(2013/07/05 9:32), Oleg Nesterov wrote: > On 07/04, Masami Hiramatsu wrote: >> >> Currently ftrace_open_generic_file gets an event_file from >> inode->i_private, and then locks event_mutex and gets refcount. >> However, this can cause a race as below scenario; >> >> CPU0 CPU1 >> open(kprobe_events) >> trace_remove_event_call() open(enable) >> lock event_mutex get event_file from inode->i_private >> event_remove() wait for unlock event_mutex >> ... >> free event_file >> unlock event_mutex >> lock event_mutex >> add refcount of event_file->call (*) >> >> So, at (*) point, the event_file is already freed and we >> may access the corrupted object. > > Yes, but the same can happen with event_call, so it seems that > this patch is not enough too.
Oops, right! > Say, open(id) can take event_mutex when the caller of > trace_remove_event_call() has already freed ftrace_event_call. > > Or I missed something... > > Perhaps we can rely on d_unlinked() ? IOW, the caller of > __ftrace_event_call_get() should take event_mutex, check > d_unhashed(f_dentry) and only then do _get(). It sounds a good idea! :) Thank you! > > Nasty, I agree. > > Oleg. > > -- Masami HIRAMATSU IT Management Research Dept. Linux Technology Center Hitachi, Ltd., Yokohama Research Laboratory E-mail: [email protected] -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
