fix setsid() for sub-namespace /sbin/init

sys_setsid() still deals with pid_t's from the global namespace. This means
that the "session > 1" check can't help for sub-namespace init, setsid() can't
succeed because copy_process(CLONE_NEWPID) populates PIDTYPE_PGID/SID links.

Remove the usage of task_struct->pid and convert the code to use "struct pid".
This also simplifies and speedups the code, saves one find_pid().

Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Acked-by: Pavel Emelyanov <xemul@openvz.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 10 insertions, 12 deletions

diff --git a/kernel/sys.c b/kernel/sys.c
index 42136dd453d1..e13bc518b444 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -1045,35 +1045,33 @@ asmlinkage long sys_getsid(pid_t pid)
 asmlinkage long sys_setsid(void)
 {
         struct task_struct *group_leader = current->group_leader;
-        pid_t session;
+        struct pid *sid = task_pid(group_leader);
+        pid_t session = pid_vnr(sid);
         int err = -EPERM;
 
         write_lock_irq(&tasklist_lock);
-
         /* Fail if I am already a session leader */
         if (group_leader->signal->leader)
                 goto out;
 
-        session = group_leader->pid;
-        /* Fail if a process group id already exists that equals the
-         * proposed session id.
+        /* Fail if a process group id already exists that equals the proposed
+         * session id.
          *
-         * Don't check if session id == 1 because kernel threads use this
-         * session id and so the check will always fail and make it so
-         * init cannot successfully call setsid.
+         * Don't check if session == 1 because kernel threads and CLONE_NEWPID
+         * tasks use this session id and so the check will always fail and make
+         * it so init cannot successfully call setsid.
          */
-        if (session > 1 && find_task_by_pid_type_ns(PIDTYPE_PGID,
-                                session, &init_pid_ns))
+        if (session != 1 && pid_task(sid, PIDTYPE_PGID))
                 goto out;
 
         group_leader->signal->leader = 1;
-        __set_special_pids(session, session);
+        __set_special_pids(pid_nr(sid), pid_nr(sid));
 
         spin_lock(&group_leader->sighand->siglock);
         group_leader->signal->tty = NULL;
         spin_unlock(&group_leader->sighand->siglock);
 
-        err = task_pgrp_vnr(group_leader);
+        err = session;
 out:
         write_unlock_irq(&tasklist_lock);
         return err;