1 files changed, 15 insertions, 4 deletions

diff --git a/kernel/sys.c b/kernel/sys.c
index 7ef7f6054c28..0b6ec0e7936f 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -1372,18 +1372,29 @@ asmlinkage long sys_getsid(pid_t pid)
 asmlinkage long sys_setsid(void)
 {
         struct task_struct *group_leader = current->group_leader;
-        struct pid *pid;
+        pid_t session;
         int err = -EPERM;
 
         mutex_lock(&tty_mutex);
         write_lock_irq(&tasklist_lock);
 
-        pid = find_pid(PIDTYPE_PGID, group_leader->pid);
-        if (pid)
+        /* 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.
+         *
+         * 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.
+         */
+        if (session > 1 && find_task_by_pid_type(PIDTYPE_PGID, session))
                 goto out;
 
         group_leader->signal->leader = 1;
-        __set_special_pids(group_leader->pid, group_leader->pid);
+        __set_special_pids(session, session);
         group_leader->signal->tty = NULL;
         group_leader->signal->tty_old_pgrp = 0;
         err = process_group(group_leader);