tracing: reset ring buffer when removing modules with events (9456f0fa) · Commits · 戴 / test

Li Zefan found that there's a race using the event ids of events and modules. When a module is loaded, an event id is incremented. We only have 16 bits for event ids (65536) and there is a possible (but highly unlikely) race that we could load and unload a module that registers events so many times that the event id counter overflows. When it overflows, it then restarts and goes looking for available ids. An id is available if it was added by a module and released. The race is if you have one module add an id, and then is removed. Another module loaded can use that same event id. But if the old module still had events in the ring buffer, the new module's call back would get bogus data. At best (and most likely) the output would just be garbage. But if the module for some reason used pointers (not recommended) then this could potentially crash. The safest thing to do is just reset the ring buffer if a module that registered events is removed. [ Impact: prevent unpredictable results of event id overflows ] Reported-by:

Li Zefan <lizf@cn.fujitsu.com> LKML-Reference: <49FEAFD0.30106@cn.fujitsu.com> Signed-off-by:

Steven Rostedt <rostedt@goodmis.org>

kernel/trace/trace.c

+10 −0

Original line number	Diff line number	Diff line
		@@ -639,6 +639,16 @@ void tracing_reset_online_cpus(struct trace_array *tr)
		tracing_reset(tr, cpu);
		}

		void tracing_reset_current(int cpu)
		{
		tracing_reset(&global_trace, cpu);
		}

		void tracing_reset_current_online_cpus(void)
		{
		tracing_reset_online_cpus(&global_trace);
		}

		#define SAVED_CMDLINES 128
		#define NO_CMDLINE_MAP UINT_MAX
		static unsigned map_pid_to_cmdline[PID_MAX_DEFAULT+1];

kernel/trace/trace.h

+2 −0

Original line number	Diff line number	Diff line
		@@ -409,6 +409,8 @@ int tracing_is_enabled(void);
		void trace_wake_up(void);
		void tracing_reset(struct trace_array *tr, int cpu);
		void tracing_reset_online_cpus(struct trace_array *tr);
		void tracing_reset_current(int cpu);
		void tracing_reset_current_online_cpus(void);
		int tracing_open_generic(struct inode inode, struct file filp);
		struct dentry trace_create_file(const char name,
		mode_t mode,

kernel/trace/trace_events.c

+9 −0

Original line number	Diff line number	Diff line
		@@ -932,9 +932,11 @@ static void trace_module_remove_events(struct module *mod)
		{
		struct ftrace_module_file_ops *file_ops;
		struct ftrace_event_call call, p;
		bool found = false;

		list_for_each_entry_safe(call, p, &ftrace_events, list) {
		if (call->mod == mod) {
		found = true;
		if (call->enabled) {
		call->enabled = 0;
		call->unregfunc();
		@@ -957,6 +959,13 @@ static void trace_module_remove_events(struct module *mod)
		list_del(&file_ops->list);
		kfree(file_ops);
		}

		/*
		* It is safest to reset the ring buffer if the module being unloaded
		* registered any events.
		*/
		if (found)
		tracing_reset_current_online_cpus();
		}

		static int trace_module_notify(struct notifier_block *self,

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