From 46d1a01694268a86aa155a66c9cc757e8d136661 Mon Sep 17 00:00:00 2001 From: Colin Walters Date: Thu, 4 Jun 2015 12:15:18 -0400 Subject: [PATCH] CVE-XXX-XXXX: Use unpredictable cookie values, keep them secret Tavis noted that it'd be possible with a 32 bit counter for someone to cause the cookie to wrap by creating Authentication requests in a loop. Something important to note here is that wrapping of signed integers is undefined behavior in C, so we definitely want to fix that. All counter integers used in this patch are unsigned. See the comment above `authentication_agent_generate_cookie` for details, but basically we're now using a cookie of the form: - - - Which has multiple 64 bit counters, plus unpredictable random 128 bit integer ids (effectively UUIDs, but we're not calling them that because we don't need to be globally unique. We further ensure that the cookies are not visible to other processes by changing the setuid helper to accept them over standard input. This means that an attacker would have to guess both ids. In any case, the security hole here is better fixed with the other change to bind user id (uid) of the agent with cookie lookups, making cookie guessing worthless. Nevertheless, I think it's worth doing this change too, for defense in depth. Bug: https://bugs.freedesktop.org/show_bug.cgi?id=90832 Reported-by: Tavis Ormandy Signed-off-by: Colin Walters --- configure.ac | 2 +- src/polkitagent/polkitagenthelper-pam.c | 12 ++- src/polkitagent/polkitagenthelper-shadow.c | 12 ++- src/polkitagent/polkitagenthelperprivate.c | 33 ++++++++ src/polkitagent/polkitagenthelperprivate.h | 2 + src/polkitagent/polkitagentsession.c | 30 ++++--- .../polkitbackendinteractiveauthority.c | 99 +++++++++++++++++----- 7 files changed, 150 insertions(+), 40 deletions(-) diff --git a/configure.ac b/configure.ac index d9a97bb..91cc627 100644 --- a/configure.ac +++ b/configure.ac @@ -121,7 +121,7 @@ if test "x$GCC" = "xyes"; then changequote([,])dnl fi -PKG_CHECK_MODULES(GLIB, [gmodule-2.0 gio-2.0 >= 2.30.0]) +PKG_CHECK_MODULES(GLIB, [gmodule-2.0 gio-unix-2.0 >= 2.30.0]) AC_SUBST(GLIB_CFLAGS) AC_SUBST(GLIB_LIBS) AC_DEFINE([GLIB_VERSION_MIN_REQUIRED], [GLIB_VERSION_2_30], diff --git a/src/polkitagent/polkitagenthelper-pam.c b/src/polkitagent/polkitagenthelper-pam.c index 937386e..19062aa 100644 --- a/src/polkitagent/polkitagenthelper-pam.c +++ b/src/polkitagent/polkitagenthelper-pam.c @@ -65,7 +65,7 @@ main (int argc, char *argv[]) { int rc; const char *user_to_auth; - const char *cookie; + char *cookie = NULL; struct pam_conv pam_conversation; pam_handle_t *pam_h; const void *authed_user; @@ -97,7 +97,7 @@ main (int argc, char *argv[]) openlog ("polkit-agent-helper-1", LOG_CONS | LOG_PID, LOG_AUTHPRIV); /* check for correct invocation */ - if (argc != 3) + if (!(argc == 2 || argc == 3)) { syslog (LOG_NOTICE, "inappropriate use of helper, wrong number of arguments [uid=%d]", getuid ()); fprintf (stderr, "polkit-agent-helper-1: wrong number of arguments. This incident has been logged.\n"); @@ -105,7 +105,10 @@ main (int argc, char *argv[]) } user_to_auth = argv[1]; - cookie = argv[2]; + + cookie = read_cookie (argc, argv); + if (!cookie) + goto error; if (getuid () != 0) { @@ -203,6 +206,8 @@ main (int argc, char *argv[]) goto error; } + free (cookie); + #ifdef PAH_DEBUG fprintf (stderr, "polkit-agent-helper-1: successfully sent D-Bus message to PolicyKit daemon\n"); #endif /* PAH_DEBUG */ @@ -212,6 +217,7 @@ main (int argc, char *argv[]) return 0; error: + free (cookie); if (pam_h != NULL) pam_end (pam_h, rc); diff --git a/src/polkitagent/polkitagenthelper-shadow.c b/src/polkitagent/polkitagenthelper-shadow.c index a4f73ac..e877915 100644 --- a/src/polkitagent/polkitagenthelper-shadow.c +++ b/src/polkitagent/polkitagenthelper-shadow.c @@ -46,7 +46,7 @@ main (int argc, char *argv[]) { struct spwd *shadow; const char *user_to_auth; - const char *cookie; + char *cookie = NULL; time_t now; /* clear the entire environment to avoid attacks with @@ -67,7 +67,7 @@ main (int argc, char *argv[]) openlog ("polkit-agent-helper-1", LOG_CONS | LOG_PID, LOG_AUTHPRIV); /* check for correct invocation */ - if (argc != 3) + if (!