On Mon, 2014-05-12 at 20:45 +0000, Thomas Gleixner wrote:
> We happily allow userspace to declare a random kernel thread to be the
> owner of a user space PI futex.
>
> Found while analysing the fallout of Dave Jones syscall fuzzer.
>
> Signed-off-by: Thomas Gleixner <t...@linutronix.de>
> Cc: sta...@vger.kernel.org
> ---
> kernel/futex.c | 7 +++++++
> 1 file changed, 7 insertions(+)
>
> Index: linux-2.6/kernel/futex.c
> ===================================================================
> --- linux-2.6.orig/kernel/futex.c
> +++ linux-2.6/kernel/futex.c
> @@ -682,6 +682,8 @@ static struct task_struct * futex_find_g
> p = find_task_by_vpid(pid);
> if (p)
> get_task_struct(p);
> + else
> + p = NULL;
>
> rcu_read_unlock();
>
> @@ -814,6 +816,11 @@ lookup_pi_state(u32 uval, struct futex_h
> if (!p)
> return -ESRCH;
>
> + if (!p->mm) {
> + put_task_struct(p);
> + return -EPERM;
> + }
It might make sense to check the mm inside futex_find_get_task(), and
simply never take the refcount if NULL.
Thanks,
Davidlohr
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