linux-kernel - Re: [PATCH v3 05/15] habanalabs: add command buffer module

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Date:   Sat, 9 Feb 2019 10:09:49 +0100
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Oded Gabbay <oded.gabbay@...il.com>
Cc:     "Linux-Kernel@...r. Kernel. Org" <linux-kernel@...r.kernel.org>,
        Olof Johansson <olof@...om.net>,
        Mike Rapoport <rppt@...ux.ibm.com>, ogabbay@...ana.ai,
        Arnd Bergmann <arnd@...db.de>, Joe Perches <joe@...ches.com>
Subject: Re: [PATCH v3 05/15] habanalabs: add command buffer module

On Fri, Feb 08, 2019 at 09:53:27PM +0200, Oded Gabbay wrote:
> On Fri, Feb 8, 2019 at 2:06 PM Greg KH <gregkh@...uxfoundation.org> wrote:
> >
> > On Mon, Feb 04, 2019 at 10:32:44PM +0200, Oded Gabbay wrote:
> > > +int hl_cb_ioctl(struct hl_fpriv *hpriv, void *data)
> > > +{
> > > +     union hl_cb_args *args = data;
> > > +     struct hl_device *hdev = hpriv->hdev;
> > > +     u64 handle;
> > > +     int rc;
> > > +
> > > +     switch (args->in.op) {
> > > +     case HL_CB_OP_CREATE:
> > > +             rc = hl_cb_create(hdev, &hpriv->cb_mgr, args->in.cb_size,
> > > +                                     &handle, hpriv->ctx->asid);
> >
> > so cb_size comes from userspace, ok, you check for the value to be too
> > small, but not too big.  That means someone can try to allocate too much
> > memory, possibly crashing things, not good :(
> Yes, correct, but even if I limit a single allocation to, let's say,
> 1MB, what's stopping a userspace process from allocating multiple CBs
> and draining the system memory ? I'm counting on the oom module to
> kill that process if it mis-behaves.
> And, btw, I assumed there is hard limit of 4MB on a single
> dma_alloc_coherent. i.e. I was never able to allocate more then 4MB
> through that API. So I never thought I need to check for max size
> because of that hard limit.
> Am I missing something here ?

Relying on the oom module to handle driver issues is not always a wise
idea ;)

You should put a bounds on your max allocation, if it really is 4MB,
then test for that.

thanks,

greg k-h