(argc == 2 || argc == 3)) { syslog (LOG_NOTICE, "inappropriate use of helper, wrong number of arguments [uid=%d]", getuid ()); fprintf (stderr, "polkit-agent-helper-1: wrong number of arguments. This incident has been logged.\n"); @@ -86,7 +86,10 @@ main (int argc, char *argv[]) } user_to_auth = argv[1]; - cookie = argv[2]; + + cookie = read_cookie (argc, argv); + if (!cookie) + goto error; #ifdef PAH_DEBUG fprintf (stderr, "polkit-agent-helper-1: user to auth is '%s'.\n", user_to_auth); @@ -153,6 +156,8 @@ main (int argc, char *argv[]) goto error; } + free (cookie); + #ifdef PAH_DEBUG fprintf (stderr, "polkit-agent-helper-1: successfully sent D-Bus message to PolicyKit daemon\n"); #endif /* PAH_DEBUG */ @@ -162,6 +167,7 @@ main (int argc, char *argv[]) return 0; error: + free (cookie); fprintf (stdout, "FAILURE\n"); flush_and_wait (); return 1; diff --git a/src/polkitagent/polkitagenthelperprivate.c b/src/polkitagent/polkitagenthelperprivate.c index cfa77fc..6c881cc 100644 --- a/src/polkitagent/polkitagenthelperprivate.c +++ b/src/polkitagent/polkitagenthelperprivate.c @@ -23,6 +23,7 @@ #include "config.h" #include "polkitagenthelperprivate.h" #include +#include #include #include @@ -45,6 +46,38 @@ _polkit_clearenv (void) #endif +char * +read_cookie (int argc, char **argv) +{ + /* As part of CVE-XXX-XXXX, we started passing the cookie + * on standard input, to ensure it's not visible to other + * processes. However, to ensure that things continue + * to work if the setuid binary is upgraded while old + * agents are still running (this will be common with + * package managers), we support both modes. + */ + if (argc == 3) + return strdup (argv[2]); + else + { + char *ret = NULL; + size_t n = 0; + ssize_t r = getline (&ret, &n, stdin); + if (r == -1) + { + if (!feof (stdin)) + perror ("getline"); + free (ret); + return NULL; + } + else + { + g_strchomp (ret); + return ret; + } + } +} + gboolean send_dbus_message (const char *cookie, const char *user) { diff --git a/src/polkitagent/polkitagenthelperprivate.h b/src/polkitagent/polkitagenthelperprivate.h index aeca2c7..547fdcc 100644 --- a/src/polkitagent/polkitagenthelperprivate.h +++ b/src/polkitagent/polkitagenthelperprivate.h @@ -38,6 +38,8 @@ int _polkit_clearenv (void); +char *read_cookie (int argc, char **argv); + gboolean send_dbus_message (const char *cookie, const char *user); void flush_and_wait (); diff --git a/src/polkitagent/polkitagentsession.c b/src/polkitagent/polkitagentsession.c index f014773..8b93ad0 100644 --- a/src/polkitagent/polkitagentsession.c +++ b/src/polkitagent/polkitagentsession.c @@ -55,6 +55,7 @@ #include #include #include +#include #include #include "polkitagentmarshal.h" @@ -88,7 +89,7 @@ struct _PolkitAgentSession gchar *cookie; PolkitIdentity *identity; - int child_stdin; + GOutputStream *child_stdin; int child_stdout; GPid child_pid; @@ -129,7 +130,6 @@ G_DEFINE_TYPE (PolkitAgentSession, polkit_agent_session, G_TYPE_OBJECT); static void polkit_agent_session_init (PolkitAgentSession *session) { - session->child_stdin = -1; session->child_stdout = -1; } @@ -395,11 +395,7 @@ kill_helper (PolkitAgentSession *session) session->child_stdout = -1; } - if (session->child_stdin != -1) - { - g_warn_if_fail (close (session->child_stdin) == 0); - session->child_stdin = -1; - } + g_clear_object (&session->child_stdin); session->helper_is_running = FALSE; @@ -545,9 +541,9 @@ polkit_agent_session_response (PolkitAgentSession *session, add_newline = (response[response_len] != '\n'); - write (session->child_stdin, response, response_len); + (void) g_output_stream_write_all (session->child_stdin, response, response_len, NULL, NULL, NULL); if (add_newline) - write (session->child_stdin, newline, 1); + (void) g_output_stream_write_all (session->child_stdin, newline, 1, NULL, NULL, NULL); } /** @@ -567,8 +563,9 @@ polkit_agent_session_initiate (PolkitAgentSession *session) { uid_t uid; GError *error; - gchar *helper_argv[4]; + gchar *helper_argv[3]; struct passwd *passwd; + int stdin_fd = -1; g_return_if_fail (POLKIT_AGENT_IS_SESSION (session)); @@ -600,10 +597,8 @@ polkit_agent_session_initiate (PolkitAgentSession *session) helper_argv[0] = PACKAGE_PREFIX "/lib/polkit-1/polkit-agent-helper-1"; helper_argv[1] = passwd->pw_name; - helper_argv[2] = session->cookie; - helper_argv[3] = NULL; + helper_argv[2] = NULL; - session->child_stdin = -1; session->child_stdout = -1; error = NULL; @@ -615,7 +610,7 @@ polkit_agent_session_initiate (PolkitAgentSession *session) NULL, NULL, &session->child_pid, - &session->child_stdin, + &stdin_fd, &session->child_stdout, NULL, &error)) @@ -628,6 +623,13 @@ polkit_agent_session_initiate (PolkitAgentSession *session) if (G_UNLIKELY (_show_debug ())) g_print ("PolkitAgentSession: spawned helper with pid %d\n", (gint) session->child_pid); + session->child_stdin = (GOutputStream*)g_unix_output_stream_new (stdin_fd, TRUE); + + /* Write the cookie on stdin so it can't be seen by other processes */ + (void) g_output_stream_write_all (session->child_stdin, session->cookie, strlen (session->cookie), + NULL, NULL, NULL); + (void) g_output_stream_write_all (session->child_stdin, "\n", 1, NULL, NULL, NULL); + session->child_stdout_channel = g_io_channel_unix_new (session->child_stdout); session->child_stdout_watch_source = g_io_create_watch (session->child_stdout_channel, G_IO_IN | G_IO_ERR | G_IO_HUP); diff --git a/src/polkitbackend/polkitbackendinteractiveauthority.c b/src/polkitbackend/polkitbackendinteractiveauthority.c index dab2756..ee0e27b 100644 --- a/src/polkitbackend/polkitbackendinteractiveauthority.c +++ b/src/polkitbackend/polkitbackendinteractiveauthority.c @@ -214,6 +214,8 @@ typedef struct GDBusConnection *system_bus_connection; guint name_owner_changed_signal_id; + + guint64 agent_serial; } PolkitBackendInteractiveAuthorityPrivate; /* ---------------------------------------------------------------------------------------------------- */ @@ -431,11 +433,15 @@ struct AuthenticationAgent volatile gint ref_count; PolkitSubject *scope; + guint64 serial; gchar *locale; GVariant *registration_options; gchar *object_path; gchar *unique_system_bus_name; + GRand *cookie_pool; + gchar *cookie_prefix; + guint64 cookie_serial; GDBusProxy *proxy; @@ -1419,9 +1425,54 @@ authentication_session_cancelled_cb (GCancellable *cancellable, authentication_session_cancel (session); } +/* We're not calling this a UUID, but it's basically + * the same thing, just not formatted that way because: + * + * - I'm too lazy to do it + * - If we did, people might think it was actually + * generated from /dev/random, which we're not doing + * because this value doesn't actually need to be + * globally unique. + */ +static void +append_rand_u128_str (GString *buf, + GRand *pool) +{ + g_string_append_printf (buf, "%08x%08x%08x%08x", + g_rand_int (pool), + g_rand_int (pool), + g_rand_int (pool), + g_rand_int (pool)); +} + +/* A value that should be unique to the (AuthenticationAgent, AuthenticationSession) + * pair, and not guessable by other agents. + * + * - - - + * + * See http://lists.freedesktop.org/archives/polkit-devel/2015-June/000425.html + * + */ +static gchar * +authentication_agent_generate_cookie (AuthenticationAgent *agent) +{ + GString *buf = g_string_new (""); + + g_string_append (buf, agent->cookie_prefix); + + g_string_append_c (buf, '-'); + agent->cookie_serial++; + g_string_append_printf (buf, "%" G_GUINT64_FORMAT, + agent->cookie_serial); + g_string_append_c (buf, '-'); + append_rand_u128_str (buf, agent->cookie_pool); + + return g_string_free (buf, FALSE); +} + + static AuthenticationSession * authentication_session_new (AuthenticationAgent *agent, - const gchar *cookie, PolkitSubject *subject, PolkitIdentity *user_of_subject, PolkitSubject *caller, @@ -1439,7 +1490,7 @@ authentication_session_new (AuthenticationAgent *agent, session = g_new0 (AuthenticationSession, 1); session->agent = authentication_agent_ref (agent); - session->cookie = g_strdup (cookie); + session->cookie = authentication_agent_generate_cookie (agent); session->subject = g_object_ref (subject); session->user_of_subject = g_object_ref (user_of_subject); session->caller = g_object_ref (caller); @@ -1488,16 +1539,6 @@ authentication_session_free (AuthenticationSession *session) g_free (session); } -static gchar * -authentication_agent_new_cookie (AuthenticationAgent *agent) -{ - static gint counter = 0; - - /* TODO: use a more random-looking cookie */ - - return g_strdup_printf ("cookie%d", counter++); -} - static PolkitSubject * authentication_agent_get_scope (AuthenticationAgent *agent) { @@ -1545,12 +1586,15 @@ authentication_agent_unref (AuthenticationAgent *agent) g_free (agent->unique_system_bus_name); if (agent->registration_options != NULL) g_variant_unref (agent->registration_options); + g_rand_free (agent->cookie_pool); + g_free (agent->cookie_prefix); g_free (agent); } } static AuthenticationAgent * -authentication_agent_new (PolkitSubject *scope, +authentication_agent_new (guint64 serial, + PolkitSubject *scope, const gchar *unique_system_bus_name, const gchar *locale, const gchar *object_path, @@ -1584,6 +1628,7 @@ authentication_agent_new (PolkitSubject *scope, agent = g_new0 (AuthenticationAgent, 1); agent->ref_count = 1; + agent->serial = serial; agent->scope = g_object_ref (scope); agent->object_path = g_strdup (object_path); agent->unique_system_bus_name = g_strdup (unique_system_bus_name); @@ -1591,6 +1636,25 @@ authentication_agent_new (PolkitSubject *scope, agent->registration_options = registration_options != NULL ? g_variant_ref (registration_options) : NULL; agent->proxy = proxy; + { + GString *cookie_prefix = g_string_new (""); + GRand *agent_private_rand = g_rand_new (); + + g_string_append_printf (cookie_prefix, "%" G_GUINT64_FORMAT "-", agent->serial); + + /* Use a uniquely seeded PRNG to get a prefix cookie for this agent, + * whose sequence will not correlate with the per-authentication session + * cookies. + */ + append_rand_u128_str (cookie_prefix, agent_private_rand); + g_rand_free (agent_private_rand); + + agent->cookie_prefix = g_string_free (cookie_prefix, FALSE); + + /* And a newly seeded pool for per-session cookies */ + agent->cookie_pool = g_rand_new (); + } + return agent; } @@ -2185,7 +2249,6 @@ authentication_agent_initiate_challenge (AuthenticationAgent *agent, { PolkitBackendInteractiveAuthorityPrivate *priv = POLKIT_BACKEND_INTERACTIVE_AUTHORITY_GET_PRIVATE (authority); AuthenticationSession *session; - gchar *cookie; GList *l; GList *identities; gchar *localized_message; @@ -2207,8 +2270,6 @@ authentication_agent_initiate_challenge (AuthenticationAgent *agent, &localized_icon_name, &localized_details); - cookie = authentication_agent_new_cookie (agent); - identities = NULL; /* select admin user if required by the implicit authorization */ @@ -2271,7 +2332,6 @@ authentication_agent_initiate_challenge (AuthenticationAgent *agent, user_identities = g_list_prepend (NULL, polkit_unix_user_new (0)); session = authentication_session_new (agent, - cookie, subject, user_of_subject, caller, @@ -2327,7 +2387,6 @@ authentication_agent_initiate_challenge (AuthenticationAgent *agent, g_list_free_full (user_identities, g_object_unref); g_list_foreach (identities, (GFunc) g_object_unref, NULL); g_list_free (identities); - g_free (cookie); g_free (localized_message); g_free (localized_icon_name); @@ -2474,7 +2533,9 @@ polkit_backend_interactive_authority_register_authentication_agent (PolkitBacken goto out; } - agent = authentication_agent_new (subject, + priv->agent_serial++; + agent = authentication_agent_new (priv->agent_serial, + subject, polkit_system_bus_name_get_name (POLKIT_SYSTEM_BUS_NAME (caller)), locale, object_path, -- 2.4.2