On Sun, Dec 4, 2022 at 12:45 PM Dmitry Osipenko <dmitry.osipenko@xxxxxxxxxxxxx> wrote: > > On 11/30/22 21:57, Rob Clark wrote: > > From: Rob Clark <robdclark@xxxxxxxxxxxx> > > > > 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: syzbot+c8ae65286134dd1b800d@xxxxxxxxxxxxxxxxxxxxxxxxx > > Fixes: 2194a63a818d ("drm: Add library for shmem backed GEM objects") > > Cc: stable@xxxxxxxxxxxxxxx > > Signed-off-by: Rob Clark <robdclark@xxxxxxxxxxxx> > > Reviewed-by: Daniel Vetter <daniel.vetter@xxxxxxxx> > > --- > > 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
