From 390e2ff07712468ce6600a43aa91e897b056ce12 Mon Sep 17 00:00:00 2001 From: "Eric W. Biederman" Date: Fri, 31 Mar 2006 02:31:33 -0800 Subject: [PATCH] [PATCH] Make setsid() more robust The core problem: setsid fails if it is called by init. The effect in 2.6.16 and the earlier kernels that have this problem is that if you do a "ps -j 1 or ps -ej 1" you will see that init and several of it's children have process group and session == 0. Instead of process group == session == 1. Despite init calling setsid. The reason it fails is that daemonize calls set_special_pids(1,1) on kernel threads that are launched before /sbin/init is called. The only remaining effect in that current->signal->leader == 0 for init instead of 1. And the setsid call fails. No one has noticed because /sbin/init does not check the return value of setsid. In 2.4 where we don't have the pidhash table, and daemonize doesn't exist setsid actually works for init. I care a lot about pid == 1 not being a special case that we leave broken, because of the container/jail work that I am doing. - Carefully allow init (pid == 1) to call setsid despite the kernel using its session. - Use find_task_by_pid instead of find_pid because find_pid taking a pidtype is going away. Signed-off-by: Eric W. Biederman Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- kernel/sys.c | 19 +++++++++++++++---- 1 file changed, 15 insertions(+), 4 deletions(-) diff --git a/kernel/sys.c b/kernel/sys.c index 7ef7f6054c..0b6ec0e793 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); -- 2.39.5