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pam: cache sd-bus separately per module

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sd-bus connection is cached by the two pam modules globally, but this
can lead to issues due to hashmaps (used by sd-bus) using a global
static variable for the shared hash key, which is different per module
as both modules are loaded in the same process.

This happens because the sd-bus object is create in one module, but
used in the other, so global state does not match.

Use a different pam cache identifier for the sd-bus pointer, so that
each module uses a different sd-bus connection as a workaround.

Fixes https://github.com/systemd/systemd/issues/27216
Fixes https://github.com/systemd/systemd/issues/17266
This commit is contained in:
Luca Boccassi 2023-04-16 14:55:09 +01:00 committed by Lennart Poettering
parent db0c0f5e00
commit a2dd39b4cb
4 changed files with 30 additions and 15 deletions
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10
src/home/pam_systemd_home.c
View file

@ -140,7 +140,7 @@ static int acquire_user_record(
_cleanup_(sd_bus_error_free) sd_bus_error error = SD_BUS_ERROR_NULL;
_cleanup_free_ char *generic_field = NULL, *json_copy = NULL;
r = pam_acquire_bus_connection(handle, &bus);
r = pam_acquire_bus_connection(handle, "pam-systemd-home", &bus);
if (r != PAM_SUCCESS)
return r;
@ -513,7 +513,7 @@ static int acquire_home(
if (r == PAM_SUCCESS && PTR_TO_FD(home_fd_ptr) >= 0)
return PAM_SUCCESS;
r = pam_acquire_bus_connection(handle, &bus);
r = pam_acquire_bus_connection(handle, "pam-systemd-home", &bus);
if (r != PAM_SUCCESS)
return r;
@ -745,7 +745,7 @@ success:
/* Let's release the D-Bus connection, after all the session might live quite a long time, and we are
* not going to process the bus connection in that time, so let's better close before the daemon
* kicks us off because we are not processing anything. */
(void) pam_release_bus_connection(handle);
(void) pam_release_bus_connection(handle, "pam-systemd-home");
return PAM_SUCCESS;
}
@ -785,7 +785,7 @@ _public_ PAM_EXTERN int pam_sm_close_session(
if (r != PAM_SUCCESS)
return r;
r = pam_acquire_bus_connection(handle, &bus);
r = pam_acquire_bus_connection(handle, "pam-systemd-home", &bus);
if (r != PAM_SUCCESS)
return r;
@ -944,7 +944,7 @@ _public_ PAM_EXTERN int pam_sm_chauthtok(
if (debug)
pam_syslog(handle, LOG_DEBUG, "pam-systemd-homed account management");
r = pam_acquire_bus_connection(handle, &bus);
r = pam_acquire_bus_connection(handle, "pam-systemd-home", &bus);
if (r != PAM_SUCCESS)
return r;

6
src/login/pam_systemd.c
View file

@ -948,7 +948,7 @@ _public_ PAM_EXTERN int pam_sm_open_session(
/* Talk to logind over the message bus */
r = pam_acquire_bus_connection(handle, &bus);
r = pam_acquire_bus_connection(handle, "pam-systemd", &bus);
if (r != PAM_SUCCESS)
return r;
@ -1115,7 +1115,7 @@ success:
/* Let's release the D-Bus connection, after all the session might live quite a long time, and we are
* not going to use the bus connection in that time, so let's better close before the daemon kicks us
* off because we are not processing anything. */
(void) pam_release_bus_connection(handle);
(void) pam_release_bus_connection(handle, "pam-systemd");
return PAM_SUCCESS;
}
@ -1159,7 +1159,7 @@ _public_ PAM_EXTERN int pam_sm_close_session(
/* Before we go and close the FIFO we need to tell logind that this is a clean session
* shutdown, so that it doesn't just go and slaughter us immediately after closing the fd */
r = pam_acquire_bus_connection(handle, &bus);
r = pam_acquire_bus_connection(handle, "pam-systemd", &bus);
if (r != PAM_SUCCESS)
return r;

23
src/shared/pam-util.c
View file

@ -53,15 +53,21 @@ static void cleanup_system_bus(pam_handle_t *handle, void *data, int error_statu
sd_bus_flush_close_unref(data);
}
int pam_acquire_bus_connection(pam_handle_t *handle, sd_bus **ret) {
int pam_acquire_bus_connection(pam_handle_t *handle, const char *module_name, sd_bus **ret) {
_cleanup_(sd_bus_unrefp) sd_bus *bus = NULL;
_cleanup_free_ char *cache_id = NULL;
int r;
assert(handle);
assert(module_name);
assert(ret);
cache_id = strjoin("system-bus-", module_name);
if (!cache_id)
return pam_log_oom(handle);
/* We cache the bus connection so that we can share it between the session and the authentication hooks */
r = pam_get_data(handle, "systemd-system-bus", (const void**) &bus);
r = pam_get_data(handle, cache_id, (const void**) &bus);
if (r == PAM_SUCCESS && bus) {
*ret = sd_bus_ref(TAKE_PTR(bus)); /* Increase the reference counter, so that the PAM data stays valid */
return PAM_SUCCESS;
@ -73,7 +79,7 @@ int pam_acquire_bus_connection(pam_handle_t *handle, sd_bus **ret) {
if (r < 0)
return pam_syslog_errno(handle, LOG_ERR, r, "Failed to connect to system bus: %m");
r = pam_set_data(handle, "systemd-system-bus", bus, cleanup_system_bus);
r = pam_set_data(handle, cache_id, bus, cleanup_system_bus);
if (r != PAM_SUCCESS)
return pam_syslog_pam_error(handle, LOG_ERR, r, "Failed to set PAM bus data: @PAMERR@");
@ -83,10 +89,17 @@ int pam_acquire_bus_connection(pam_handle_t *handle, sd_bus **ret) {
return PAM_SUCCESS;
}
int pam_release_bus_connection(pam_handle_t *handle) {
int pam_release_bus_connection(pam_handle_t *handle, const char *module_name) {
_cleanup_free_ char *cache_id = NULL;
int r;
r = pam_set_data(handle, "systemd-system-bus", NULL, NULL);
assert(module_name);
cache_id = strjoin("system-bus-", module_name);
if (!cache_id)
return pam_log_oom(handle);
r = pam_set_data(handle, cache_id, NULL, NULL);
if (r != PAM_SUCCESS)
return pam_syslog_pam_error(handle, LOG_ERR, r, "Failed to release PAM user record data: @PAMERR@");

6
src/shared/pam-util.h
View file

@ -24,7 +24,9 @@ static inline int pam_bus_log_parse_error(pam_handle_t *handle, int r) {
return pam_syslog_errno(handle, LOG_ERR, r, "Failed to parse bus message: %m");
}
int pam_acquire_bus_connection(pam_handle_t *handle, sd_bus **ret);
int pam_release_bus_connection(pam_handle_t *handle);
/* Use a different module name per different PAM module. They are all loaded in the same namespace, and this
* helps avoid a clash in the internal data structures of sd-bus. It will be used as key for cache items. */
int pam_acquire_bus_connection(pam_handle_t *handle, const char *module_name, sd_bus **ret);
int pam_release_bus_connection(pam_handle_t *handle, const char *module_name);
void pam_cleanup_free(pam_handle_t *handle, void *data, int error_status);