Messages in this thread | | | Subject | Re: yama: unsafe usage of ptrace_relation->tracer | From | Tetsuo Handa <> | Date | Thu, 10 Jan 2019 20:05:47 +0900 |
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Hello, Kees.
syzbot is hitting this problem as of linux-next-20190110. When a patch will be proposed?
On 2018/10/30 0:05, Oleg Nesterov wrote: > let me change the subject to avoid the confusion with the already confusing > disccussion about task_is_descendant(). > > On 10/29, Oleg Nesterov wrote: >> >> I still think we need a single pid_alive() check and I even sent the patch. >> Attached again at the end. >> >> To clarify, let me repeat that ptracer_exception_found() may need some fixes >> too, right now I am only talking about task_is_descendant(). > > so yes, the ptracer_relations code looks very broken to me, but perhaps I > misread this code, please correct me. > > RCU can only protect the ptracer_relations list itself, you can do nothing > with (say) relation->tracer. relation->tracer can be already freed when > ptracer_exception_found() checks relation->tracee == tracee. > > Not only pid_alive(parent) can not help in this case, pid_alive(parent) is > equally unsafe because, again, this memory can be freed. > > security_task_free(tsk) is called right before free_task(tsk), there is no > a gp pass in between, and of course we can't rely on the ->invalid check. > > _At first glance_ we can fix this if we simply turn both ->tracer/tracee > pointers into "signal_struct *", then we can turn all same_thread_group()'s > into walker->signal == parent which doesn't need to dereference the possibly- > freed parent. This also allows to remove all thread_group_leader() checks. > We need to ensure that false-positive is not possible (if, say, ->tracer > was already re-allocated and points to another task->signal), but this > doesn't look difficult. > > Oleg. > >
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