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login: fix user@.service case, so we don't allow nested sessions (#8051)

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> logind sessions are mostly bound to the audit session concept, and audit
> sessions remain unaffected by "su", in fact they are defined to be
> "sealed off", i.e. in a way that if a process entered a session once, it
> will always stay with it, and so will its children, i.e. the only way to
> get a new session is by forking off something off PID 1 (or something
> similar) that never has been part of a session.

The code had a gap.  user@.service is a special case PAM session which does
not create a logind session.  Let's remember to check for it.

Fixes #8021
This commit is contained in:
Alan Jenkins 2018-02-22 20:38:44 +00:00 committed by Zbigniew Jędrzejewski-Szmek
parent 5547c12503
commit e8a3144ec4
1 changed files with 11 additions and 2 deletions
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13
src/login/logind-dbus.c
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@ -41,6 +41,7 @@
#include "mkdir.h"
#include "path-util.h"
#include "process-util.h"
#include "cgroup-util.h"
#include "selinux-util.h"
#include "sleep-config.h"
#include "special.h"
@ -658,6 +659,7 @@ static int method_list_inhibitors(sd_bus_message *message, void *userdata, sd_bu
static int method_create_session(sd_bus_message *message, void *userdata, sd_bus_error *error) {
const char *service, *type, *class, *cseat, *tty, *display, *remote_user, *remote_host, *desktop;
uint32_t audit_id = 0;
_cleanup_free_ char *unit = NULL;
_cleanup_free_ char *id = NULL;
Session *session = NULL;
Manager *m = userdata;
@ -787,8 +789,15 @@ static int method_create_session(sd_bus_message *message, void *userdata, sd_bus
return r;
}
r = manager_get_session_by_pid(m, leader, NULL);
if (r > 0)
/*
* Check if we are already in a logind session. Or if we are in user@.service
* which is a special PAM session that avoids creating a logind session.
*/
r = cg_pid_get_unit(leader, &unit);
if (r < 0)
return r;
if (hashmap_get(m->session_units, unit) ||
hashmap_get(m->user_units, unit))
return sd_bus_error_setf(error, BUS_ERROR_SESSION_BUSY, "Already running in a session");
/*