2022-11-30 19:16:22

by Rob Clark

Subject: [PATCH v2 1/2] drm/shmem-helper: Remove errant put in error path

From: Rob Clark <[email protected]>

drm_gem_shmem_mmap() doesn't own this reference, resulting in the GEM
object getting prematurely freed leading to a later use-after-free.

Link: https://syzkaller.appspot.com/bug?extid=c8ae65286134dd1b800d
Reported-by: [email protected]
Fixes: 2194a63a818d ("drm: Add library for shmem backed GEM objects")
Cc: [email protected]
Signed-off-by: Rob Clark <[email protected]>
Reviewed-by: Daniel Vetter <[email protected]>
---
drivers/gpu/drm/drm_gem_shmem_helper.c | 4 +---
1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c b/drivers/gpu/drm/drm_gem_shmem_helper.c
index 35138f8a375c..3b7b71391a4c 100644
--- a/drivers/gpu/drm/drm_gem_shmem_helper.c
+++ b/drivers/gpu/drm/drm_gem_shmem_helper.c
@@ -622,10 +622,8 @@ int drm_gem_shmem_mmap(struct drm_gem_shmem_object *shmem, struct vm_area_struct
}

ret = drm_gem_shmem_get_pages(shmem);
- if (ret) {
- drm_gem_vm_close(vma);
+ if (ret)
return ret;
- }

vma->vm_flags |= VM_PFNMAP | VM_DONTEXPAND | VM_DONTDUMP;
vma->vm_page_prot = vm_get_page_prot(vma->vm_flags);
--
2.38.1

2022-12-04 20:53:29

by Dmitry Osipenko

Subject: Re: [PATCH v2 1/2] drm/shmem-helper: Remove errant put in error path

On 11/30/22 21:57, Rob Clark wrote:
> From: Rob Clark <[email protected]>
>
> drm_gem_shmem_mmap() doesn't own this reference, resulting in the GEM
> object getting prematurely freed leading to a later use-after-free.
>
> Link: https://syzkaller.appspot.com/bug?extid=c8ae65286134dd1b800d
> Reported-by: [email protected]
> Fixes: 2194a63a818d ("drm: Add library for shmem backed GEM objects")
> Cc: [email protected]
> Signed-off-by: Rob Clark <[email protected]>
> Reviewed-by: Daniel Vetter <[email protected]>
> ---
> drivers/gpu/drm/drm_gem_shmem_helper.c | 4 +---
> 1 file changed, 1 insertion(+), 3 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c b/drivers/gpu/drm/drm_gem_shmem_helper.c
> index 35138f8a375c..3b7b71391a4c 100644
> --- a/drivers/gpu/drm/drm_gem_shmem_helper.c
> +++ b/drivers/gpu/drm/drm_gem_shmem_helper.c
> @@ -622,10 +622,8 @@ int drm_gem_shmem_mmap(struct drm_gem_shmem_object *shmem, struct vm_area_struct
> }
>
> ret = drm_gem_shmem_get_pages(shmem);
> - if (ret) {
> - drm_gem_vm_close(vma);
> + if (ret)
> return ret;
> - }
>
> vma->vm_flags |= VM_PFNMAP | VM_DONTEXPAND | VM_DONTDUMP;
> vma->vm_page_prot = vm_get_page_prot(vma->vm_flags);

AFAICS, the dmabuf mmaping code path needs a similar fix, isn't it?

- /* Drop the reference drm_gem_mmap_obj() acquired.*/
- drm_gem_object_put(obj);
vma->vm_private_data = NULL;

- return dma_buf_mmap(obj->dma_buf, vma, 0);
+ ret = dma_buf_mmap(obj->dma_buf, vma, 0);
+
+ /* Drop the reference drm_gem_mmap_obj() acquired.*/
+ if (!ret)
+ drm_gem_object_put(obj);
+
+ return ret;


--
Best regards,
Dmitry

2022-12-06 18:20:55

by Rob Clark

Subject: Re: [PATCH v2 1/2] drm/shmem-helper: Remove errant put in error path

On Sun, Dec 4, 2022 at 12:45 PM Dmitry Osipenko
<[email protected]> wrote:
>
> On 11/30/22 21:57, Rob Clark wrote:
> > From: Rob Clark <[email protected]>
> >
> > drm_gem_shmem_mmap() doesn't own this reference, resulting in the GEM
> > object getting prematurely freed leading to a later use-after-free.
> >
> > Link: https://syzkaller.appspot.com/bug?extid=c8ae65286134dd1b800d
> > Reported-by: [email protected]
> > Fixes: 2194a63a818d ("drm: Add library for shmem backed GEM objects")
> > Cc: [email protected]
> > Signed-off-by: Rob Clark <[email protected]>
> > Reviewed-by: Daniel Vetter <[email protected]>
> > ---
> > drivers/gpu/drm/drm_gem_shmem_helper.c | 4 +---
> > 1 file changed, 1 insertion(+), 3 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c b/drivers/gpu/drm/drm_gem_shmem_helper.c
> > index 35138f8a375c..3b7b71391a4c 100644
> > --- a/drivers/gpu/drm/drm_gem_shmem_helper.c
> > +++ b/drivers/gpu/drm/drm_gem_shmem_helper.c
> > @@ -622,10 +622,8 @@ int drm_gem_shmem_mmap(struct drm_gem_shmem_object *shmem, struct vm_area_struct
> > }
> >
> > ret = drm_gem_shmem_get_pages(shmem);
> > - if (ret) {
> > - drm_gem_vm_close(vma);
> > + if (ret)
> > return ret;
> > - }
> >
> > vma->vm_flags |= VM_PFNMAP | VM_DONTEXPAND | VM_DONTDUMP;
> > vma->vm_page_prot = vm_get_page_prot(vma->vm_flags);
>
> AFAICS, the dmabuf mmaping code path needs a similar fix, isn't it?
>
> - /* Drop the reference drm_gem_mmap_obj() acquired.*/
> - drm_gem_object_put(obj);
> vma->vm_private_data = NULL;
>
> - return dma_buf_mmap(obj->dma_buf, vma, 0);
> + ret = dma_buf_mmap(obj->dma_buf, vma, 0);
> +
> + /* Drop the reference drm_gem_mmap_obj() acquired.*/
> + if (!ret)
> + drm_gem_object_put(obj);
> +
> + return ret;
>

Yes, it seems that way.. I wish the shmem helpers worked in a less
"special" way with regards to refcnting :-(

BR,
-R