perf/core: Fix use-after-free bug (a76a82a3) · Commits · 戴 / test

Dmitry reported a KASAN use-after-free on event->group_leader. It turns out there's a hole in perf_remove_from_context() due to event_function_call() not calling its function when the task associated with the event is already dead. In this case the event will have been detached from the task, but the grouping will have been retained, such that group operations might still work properly while there are live child events etc. This does however mean that we can miss a perf_group_detach() call when the group decomposes, this in turn can then lead to use-after-free. Fix it by explicitly doing the group detach if its still required. Reported-by:

Dmitry Vyukov <dvyukov@google.com> Tested-by:

Dmitry Vyukov <dvyukov@google.com> Signed-off-by:

Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com> Cc: Arnaldo Carvalho de Melo <acme@kernel.org> Cc: Arnaldo Carvalho de Melo <acme@redhat.com> Cc: Jiri Olsa <jolsa@redhat.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: stable@vger.kernel.org # v4.5+ Cc: syzkaller <syzkaller@googlegroups.com> Fixes: ("perf: Fix perf_event_exit_task() race") Link: http://lkml.kernel.org/r/20170126153955.GD6515@twins.programming.kicks-ass.net Signed-off-by:

Ingo Molnar <mingo@kernel.org>

kernel/events/core.c

+25 −2

Original line number	Diff line number	Diff line
		@@ -1469,7 +1469,6 @@ ctx_group_list(struct perf_event event, struct perf_event_context ctx)
		static void
		list_add_event(struct perf_event event, struct perf_event_context ctx)
		{

		lockdep_assert_held(&ctx->lock);

		WARN_ON_ONCE(event->attach_state & PERF_ATTACH_CONTEXT);
		@@ -1624,6 +1623,8 @@ static void perf_group_attach(struct perf_event *event)
		{
		struct perf_event group_leader = event->group_leader, pos;

		lockdep_assert_held(&event->ctx->lock);

		/*
		* We can have double attach due to group movement in perf_event_open.
		*/
		@@ -1697,6 +1698,8 @@ static void perf_group_detach(struct perf_event *event)
		struct perf_event sibling, tmp;
		struct list_head *list = NULL;

		lockdep_assert_held(&event->ctx->lock);

		/*
		* We can have double detach due to exit/hot-unplug + close.
		*/
		@@ -1895,9 +1898,29 @@ __perf_remove_from_context(struct perf_event *event,
		*/
		static void perf_remove_from_context(struct perf_event *event, unsigned long flags)
		{
		lockdep_assert_held(&event->ctx->mutex);
		struct perf_event_context *ctx = event->ctx;

		lockdep_assert_held(&ctx->mutex);

		event_function_call(event, __perf_remove_from_context, (void *)flags);

		/*
		* The above event_function_call() can NO-OP when it hits
		* TASK_TOMBSTONE. In that case we must already have been detached
		* from the context (by perf_event_exit_event()) but the grouping
		* might still be in-tact.
		*/
		WARN_ON_ONCE(event->attach_state & PERF_ATTACH_CONTEXT);
		if ((flags & DETACH_GROUP) &&
		(event->attach_state & PERF_ATTACH_GROUP)) {
		/*
		* Since in that case we cannot possibly be scheduled, simply
		* detach now.
		*/
		raw_spin_lock_irq(&ctx->lock);
		perf_group_detach(event);
		raw_spin_unlock_irq(&ctx->lock);
		}
		}

		/*

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