2019-11-06 07:32:38

by Pan Bian

[permalink] [raw]

Subject: [PATCH] drm/i915/gvt: fix dropping obj reference twice

---

The reference count of obj will be decremented twice if error occurs
in dma_buf_fd(). Additionally, attempting to read the reference count of
obj after dropping reference may lead to a use after free bug. Here, we
drop obj's reference until it is not used.

Signed-off-by: Pan Bian <[email protected]>
---
drivers/gpu/drm/i915/gvt/dmabuf.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/i915/gvt/dmabuf.c b/drivers/gpu/drm/i915/gvt/dmabuf.c
index 13044c027f27..4bfaefdf548d 100644
--- a/drivers/gpu/drm/i915/gvt/dmabuf.c
+++ b/drivers/gpu/drm/i915/gvt/dmabuf.c
@@ -498,8 +498,6 @@ int intel_vgpu_get_dmabuf(struct intel_vgpu *vgpu, unsigned int dmabuf_id)
goto out_free_gem;
}

- i915_gem_object_put(obj);
-
ret = dma_buf_fd(dmabuf, DRM_CLOEXEC | DRM_RDWR);
if (ret < 0) {
gvt_vgpu_err("create dma-buf fd failed ret:%d\n", ret);
@@ -524,6 +522,8 @@ int intel_vgpu_get_dmabuf(struct intel_vgpu *vgpu, unsigned int dmabuf_id)
file_count(dmabuf->file),
kref_read(&obj->base.refcount));

+ i915_gem_object_put(obj);
+
return dmabuf_fd;

out_free_dmabuf:
--
2.7.4

2019-11-06 08:45:13

by Zhenyu Wang

[permalink] [raw]

Subject: Re: [PATCH] drm/i915/gvt: fix dropping obj reference twice

---

On 2019.11.06 15:31:07 +0800, Pan Bian wrote:
> The reference count of obj will be decremented twice if error occurs
> in dma_buf_fd(). Additionally, attempting to read the reference count of
> obj after dropping reference may lead to a use after free bug. Here, we
> drop obj's reference until it is not used.
>
> Signed-off-by: Pan Bian <[email protected]>
> ---
> drivers/gpu/drm/i915/gvt/dmabuf.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/gvt/dmabuf.c b/drivers/gpu/drm/i915/gvt/dmabuf.c
> index 13044c027f27..4bfaefdf548d 100644
> --- a/drivers/gpu/drm/i915/gvt/dmabuf.c
> +++ b/drivers/gpu/drm/i915/gvt/dmabuf.c
> @@ -498,8 +498,6 @@ int intel_vgpu_get_dmabuf(struct intel_vgpu *vgpu, unsigned int dmabuf_id)
> goto out_free_gem;
> }
>
> - i915_gem_object_put(obj);
> -
> ret = dma_buf_fd(dmabuf, DRM_CLOEXEC | DRM_RDWR);
> if (ret < 0) {
> gvt_vgpu_err("create dma-buf fd failed ret:%d\n", ret);
> @@ -524,6 +522,8 @@ int intel_vgpu_get_dmabuf(struct intel_vgpu *vgpu, unsigned int dmabuf_id)
> file_count(dmabuf->file),
> kref_read(&obj->base.refcount));
>
> + i915_gem_object_put(obj);
> +
> return dmabuf_fd;
>
> out_free_dmabuf:

Looks fine to me. Thanks!

Reviewed-by: Zhenyu Wang <[email protected]>

--
Open Source Technology Center, Intel ltd.

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