Messages in this thread | | | Subject | Re: [PATCH 1/2] coresight: tmc-etf: Fix NULL ptr dereference in tmc_enable_etf_sink_perf() | From | Suzuki K Poulose <> | Date | Tue, 13 Oct 2020 17:35:11 +0100 |
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On 10/07/2020 02:00 PM, Sai Prakash Ranjan wrote: > There was a report of NULL pointer dereference in ETF enable > path for perf CS mode with PID monitoring. It is almost 100% > reproducible when the process to monitor is something very > active such as chrome and with ETF as the sink and not ETR. > Currently in a bid to find the pid, the owner is dereferenced > via task_pid_nr() call in tmc_enable_etf_sink_perf() and with > owner being NULL, we get a NULL pointer dereference. > > Looking at the ETR and other places in the kernel, ETF and the > ETB are the only places trying to dereference the task(owner) > in tmc_enable_etf_sink_perf() which is also called from the > sched_in path as in the call trace. Owner(task) is NULL even > in the case of ETR in tmc_enable_etr_sink_perf(), but since we > cache the PID in alloc_buffer() callback and it is done as part > of etm_setup_aux() when allocating buffer for ETR sink, we never > dereference this NULL pointer and we are safe. So lets do the
The patch is necessary to fix some of the issues. But I feel it is not complete. Why is it safe earlier and not later ? I believe we are simply reducing the chances of hitting the issue, by doing this earlier than later. I would say we better fix all instances to make sure that the event->owner is valid. (e.g, I can see that the for kernel events event->owner == -1 ?)
struct task_struct *tsk = READ_ONCE(event->owner);
if (!tsk || is_kernel_event(event)) /* skip ? */
Suzuki
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