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PAM: Warn about issue with systemd-user service #13025

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PAM: Warn about issue with systemd-user service #13025

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30 changes: 30 additions & 0 deletions contrib/pam_zfs_key/pam_zfs_key.c
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Original file line number Diff line number Diff line change
Expand Up @@ -635,6 +635,35 @@ zfs_key_config_modify_session_counter(pam_handle_t *pamh,
return (counter_value);
}

/*
* This module only works if every opened session is later closed. There are
* known and common service(s) which violate this norm; warn if they are
* detected.
*
* Specifically, these <services> include "systemd-user".
*
* Workaround:
* session [success=1 default=ignore] pam_succeed_if.so service in <services>
* session optional pam_zfs_key.so
*/
static int
session_roundtrip_check(pam_handle_t *pamh)
{
const char *service;
int ret = pam_get_item(pamh, PAM_SERVICE, (const void **)&service);
if (ret != PAM_SUCCESS) {
pam_syslog(pamh, LOG_NOTICE, "Unable to identify PAM service");
return (-1);
}
if (strcmp("systemd-user", service) == 0) {
pam_syslog(pamh, LOG_WARNING,
"Key may not be unloaded because of "
"https://github.com/systemd/systemd/issues/8598");
return (1);
}
return (0);
}

__attribute__((visibility("default")))
PAM_EXTERN int
pam_sm_authenticate(pam_handle_t *pamh, int flags,
Expand Down Expand Up @@ -749,6 +778,7 @@ pam_sm_open_session(pam_handle_t *pamh, int flags,
"Cannot zfs_mount when not being root.");
return (PAM_SUCCESS);
}
(void) session_roundtrip_check(pamh);
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@nabijaczleweli nabijaczleweli Mar 8, 2022 •
edited
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What's the point of returning a tristate if the only user just void-casts it? The documentation says warn, and it just warns, so why not just warn?

static void
session_roundtrip_warn(pam_handle_t *pamh)
{
	const char *service;
	if (pam_get_item(pamh, PAM_SERVICE, (const void **)&service)
	    != PAM_SUCCESS)
		pam_syslog(pamh, LOG_NOTICE, "Unable to identify PAM service");
	else if (strcmp("systemd-user", service) == 0)
		pam_syslog(pamh, LOG_WARNING,
		    "Key may not be unloaded because of "
		    "https://github.com/systemd/systemd/issues/8598");
}

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I hoped to build on this change and add functionality based around the return value. However, I think those changes could generate a more vibrant discussion. Since this function provides value even in isolation, I decided to submit it separately.

Regardless, it doesn't seem to matter; both forms compile to the same binary on my system.

zfs_key_config_t config;
zfs_key_config_load(pamh, &config, argc, argv);
if (config.uid < 1000) {
Expand Down