Messages in this thread | | | Date | Mon, 8 Nov 2010 19:41:00 +0100 | From | Frederic Weisbecker <> | Subject | Re: Q: perf_event && task->ptrace_bps[] |
| |
On Mon, Nov 08, 2010 at 03:56:47PM +0100, Oleg Nesterov wrote: > Hello. > > I am trying to understand the usage of hw-breakpoints in arch_ptrace(). > ptrace_set_debugreg() and related code looks obviously racy. Nothing > protects us against flush_ptrace_hw_breakpoint() called by the dying > tracee. Afaics we can leak perf_event or use the already freed memory > or both. > > Am I missed something? > > Looking into the git history, I don't even know which patch should be > blamed (if I am right), there were too many changes. I noticed that > 2ebd4ffb6d0cb877787b1e42be8485820158857e "perf events: Split out task > search into helper" moved the PF_EXITING check from find_get_context(). > This check coould help if sys_ptrace() races with SIGKILL, but it was > racy anyway. > > It is not clear to me what should be done. Looking more, I do not > understand the scope of perf_event/ctx at all, sys_perf_event_open() > looks wrong too, see the next email I am going to send. > > Oleg. >
But I don't understand how ptrace_set_debugreg() and flush_old_exec() can happen at the same time. The parent can only do the ptrace request when the child is stopped, right? But it can't be stopped in flush_old_exec()...?
Not sure how any race can happen here. I am certainly missing something obvious.
Thanks.
| |