Re: perf: use-after-free in perf_release

From	Oleg Nesterov <oleg@redhat.com>
Newsgroups	linux.kernel
Subject	Re: perf: use-after-free in perf_release
Date	2017-03-14 14:30 +0100
Message-ID	<tkUGt-Hf-15@gated-at.bofh.it> (permalink)
References	(1 earlier) <ti0S5-lW-1@gated-at.bofh.it> <tinYm-6Q-23@gated-at.bofh.it> <tiohI-h2-23@gated-at.bofh.it> <tirfA-2oi-15@gated-at.bofh.it> <tkUds-cW-25@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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On 03/14, Peter Zijlstra wrote:
>
> On Tue, Mar 07, 2017 at 05:51:32PM +0100, Oleg Nesterov wrote:
>
> > inherit_event() returns NULL under is_orphaned_event() check, not ERR_PTR().
> > Is it correct?
>
> Yes. This is all a tad tricky, but it seems to be correct.
>
> By returning NULL, not an error, we affect the silent discard of
> orphaned events. This is correct, because otherwise
> perf_event_release_kernel() would have come by and explicitly discarded
> those events for us anyway.

Thanks... I'll try to understand this later.

> @@ -10608,7 +10627,6 @@ inherit_task_group(struct perf_event *event, struct task_struct *parent,
>  		 * First allocate and initialize a context for the
>  		 * child.
>  		 */
> -
>  		child_ctx = alloc_perf_context(parent_ctx->pmu, child);
>  		if (!child_ctx)
>  			return -ENOMEM;
> @@ -10670,7 +10688,7 @@ static int perf_event_init_context(struct task_struct *child, int ctxn)
>  		ret = inherit_task_group(event, parent, parent_ctx,
>  					 child, ctxn, &inherited_all);
>  		if (ret)
> -			break;
> +			goto out_unlock;
>  	}
>  
>  	/*
> @@ -10686,7 +10704,7 @@ static int perf_event_init_context(struct task_struct *child, int ctxn)
>  		ret = inherit_task_group(event, parent, parent_ctx,
>  					 child, ctxn, &inherited_all);
>  		if (ret)
> -			break;
> +			goto out_unlock;

With this change you can also simplify inherit_task_group() a little bit,
it no longer needs to nullify *inherited_all if inherit_group() fails.

Oleg.

Thread

perf: use-after-free in perf_release Dmitry Vyukov <dvyukov@google.com> - 2017-03-06 11:00 +0100
  Re: perf: use-after-free in perf_release Peter Zijlstra <peterz@infradead.org> - 2017-03-06 13:20 +0100
    Re: perf: use-after-free in perf_release Dmitry Vyukov <dvyukov@google.com> - 2017-03-06 13:20 +0100
      Re: perf: use-after-free in perf_release Peter Zijlstra <peterz@infradead.org> - 2017-03-06 13:30 +0100
        Re: perf: use-after-free in perf_release Dmitry Vyukov <dvyukov@google.com> - 2017-03-06 13:40 +0100
          Re: perf: use-after-free in perf_release Peter Zijlstra <peterz@infradead.org> - 2017-03-06 13:50 +0100
  Re: perf: use-after-free in perf_release Peter Zijlstra <peterz@infradead.org> - 2017-03-06 14:30 +0100
    Re: perf: use-after-free in perf_release Dmitry Vyukov <dvyukov@google.com> - 2017-03-06 14:40 +0100
      Re: perf: use-after-free in perf_release Dmitry Vyukov <dvyukov@google.com> - 2017-03-07 10:30 +0100
        Re: perf: use-after-free in perf_release Dmitry Vyukov <dvyukov@google.com> - 2017-03-07 10:50 +0100
          Re: perf: use-after-free in perf_release Peter Zijlstra <peterz@infradead.org> - 2017-03-07 12:50 +0100
        Re: perf: use-after-free in perf_release Peter Zijlstra <peterz@infradead.org> - 2017-03-07 11:40 +0100
      Re: perf: use-after-free in perf_release Peter Zijlstra <peterz@infradead.org> - 2017-03-07 10:50 +0100
    Re: perf: use-after-free in perf_release Peter Zijlstra <peterz@infradead.org> - 2017-03-07 14:20 +0100
      Re: perf: use-after-free in perf_release Peter Zijlstra <peterz@infradead.org> - 2017-03-07 15:10 +0100
    Re: perf: use-after-free in perf_release Oleg Nesterov <oleg@redhat.com> - 2017-03-07 15:10 +0100
      Re: perf: use-after-free in perf_release Dmitry Vyukov <dvyukov@google.com> - 2017-03-07 15:30 +0100
        Re: perf: use-after-free in perf_release Peter Zijlstra <peterz@infradead.org> - 2017-03-07 18:40 +0100
        Re: perf: use-after-free in perf_release Oleg Nesterov <oleg@redhat.com> - 2017-03-07 18:50 +0100
          Re: perf: use-after-free in perf_release Peter Zijlstra <peterz@infradead.org> - 2017-03-14 14:00 +0100
            Re: perf: use-after-free in perf_release Oleg Nesterov <oleg@redhat.com> - 2017-03-14 14:30 +0100
              Re: perf: use-after-free in perf_release Peter Zijlstra <peterz@infradead.org> - 2017-03-14 14:50 +0100
            Re: perf: use-after-free in perf_release Oleg Nesterov <oleg@redhat.com> - 2017-03-14 15:10 +0100
              Re: perf: use-after-free in perf_release Peter Zijlstra <peterz@infradead.org> - 2017-03-14 15:10 +0100
                Re: perf: use-after-free in perf_release Oleg Nesterov <oleg@redhat.com> - 2017-03-14 15:40 +0100
                Re: perf: use-after-free in perf_release Peter Zijlstra <peterz@infradead.org> - 2017-03-14 16:10 +0100
                Re: perf: use-after-free in perf_release Peter Zijlstra <peterz@infradead.org> - 2017-03-14 16:10 +0100
                Re: perf: use-after-free in perf_release Oleg Nesterov <oleg@redhat.com> - 2017-03-14 16:40 +0100
                Re: perf: use-after-free in perf_release Peter Zijlstra <peterz@infradead.org> - 2017-03-14 16:50 +0100
                Re: perf: use-after-free in perf_release Peter Zijlstra <peterz@infradead.org> - 2017-03-14 16:30 +0100
                Re: perf: use-after-free in perf_release Peter Zijlstra <peterz@infradead.org> - 2017-03-14 18:40 +0100
                Re: perf: use-after-free in perf_release Oleg Nesterov <oleg@redhat.com> - 2017-03-15 17:50 +0100
                Re: perf: use-after-free in perf_release Peter Zijlstra <peterz@infradead.org> - 2017-03-16 13:10 +0100
                Re: perf: use-after-free in perf_release Peter Zijlstra <peterz@infradead.org> - 2017-03-16 15:00 +0100
                Re: perf: use-after-free in perf_release Oleg Nesterov <oleg@redhat.com> - 2017-03-16 17:50 +0100
                Re: perf: use-after-free in perf_release Oleg Nesterov <oleg@redhat.com> - 2017-03-14 16:30 +0100

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