[PATCH] drm/nouveau: avoid null deref on bad arguments to nouveau_vma_getmap

[Maarten Lankhorst]

Op 28-08-13 08:29, Pasi Kärkkäinen schreef:
> On Fri, Aug 23, 2013 at 11:20:42PM +0300, Pasi Kärkkäinen wrote:
>> On Thu, Aug 22, 2013 at 09:12:40AM +0200, Maarten Lankhorst wrote:
>>> Op 22-08-13 02:10, Ilia Mirkin schreef:
>>>> The code expects non-VRAM mem nodes to have a pages list. If that's not
>>>> set, it will do a null deref down the line. Warn on that condition and
>>>> return an error.
>>>>
>>>> See https://bugs.freedesktop.org/show_bug.cgi?id=64774
>>>>
>>>> Reported-by: Pasi Kärkkäinen <pasik at iki.fi>
>>>> Tested-by: Pasi Kärkkäinen <pasik at iki.fi>
>>>> Signed-off-by: Ilia Mirkin <imirkin at alum.mit.edu>
>>>> Cc: <stable at vger.kernel.org> # 3.8+
>>>> ---
>>>>
>>>> I don't exactly understand what's going on, but this is just a
>>>> straightforward way to avoid a null deref that you see happens in the
>>>> bug. I haven't figured out the root cause of this, but it's getting
>>>> well into the "I have no idea how TTM works" space. However this seems
>>>> like a bit of defensive programming -- nouveau_vm_map_sg will pass
>>>> node->pages as a list down, which will be dereferenced by
>>>> nvc0_vm_map_sg. Perhaps the other arguments should make that
>>>> dereferencing not happen, but it definitely was happening here, as you
>>>> can see in the bug.
>>>>
>>>> Ben/Maarten, I'll let you judge whether this check is appropriate,
>>>> since like I hope I was able to convey above, I'm just not really sure :)
>>> Not it really isn't appropriate..
>>>
>>> You'd have to call call nouveau_vm_map_sg_table instead, the only place that doesn't handle that correctly
>>> is where it's not expected to be called.
>>>
>>> Here, have a completely untested patch to fix things...
>>>
>> Maarten: I've been testing this stuff with Linux 3.10.x, so I had to modify the patch a bit to make it apply there.. 
>> I've attached the modified copy that applies to 3.10.9, hopefully I did the backport correctly.
>>
>> With Linux 3.10.9 and the patch applied the kernel doesn't crash anymore, and I get this error in dmesg:
>>
>> [   76.105643] nouveau W[     DRM] Trying to create a fb in vram with valid_domains=00000004
>>
>> Does that help? 
>>
> Any comments? 
>
> Maarten's patch works for me, I get that warning instead of a kernel crash,
> but it's also a bigger change that doesn't apply to older kernels as-is. 
>
> Ilia's original patch in this thread can be applied to older kernels as-is,
> and it also prevents the kernel crash from happening.
>
> Should we get both applied, so Ilia's patch can be CC'd to stable ? 
>
You haven't understood the root cause then. You're trying to move an IMPORTED dma-buf into VRAM.
Doing so would seem to work, but at that point it's no longer a dma-buf so changes done by the exporter
would not show up in nouveau because they no longer refer to the same piece of memory.

Failing is the only right option here.

~Maarten