From 8244a3bc27b3efd057da154b8d7e414670d5044f Mon Sep 17 00:00:00 2001 From: Anand K Mistry Date: Thu, 30 Sep 2021 09:00:07 +1000 Subject: drm/prime: Fix use after free in mmap with drm_gem_ttm_mmap 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 Fixes: 9786b65bc61a ("drm/ttm: fix mmap refcounting") Cc: Gerd Hoffmann Cc: Daniel Vetter Cc: Maarten Lankhorst Cc: Maxime Ripard Cc: Thomas Zimmermann Cc: David Airlie Cc: Daniel Vetter Cc: dri-devel@lists.freedesktop.org Cc: # v5.5+ Signed-off-by: Thomas Zimmermann Link: https://patchwork.freedesktop.org/patch/msgid/20210930085932.1.I8043d61cc238e0168e2f4ca5f4783223434aa587@changeid --- drivers/gpu/drm/drm_prime.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) (limited to 'drivers/gpu/drm/drm_prime.c') diff --git a/drivers/gpu/drm/drm_prime.c b/drivers/gpu/drm/drm_prime.c index deb23dbec8b5..d6c7f4f9a7a2 100644 --- a/drivers/gpu/drm/drm_prime.c +++ b/drivers/gpu/drm/drm_prime.c @@ -719,11 +719,13 @@ int drm_gem_prime_mmap(struct drm_gem_object *obj, struct vm_area_struct *vma) if (obj->funcs && obj->funcs->mmap) { vma->vm_ops = obj->funcs->vm_ops; + 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; } -- cgit v1.2.3