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    Subject[03/93] futex: Handle user space corruption gracefully
    2.6.32-stable review patch.  If anyone has any objections, please let us know.


    From: Thomas Gleixner <>

    commit 51246bfd189064079c54421507236fd2723b18f3 upstream.

    If the owner of a PI futex dies we fix up the pi_state and set
    pi_state->owner to NULL. When a malicious or just sloppy programmed
    user space application sets the futex value to 0 e.g. by calling
    pthread_mutex_init(), then the futex can be acquired again. A new
    waiter manages to enqueue itself on the pi_state w/o damage, but on
    unlock the kernel dereferences pi_state->owner and oopses.

    Prevent this by checking pi_state->owner in the unlock path. If
    pi_state->owner is not current we know that user space manipulated the
    futex value. Ignore the mess and return -EINVAL.

    This catches the above case and also the case where a task hijacks the
    futex by setting the tid value and then tries to unlock it.

    Reported-by: Jermome Marchand <>
    Signed-off-by: Thomas Gleixner <>
    Acked-by: Darren Hart <>
    Acked-by: Peter Zijlstra <>
    Signed-off-by: Greg Kroah-Hartman <>

    kernel/futex.c | 7 +++++++
    1 file changed, 7 insertions(+)

    --- a/kernel/futex.c
    +++ b/kernel/futex.c
    @@ -758,6 +758,13 @@ static int wake_futex_pi(u32 __user *uad
    if (!pi_state)
    return -EINVAL;

    + /*
    + * If current does not own the pi_state then the futex is
    + * inconsistent and user space fiddled with the futex value.
    + */
    + if (pi_state->owner != current)
    + return -EINVAL;
    new_owner = rt_mutex_next_owner(&pi_state->pi_mutex);

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      Last update: 2010-02-19 18:03    [W:0.021 / U:18.948 seconds]
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