764,10 @@ _polkit_unix_process_get_owner (PolkitUnixProcess *process,
#if defined(HAVE_FREEBSD)
result = p.ki_uid;
+ start_time = (guint64) p.ki_start.tv_sec;
#else
result = p.p_uid;
+ start_time = (guint64) p.p_ustart_sec;
#endif
#else
@@ -781,17 +802,37 @@ _polkit_unix_process_get_owner (PolkitUnixProcess *process,
else
{
result = real_uid;
- goto out;
+ goto found;
}
}
-
g_set_error (error,
POLKIT_ERROR,
POLKIT_ERROR_FAILED,
"Didn't find any line starting with `Uid:' in file %s",
filename);
+ goto out;
+
+found:
+ /* The UID and start time are, sadly, not available in a single file. So,
+ * read the UID first, and then the start time; if the start time is the same
+ * before and after reading the UID, it couldn't have changed.
+ */
+ local_error = NULL;
+ start_time = get_start_time_for_pid (process->pid, &local_error);
+ if (local_error != NULL)
+ {
+ g_propagate_error (error, local_error);
+ goto out;
+ }
#endif
+ if (process->start_time != start_time)
+ {
+ g_set_error (error, POLKIT_ERROR, POLKIT_ERROR_FAILED,
+ "process with PID %d has been replaced", process->pid);
+ goto out;
+ }
+
out:
g_strfreev (lines);
g_free (contents);
@@ -810,5 +851,5 @@ gint
polkit_unix_process_get_owner (PolkitUnixProcess *process,
GError **error)
{
- return _polkit_unix_process_get_owner (process, error);
+ return polkit_unix_process_get_racy_uid__ (process, error);
}
diff --git a/src/polkitbackend/polkitbackendinteractiveauthority.c b/src/polkitbackend/polkitbackendinteractiveauthority.c
index 1cd60d3..cb6fdab 100644
--- a/src/polkitbackend/polkitbackendinteractiveauthority.c
+++ b/src/polkitbackend/polkitbackendinteractiveauthority.c
@@ -575,7 +575,7 @@ log_result (PolkitBackendInteractiveAuthority *authority,
if (polkit_authorization_result_get_is_authorized (result))
log_result_str = "ALLOWING";
- user_of_subject = polkit_backend_session_monitor_get_user_for_subject (priv->session_monitor, subject, NULL);
+ user_of_subject = polkit_backend_session_monitor_get_user_for_subject (priv->session_monitor, subject, NULL, NULL);
subject_str = polkit_subject_to_string (subject);
@@ -847,6 +847,7 @@ polkit_backend_interactive_authority_check_authorization (PolkitBackendAuthority
gchar *subject_str;
PolkitIdentity *user_of_caller;
PolkitIdentity *user_of_subject;
+ gboolean user_of_subject_matches;
gchar *user_of_caller_str;
gchar *user_of_subject_str;
PolkitAuthorizationResult *result;
@@ -892,7 +893,7 @@ polkit_backend_interactive_authority_check_authorization (PolkitBackendAuthority
action_id);
user_of_caller = polkit_backend_session_monitor_get_user_for_subject (priv->session_monitor,
- caller,
+ caller, NULL,
&error);
if (error != NULL)
{
@@ -907,7 +908,7 @@ polkit_backend_interactive_authority_check_authorization (PolkitBackendAuthority
g_debug (" user of caller is %s", user_of_caller_str);
user_of_subject = polkit_backend_session_monitor_get_user_for_subject (priv->session_monitor,
- subject,
+ subject, &user_of_subject_matches,
&error);
if (error != NULL)
{
@@ -937,7 +938,10 @@ polkit_backend_interactive_authority_check_authorization (PolkitBackendAuthority
* We only allow this if, and only if,
*
* - processes may check for another process owned by the *same* user but not
- * if details are passed (otherwise you'd be able to spoof the dialog)
+ * if details are passed (otherwise you'd be able to spoof the dialog);
+ * the caller supplies the user_of_subject value, so we additionally
+ * require it to match at least at one point in time (via
+ * user_of_subject_matches).
