| Date | Tue, 30 Mar 2010 15:48:25 -0700 | From | Greg KH <> | Subject | [05/45] futex: Handle user space corruption gracefully |
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2.6.27-stable review patch. If anyone has any objections, please let us know.
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From: Thomas Gleixner <tglx@linutronix.de>
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 <jmarchan@redhat.com> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Acked-by: Darren Hart <dvhltc@us.ibm.com> Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
--- kernel/futex.c | 7 +++++++ 1 file changed, 7 insertions(+)
--- a/kernel/futex.c +++ b/kernel/futex.c @@ -647,6 +647,13 @@ 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; + spin_lock(&pi_state->pi_mutex.wait_lock); new_owner = rt_mutex_next_owner(&pi_state->pi_mutex);
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