Messages in this thread Patch in this message | | | Date | Thu, 28 May 2009 04:54:07 +0200 | From | Oleg Nesterov <> | Subject | Re: [RFC PATCH 7/X] ptrace: mv task->parent ptrace_task->pt_tracer |
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On 05/27, Roland McGrath wrote: > > > OK, lets do this change later ;) > > Agreed.
Damn. OTOH, it is so ugly to cache pid/uid for the very unlikely case.
Roland, will you agree with the patch below?
If yes, I'd like to send it separately.
Oleg.
------------------------------------------------------------------- [PATCH -mm] ptrace: ptrace_signal: fix the usage of ->parent
This patch complicates the code to fix the pure theoretical problems. But since we are going to change this code, it is better to fix them anyway.
- If we are not traced any longer after ptrace_stop(), si_pid/si_uid are not necessary right.
- It is not safe to dereference current->parent without tasklist or RCU lock. The tracer can detach and exit. ->siglock can't prevent this, and (in theory) local_irq_disable() doesn't imply RCU lock.
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
--- PTRACE/kernel/signal.c~PTRACE_SIGNAL 2009-05-28 04:12:02.000000000 +0200 +++ PTRACE/kernel/signal.c 2009-05-28 04:14:38.000000000 +0200 @@ -1770,11 +1770,22 @@ static int ptrace_signal(int signr, sigi specific in the siginfo structure then it should have updated *info via PTRACE_SETSIGINFO. */ if (signr != info->si_signo) { + struct task_struct *tracer; + info->si_signo = signr; info->si_errno = 0; info->si_code = SI_USER; - info->si_pid = task_pid_vnr(current->parent); - info->si_uid = task_uid(current->parent); + + rcu_read_lock(); + tracer = current->parent; + if (task_ptrace(current)) { + info->si_pid = task_pid_vnr(tracer); + info->si_uid = task_uid(tracer); + } else { + info->si_pid = 0; + info->si_uid = 0; + } + rcu_read_unlock(); } /* If the (new) signal is now blocked, requeue it. */
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