*
* - processes running as uid 0 may check anything and pass any details
*
@@ -945,7 +949,9 @@ polkit_backend_interactive_authority_check_authorization (PolkitBackendAuthority
* then any uid referenced by that annotation is also allowed to check
* to check anything and pass any details
*/
- if (!polkit_identity_equal (user_of_caller, user_of_subject) || has_details)
+ if (!user_of_subject_matches
+ || !polkit_identity_equal (user_of_caller, user_of_subject)
+ || has_details)
{
if (!may_identity_check_authorization (interactive_authority, action_id, user_of_caller))
{
@@ -1110,9 +1116,10 @@ check_authorization_sync (PolkitBackendAuthority *authority,
goto out;
}
- /* every subject has a user */
+ /* every subject has a user; this is supplied by the client, so we rely
+ * on the caller to validate its acceptability. */
user_of_subject = polkit_backend_session_monitor_get_user_for_subject (priv->session_monitor,
- subject,
+ subject, NULL,
error);
if (user_of_subject == NULL)
goto out;
@@ -2480,6 +2487,7 @@ polkit_backend_interactive_authority_register_authentication_agent (PolkitBacken
PolkitSubject *session_for_caller;
PolkitIdentity *user_of_caller;
PolkitIdentity *user_of_subject;
+ gboolean user_of_subject_matches;
AuthenticationAgent *agent;
gboolean ret;
gchar *caller_cmdline;
@@ -2532,7 +2540,7 @@ polkit_backend_interactive_authority_register_authentication_agent (PolkitBacken
goto out;
}
- user_of_caller = polkit_backend_session_monitor_get_user_for_subject (priv->session_monitor, caller, NULL);
+ user_of_caller = polkit_backend_session_monitor_get_user_for_subject (priv->session_monitor, caller, NULL, NULL);
if (user_of_caller == NULL)
{
g_set_error (error,
@@ -2541,7 +2549,7 @@ polkit_backend_interactive_authority_register_authentication_agent (PolkitBacken
"Cannot determine user of caller");
goto out;
}
- user_of_subject = polkit_backend_session_monitor_get_user_for_subject (priv->session_monitor, subject, NULL);
+ user_of_subject = polkit_backend_session_monitor_get_user_for_subject (priv->session_monitor, subject, &user_of_subject_matches, NULL);
if (user_of_subject == NULL)
{
g_set_error (error,
@@ -2550,7 +2558,8 @@ polkit_backend_interactive_authority_register_authentication_agent (PolkitBacken
"Cannot determine user of subject");
goto out;
}
- if (!polkit_identity_equal (user_of_caller, user_of_subject))
+ if (!user_of_subject_matches
+ || !polkit_identity_equal (user_of_caller, user_of_subject))
{
if (identity_is_root_user (user_of_caller))
{
@@ -2643,6 +2652,7 @@ polkit_backend_interactive_authority_unregister_authentication_agent (PolkitBack
PolkitSubject *session_for_caller;
PolkitIdentity *user_of_caller;
PolkitIdentity *user_of_subject;
+ gboolean user_of_subject_matches;
AuthenticationAgent *agent;
gboolean ret;
gchar *scope_str;
@@ -2691,7 +2701,7 @@ polkit_backend_interactive_authority_unregister_authentication_agent (PolkitBack
goto out;
}
- user_of_caller = polkit_backend_session_monitor_get_user_for_subject (priv->session_monitor, caller, NULL);
+ user_of_caller = polkit_backend_session_monitor_get_user_for_subject (priv->session_monitor, caller, NULL, NULL);
if (user_of_caller == NULL)
{
g_set_error (error,
@@ -2700,7 +2710,7 @@ polkit_backend_interactive_authority_unregister_authentication_agent (PolkitBack
"Cannot determine user of caller");
goto out;
}
- user_of_subject = polkit_backend_session_monitor_get_user_for_subject (priv->session_monitor, subject, NULL);
+ user_of_subject = polkit_backend_session_monitor_get_user_for_subject (priv->session_monitor, subject, &user_of_subject_matches, NULL);
if (user_of_subject == NULL)
{
g_set_error (error,
@@ -2709,7 +2719,8 @@ polkit_backend_interactive_authority_unregister_authentication_agent (PolkitBack
"Cannot determine user of subject");
goto out;
}
- if (!polkit_identity_equal (user_of_caller, user_of_subject))
+ if (!user_of_subject_matches
+ || !polkit_identity_equal (user_of_caller, user_of_subject))
{
if (identity_is_root_user (user_of_caller))
{
@@ -2819,7 +2830,7 @@ polkit_backend_interactive_authority_authentication_agent_response (PolkitBacken
identity_str);
user_of_caller = polkit_backend_session_monitor_get_user_for_subject (priv->session_monitor,
- caller,
+ caller, NULL,
error);
if (user_of_caller == NULL)
goto out;
diff --git a/src/polkitbackend/polkitbackendsessionmonitor-systemd.c b/src/polkitbackend/polkitbackendsessionmonitor-systemd.c
index 2a6c739..b00cdbd 100644
--- a/src/polkitbackend/polkitbackendsessionmonitor-systemd.c
+++ b/src/polkitbackend/polkitbackendsessionmonitor-systemd.c
@@ -29,6 +29,7 @@
#include <stdlib.h>
#include <polkit/polkit.h>
+#include <polkit/polkitprivate.h>
#include "polkitbackendsessionmonitor.h"
/* <internal>
@@ -246,26 +247,40 @@ polkit_backend_session_monitor_get_sessions (PolkitBackendSessionMonitor *monito
* polkit_backend_session_monitor_get_user:
* @monitor: A #PolkitBackendSessionMonitor.
