[PATCH] setpgid: should work for sub-threads

setsid() does not work unless the calling process is a
thread_group_leader().

'man setpgid' does not tell anything about that, so I consider this
behaviour is a bug.

Signed-off-by: Oren Laadan <orenl@cs.columbia.edu>
Cc: Oleg Nesterov <oleg@tv-sign.ru>
Cc: Roland McGrath <roland@redhat.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

2 files changed, 8 insertions, 10 deletions

diff --git a/kernel/exit.c b/kernel/exit.c
index a80824f6108b..caceabf3f230 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -257,7 +257,7 @@ static inline void reparent_to_init(void)
 
 void __set_special_pids(pid_t session, pid_t pgrp)
 {
-        struct task_struct *curr = current;
+        struct task_struct *curr = current->group_leader;
 
         if (curr->signal->session != session) {
                 detach_pid(curr, PIDTYPE_SID);
diff --git a/kernel/sys.c b/kernel/sys.c
index 43e557211d8d..f497bf56ada1 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -1215,24 +1215,22 @@ asmlinkage long sys_getsid(pid_t pid)
 
 asmlinkage long sys_setsid(void)
 {
+        struct task_struct *group_leader = current->group_leader;
         struct pid *pid;
         int err = -EPERM;
 
-        if (!thread_group_leader(current))
-                return -EINVAL;
-
         down(&tty_sem);
         write_lock_irq(&tasklist_lock);
 
-        pid = find_pid(PIDTYPE_PGID, current->pid);
+        pid = find_pid(PIDTYPE_PGID, group_leader->pid);
         if (pid)
                 goto out;
 
-        current->signal->leader = 1;
-        __set_special_pids(current->pid, current->pid);
-        current->signal->tty = NULL;
-        current->signal->tty_old_pgrp = 0;
-        err = process_group(current);
+        group_leader->signal->leader = 1;
+        __set_special_pids(group_leader->pid, group_leader->pid);
+        group_leader->signal->tty = NULL;
+        group_leader->signal->tty_old_pgrp = 0;
+        err = process_group(group_leader);
 out:
         write_unlock_irq(&tasklist_lock);
         up(&tty_sem);