2008-03-26 20:19:54

by Oleg Nesterov

[permalink] [raw]
Subject: [PATCH] ptrace: allow to ptrace /sbin/init

Afaics, currently there are no kernel problems with ptracing init, it can't
lose SIGNAL_UNKILLABLE flag and be killed/stopped by accident.

The ability to strace/debug init can be very useful if you try to figure
out why it does not work as expected.

However, admin should know what he does, "gdb /sbin/init 1" stops init, it
can't reap orphaned zombies or take care of /etc/inittab until continued.
It is even possible to crash init (and thus the whole system) if you wish,
ptracer has full control.

See also the long discussion: http://marc.info/?t=120628018600001

Signed-off-by: Oleg Nesterov <[email protected]>

--- 25/kernel/ptrace.c~INIT_PTRACEABLE 2008-03-26 21:31:39.000000000 +0300
+++ 25/kernel/ptrace.c 2008-03-26 21:33:35.000000000 +0300
@@ -168,8 +168,6 @@ int ptrace_attach(struct task_struct *ta
audit_ptrace(task);

retval = -EPERM;
- if (task->pid <= 1)
- goto out;
if (same_thread_group(task, current))
goto out;

@@ -517,12 +515,6 @@ struct task_struct *ptrace_get_task_stru
{
struct task_struct *child;

- /*
- * Tracing init is not allowed.
- */
- if (pid == 1)
- return ERR_PTR(-EPERM);
-
read_lock(&tasklist_lock);
child = find_task_by_vpid(pid);
if (child)


2008-03-26 20:41:06

by Roland McGrath

[permalink] [raw]
Subject: Re: [PATCH] ptrace: allow to ptrace /sbin/init

Fine by me!

Acked-by: Roland McGrath <[email protected]>


Thanks,
Roland

2008-03-27 07:24:15

by Pavel Emelyanov

[permalink] [raw]
Subject: Re: [PATCH] ptrace: allow to ptrace /sbin/init

Oleg Nesterov wrote:
> Afaics, currently there are no kernel problems with ptracing init, it can't
> lose SIGNAL_UNKILLABLE flag and be killed/stopped by accident.
>
> The ability to strace/debug init can be very useful if you try to figure
> out why it does not work as expected.
>
> However, admin should know what he does, "gdb /sbin/init 1" stops init, it
> can't reap orphaned zombies or take care of /etc/inittab until continued.
> It is even possible to crash init (and thus the whole system) if you wish,
> ptracer has full control.
>
> See also the long discussion: http://marc.info/?t=120628018600001
>
> Signed-off-by: Oleg Nesterov <[email protected]>

Acked-by: Pavel Emelyanov <[email protected]>