* @subject: A #PolkitSubject.
+ * @result_matches: If not %NULL, set to indicate whether the return value matches current (RACY) state.
* @error: Return location for error.
*
* Gets the user corresponding to @subject or %NULL if no user exists.
*
+ * NOTE: For a #PolkitUnixProcess, the UID is read from @subject (which may
+ * come from e.g. a D-Bus client), so it may not correspond to the actual UID
+ * of the referenced process (at any point in time). This is indicated by
+ * setting @result_matches to %FALSE; the caller may reject such subjects or
+ * require additional privileges. @result_matches == %TRUE only indicates that
+ * the UID matched the underlying process at ONE point in time, it may not match
+ * later.
+ *
* Returns: %NULL if @error is set otherwise a #PolkitUnixUser that should be freed with g_object_unref().
*/
PolkitIdentity *
polkit_backend_session_monitor_get_user_for_subject (PolkitBackendSessionMonitor *monitor,
PolkitSubject *subject,
+ gboolean *result_matches,
GError **error)
{
PolkitIdentity *ret;
- guint32 uid;
+ gboolean matches;
ret = NULL;
+ matches = FALSE;
if (POLKIT_IS_UNIX_PROCESS (subject))
{
- uid = polkit_unix_process_get_uid (POLKIT_UNIX_PROCESS (subject));
- if ((gint) uid == -1)
+ gint subject_uid, current_uid;
+ GError *local_error;
+
+ subject_uid = polkit_unix_process_get_uid (POLKIT_UNIX_PROCESS (subject));
+ if (subject_uid == -1)
{
g_set_error (error,
POLKIT_ERROR,
@@ -273,14 +288,24 @@ polkit_backend_session_monitor_get_user_for_subject (PolkitBackendSessionMonitor
"Unix process subject does not have uid set");
goto out;
}
- ret = polkit_unix_user_new (uid);
+ local_error = NULL;
+ current_uid = polkit_unix_process_get_racy_uid__ (POLKIT_UNIX_PROCESS (subject), &local_error);
+ if (local_error != NULL)
+ {
+ g_propagate_error (error, local_error);
+ goto out;
+ }
+ ret = polkit_unix_user_new (subject_uid);
+ matches = (subject_uid == current_uid);
}
else if (POLKIT_IS_SYSTEM_BUS_NAME (subject))
{
ret = (PolkitIdentity*)polkit_system_bus_name_get_user_sync (POLKIT_SYSTEM_BUS_NAME (subject), NULL, error);
+ matches = TRUE;
}
else if (POLKIT_IS_UNIX_SESSION (subject))
{
+ uid_t uid;
if (sd_session_get_uid (polkit_unix_session_get_session_id (POLKIT_UNIX_SESSION (subject)), &uid) < 0)
{
@@ -292,9 +317,14 @@ polkit_backend_session_monitor_get_user_for_subject (PolkitBackendSessionMonitor
}
ret = polkit_unix_user_new (uid);
+ matches = TRUE;
}
out:
+ if (result_matches != NULL)
+ {
+ *result_matches = matches;
+ }
return ret;
}
diff --git a/src/polkitbackend/polkitbackendsessionmonitor.c b/src/polkitbackend/polkitbackendsessionmonitor.c
index e1a9ab3..ed30755 100644
--- a/src/polkitbackend/polkitbackendsessionmonitor.c
+++ b/src/polkitbackend/polkitbackendsessionmonitor.c
@@ -27,6 +27,7 @@
#include <glib/gstdio.h>
#include <polkit/polkit.h>
+#include <polkit/polkitprivate.h>
#include "polkitbackendsessionmonitor.h"
#define CKDB_PATH "/var/run/ConsoleKit/database"
@@ -273,28 +274,40 @@ polkit_backend_session_monitor_get_sessions (PolkitBackendSessionMonitor *monito
* polkit_backend_session_monitor_get_user:
* @monitor: A #PolkitBackendSessionMonitor.
