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    Subject[PATCH 3.18 071/124] perf/core: Fix event inheritance on fork()
    Date
    3.18-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Peter Zijlstra <peterz@infradead.org>

    commit e7cc4865f0f31698ef2f7aac01a50e78968985b7 upstream.

    While hunting for clues to a use-after-free, Oleg spotted that
    perf_event_init_context() can loose an error value with the result
    that fork() can succeed even though we did not fully inherit the perf
    event context.

    Spotted-by: Oleg Nesterov <oleg@redhat.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: Dmitry Vyukov <dvyukov@google.com>
    Cc: Frederic Weisbecker <fweisbec@gmail.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: Stephane Eranian <eranian@google.com>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    Cc: Vince Weaver <vincent.weaver@maine.edu>
    Cc: oleg@redhat.com
    Fixes: 889ff0150661 ("perf/core: Split context's event group list into pinned and non-pinned lists")
    Link: http://lkml.kernel.org/r/20170316125823.190342547@infradead.org
    Signed-off-by: Ingo Molnar <mingo@kernel.org>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    kernel/events/core.c | 5 +++--
    1 file changed, 3 insertions(+), 2 deletions(-)

    --- a/kernel/events/core.c
    +++ b/kernel/events/core.c
    @@ -8058,7 +8058,7 @@ static int perf_event_init_context(struc
    ret = inherit_task_group(event, parent, parent_ctx,
    child, ctxn, &inherited_all);
    if (ret)
    - break;
    + goto out_unlock;
    }

    /*
    @@ -8074,7 +8074,7 @@ static int perf_event_init_context(struc
    ret = inherit_task_group(event, parent, parent_ctx,
    child, ctxn, &inherited_all);
    if (ret)
    - break;
    + goto out_unlock;
    }

    raw_spin_lock_irqsave(&parent_ctx->lock, flags);
    @@ -8102,6 +8102,7 @@ static int perf_event_init_context(struc
    }

    raw_spin_unlock_irqrestore(&parent_ctx->lock, flags);
    +out_unlock:
    mutex_unlock(&parent_ctx->mutex);

    perf_unpin_context(parent_ctx);

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