From: Anand K Mistry amistry@google.com

mainline inclusion from mainline-v5.16-rc1 commit 8244a3bc27b3efd057da154b8d7e414670d5044f category: bugfix bugzilla: https://gitee.com/src-openeuler/kernel/issues/I9FNEV CVE: CVE-2021-47200

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?i...

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drm_gem_ttm_mmap() drops a reference to the gem object on success. If the gem object's refcount == 1 on entry to drm_gem_prime_mmap(), that drop will free the gem object, and the subsequent drm_gem_object_get() will be a UAF. Fix by grabbing a reference before calling the mmap helper.

This issue was forseen when the reference dropping was adding in commit 9786b65bc61ac ("drm/ttm: fix mmap refcounting"): "For that to work properly the drm_gem_object_get() call in drm_gem_ttm_mmap() must be moved so it happens before calling obj->funcs->mmap(), otherwise the gem refcount would go down to zero."

Signed-off-by: Anand K Mistry amistry@google.com Fixes: 9786b65bc61a ("drm/ttm: fix mmap refcounting") Cc: Gerd Hoffmann kraxel@redhat.com Cc: Daniel Vetter daniel.vetter@ffwll.ch Cc: Maarten Lankhorst maarten.lankhorst@linux.intel.com Cc: Maxime Ripard mripard@kernel.org Cc: Thomas Zimmermann tzimmermann@suse.de Cc: David Airlie airlied@linux.ie Cc: Daniel Vetter daniel@ffwll.ch Cc: dri-devel@lists.freedesktop.org Cc: stable@vger.kernel.org # v5.5+ Signed-off-by: Thomas Zimmermann tzimmermann@suse.de Link: https://patchwork.freedesktop.org/patch/msgid/20210930085932.1.I8043d61cc238... Conflicts: drivers/gpu/drm/drm_prime.c [Resolve conflicts due to several refactor patches not merged.] Signed-off-by: Zeng Heng zengheng4@huawei.com --- drivers/gpu/drm/drm_prime.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/drm_prime.c b/drivers/gpu/drm/drm_prime.c index 825499ea3ff5..c806cf4c9a48 100644 --- a/drivers/gpu/drm/drm_prime.c +++ b/drivers/gpu/drm/drm_prime.c @@ -724,11 +724,14 @@ int drm_gem_prime_mmap(struct drm_gem_object *obj, struct vm_area_struct *vma) vma->vm_pgoff += drm_vma_node_start(&obj->vma_node);

if (obj->funcs && obj->funcs->mmap) { + + drm_gem_object_get(obj); ret = obj->funcs->mmap(obj, vma); - if (ret) + if (ret) { + drm_gem_object_put(obj); return ret; + } vma->vm_private_data = obj; - drm_gem_object_get(obj); return 0; }