* @subject: A #PolkitSubject.
+ * @result_matches: If not %NULL, set to indicate whether the return value matches current (RACY) state.
* @error: Return location for error.
*
* Gets the user corresponding to @subject or %NULL if no user exists.
*
+ * NOTE: For a #PolkitUnixProcess, the UID is read from @subject (which may
+ * come from e.g. a D-Bus client), so it may not correspond to the actual UID
+ * of the referenced process (at any point in time). This is indicated by
+ * setting @result_matches to %FALSE; the caller may reject such subjects or
+ * require additional privileges. @result_matches == %TRUE only indicates that
+ * the UID matched the underlying process at ONE point in time, it may not match
+ * later.
+ *
* Returns: %NULL if @error is set otherwise a #PolkitUnixUser that should be freed with g_object_unref().
*/
PolkitIdentity *
polkit_backend_session_monitor_get_user_for_subject (PolkitBackendSessionMonitor *monitor,
PolkitSubject *subject,
+ gboolean *result_matches,
GError **error)
{
PolkitIdentity *ret;
+ gboolean matches;
GError *local_error;
- gchar *group;
- guint32 uid;
ret = NULL;
+ matches = FALSE;
if (POLKIT_IS_UNIX_PROCESS (subject))
{
- uid = polkit_unix_process_get_uid (POLKIT_UNIX_PROCESS (subject));
- if ((gint) uid == -1)
+ gint subject_uid, current_uid;
+
+ subject_uid = polkit_unix_process_get_uid (POLKIT_UNIX_PROCESS (subject));
+ if (subject_uid == -1)
{
g_set_error (error,
POLKIT_ERROR,
@@ -302,14 +315,26 @@ polkit_backend_session_monitor_get_user_for_subject (PolkitBackendSessionMonitor
"Unix process subject does not have uid set");
goto out;
}
- ret = polkit_unix_user_new (uid);
+ local_error = NULL;
+ current_uid = polkit_unix_process_get_racy_uid__ (POLKIT_UNIX_PROCESS (subject), &local_error);
+ if (local_error != NULL)
+ {
+ g_propagate_error (error, local_error);
+ goto out;
+ }
+ ret = polkit_unix_user_new (subject_uid);
+ matches = (subject_uid == current_uid);
}
else if (POLKIT_IS_SYSTEM_BUS_NAME (subject))
{
ret = (PolkitIdentity*)polkit_system_bus_name_get_user_sync (POLKIT_SYSTEM_BUS_NAME (subject), NULL, error);
+ matches = TRUE;
}
else if (POLKIT_IS_UNIX_SESSION (subject))
{
+ gint uid;
+ gchar *group;
+
if (!ensure_database (monitor, error))
{
g_prefix_error (error, "Error getting user for session: Error ensuring CK database at " CKDB_PATH ": ");
@@ -328,9 +353,14 @@ polkit_backend_session_monitor_get_user_for_subject (PolkitBackendSessionMonitor
g_free (group);
ret = polkit_unix_user_new (uid);
+ matches = TRUE;
}
out:
+ if (result_matches != NULL)
+ {
+ *result_matches = matches;
+ }
return ret;
}
diff --git a/src/polkitbackend/polkitbackendsessionmonitor.h b/src/polkitbackend/polkitbackendsessionmonitor.h
index 8f8a2ca..3972326 100644
--- a/src/polkitbackend/polkitbackendsessionmonitor.h
+++ b/src/polkitbackend/polkitbackendsessionmonitor.h
@@ -47,6 +47,7 @@ GList *polkit_backend_session_monitor_get_sessions (Polkit
PolkitIdentity *polkit_backend_session_monitor_get_user_for_subject (PolkitBackendSessionMonitor *monitor,
PolkitSubject *subject,
+ gboolean *result_matches,
GError **error);
PolkitSubject *polkit_backend_session_monitor_get_session_for_subject (PolkitBackendSessionMonitor *monitor,
--
2.17.1
