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

[Maarten Lankhorst <maarten.lankhorst@canonical.com>]

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@iki.fi>
> Tested-by: Pasi Kärkkäinen <pasik@iki.fi>
> Signed-off-by: Ilia Mirkin <imirkin@alum.mit.edu>
> Cc: <stable@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...

diff --git a/drivers/gpu/drm/nouveau/nouveau_display.c b/drivers/gpu/drm/nouveau/nouveau_display.c
--- a/drivers/gpu/drm/nouveau/nouveau_display.c
+++ b/drivers/gpu/drm/nouveau/nouveau_display.c
@@ -138,17 +143,26 @@ nouveau_user_framebuffer_create(struct drm_device *dev,
 {
 	struct nouveau_framebuffer *nouveau_fb;
 	struct drm_gem_object *gem;
+	struct nouveau_bo *nvbo;
 	int ret = -ENOMEM;
 
 	gem = drm_gem_object_lookup(dev, file_priv, mode_cmd->handles[0]);
 	if (!gem)
 		return ERR_PTR(-ENOENT);
 
+	nvbo = nouveau_gem_object(gem);
+	if (!(nvbo->valid_domains & NOUVEAU_GEM_DOMAIN_VRAM)) {
+		nv_warn(nouveau_drm(dev), "Trying to create a fb in vram with"
+			" valid_domains=%08x\n", nvbo->valid_domains);
+		ret = -EINVAL;
+		goto err_unref;
+	}
+
 	nouveau_fb = kzalloc(sizeof(struct nouveau_framebuffer), GFP_KERNEL);
 	if (!nouveau_fb)
 		goto err_unref;
 
-	ret = nouveau_framebuffer_init(dev, nouveau_fb, mode_cmd, nouveau_gem_object(gem));
+	ret = nouveau_framebuffer_init(dev, nouveau_fb, mode_cmd, nvbo);
 	if (ret)
 		goto err;
 

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