Re: [PATCH ? 2/2] setpgid: should work for sub-threads

[Oren Laadan <orenl@cs.columbia.edu>]

[PATCH 1/1] setsid: 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>

---

(see similar patch for setpgid by Oleg Nesterov). This one also required 
modifying kernel/exit.c:__set_special_pids() (and it's prototype in 
sched.h).

Please review...

diff --git a/include/linux/sched.h b/include/linux/sched.h
index b0ad6f3..9ff6e79 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1003,7 +1003,7 @@ extern struct   mm_struct init_mm;
 #define find_task_by_pid(nr)	find_task_by_pid_type(PIDTYPE_PID, nr)
 extern struct task_struct *find_task_by_pid_type(int type, int pid);
 extern void set_special_pids(pid_t session, pid_t pgrp);
-extern void __set_special_pids(pid_t session, pid_t pgrp);
+extern void __set_special_pids(struct task_struct *tsk, pid_t session, pid_t pgrp);

 /* per-UID process charging. */
 extern struct user_struct * alloc_uid(uid_t);
diff --git a/kernel/exit.c b/kernel/exit.c
index ee51568..d47931f 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -256,26 +256,24 @@ static inline void reparent_to_init(void
 	switch_uid(INIT_USER);
 }

-void __set_special_pids(pid_t session, pid_t pgrp)
+void __set_special_pids(struct task_struct *tsk, pid_t session, pid_t pgrp)
 {
-	struct task_struct *curr = current;
-
-	if (curr->signal->session != session) {
-		detach_pid(curr, PIDTYPE_SID);
-		curr->signal->session = session;
-		attach_pid(curr, PIDTYPE_SID, session);
-	}
-	if (process_group(curr) != pgrp) {
-		detach_pid(curr, PIDTYPE_PGID);
-		curr->signal->pgrp = pgrp;
-		attach_pid(curr, PIDTYPE_PGID, pgrp);
+	if (tsk->signal->session != session) {
+		detach_pid(tsk, PIDTYPE_SID);
+		tsk->signal->session = session;
+		attach_pid(tsk, PIDTYPE_SID, session);
+	}
+	if (process_group(tsk) != pgrp) {
+		detach_pid(tsk, PIDTYPE_PGID);
+		tsk->signal->pgrp = pgrp;
+		attach_pid(tsk, PIDTYPE_PGID, pgrp);
 	}
 }

 void set_special_pids(pid_t session, pid_t pgrp)
 {
 	write_lock_irq(&tasklist_lock);
-	__set_special_pids(session, pgrp);
+	__set_special_pids(current, session, pgrp);
 	write_unlock_irq(&tasklist_lock);
 }

diff --git a/kernel/sys.c b/kernel/sys.c
index bce933e..c907f88 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -1207,24 +1207,22 @@ asmlinkage long sys_getsid(pid_t pid)

 asmlinkage long sys_setsid(void)
 {
+	struct task_struct *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, 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);
+	leader->signal->leader = 1;
+	__set_special_pids(leader, leader->pid, leader->pid);
+	leader->signal->tty = NULL;
+	leader->signal->tty_old_pgrp = 0;
+	err = process_group(leader);
 out:
 	write_unlock_irq(&tasklist_lock);
 	up(&tty_sem);



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