|From:||Greg KH <gregkh-AT-suse.de>|
|Subject:||[03/93] futex: Handle user space corruption gracefully|
|Date:||Fri, 19 Feb 2010 08:28:56 -0800|
|Cc:||stable-review-AT-kernel.org, torvalds-AT-linux-foundation.org, akpm-AT-linux-foundation.org, alan-AT-lxorguk.ukuu.org.uk, Thomas Gleixner <tglx-AT-linutronix.de>, Darren Hart <dvhltc-AT-us.ibm.com>, Peter Zijlstra <a.p.zijlstra-AT-chello.nl>|
2.6.32-stable review patch. If anyone has any objections, please let us know. ------------------ From: Thomas Gleixner <email@example.com> 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 <firstname.lastname@example.org> Signed-off-by: Thomas Gleixner <email@example.com> Acked-by: Darren Hart <firstname.lastname@example.org> Acked-by: Peter Zijlstra <email@example.com> Signed-off-by: Greg Kroah-Hartman <firstname.lastname@example.org> --- 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; + spin_lock(&pi_state->pi_mutex.wait_lock); new_owner = rt_mutex_next_owner(&pi_state->pi_mutex);
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