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Date: Thu, 28 May 2009 04:54:07 +0200 From: Oleg Nesterov <oleg@...hat.com> To: Roland McGrath <roland@...hat.com> Cc: Christoph Hellwig <hch@...radead.org>, Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org Subject: Re: [RFC PATCH 7/X] ptrace: mv task->parent ptrace_task->pt_tracer 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@...hat.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. */ -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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