Re: [PATCH] arch/x86: fix out-of-bounds in get_wchan()

[Borislav Petkov]

On Mon, Sep 28, 2015 at 11:49:18AM +0200, Dmitry Vyukov wrote:
> Original code did:
> 
>      if (p->thread.sp < stack || p->thread.sp >= stack+THREAD_SIZE)
>            return 0;
>      fp = *(u64 *)(p->thread.sp);
> 
> p->thread.sp can change concurrently.
> So we could check that p->thread.sp is within stack bounds, but then
> dereference another value (which is already outside of bounds).

Right, we do deref it. I realized that after hitting "Send" :\

Which begs another, probably also stupid, question:

What guarantees the task won't disappear after we've checked p?

I.e., after this:

        if (!p || p == current || p->state == TASK_RUNNING)
                return 0;

Thanks.

-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.
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