From: Daniel Vetter daniel.vetter@ffwll.ch

commit 4b848f20eda5974020f043ca14bacf7a7e634fc8 upstream.

There's two references floating around here (for the object reference, not the handle_count reference, that's a different thing):

- The temporary reference held by vgem_gem_create, acquired by creating the object and released by calling drm_gem_object_put_unlocked.

- The reference held by the object handle, created by drm_gem_handle_create. This one generally outlives the function, except if a 2nd thread races with a GEM_CLOSE ioctl call.

So usually everything is correct, except in that race case, where the access to gem_object->size could be looking at freed data already. Which again isn't a real problem (userspace shot its feet off already with the race, we could return garbage), but maybe someone can exploit this as an information leak.

Cc: Dan Carpenter dan.carpenter@oracle.com Cc: Hillf Danton hdanton@sina.com Reported-by: syzbot+0dc4444774d419e916c8@syzkaller.appspotmail.com Cc: stable@vger.kernel.org Cc: Emil Velikov emil.velikov@collabora.com Cc: Daniel Vetter daniel.vetter@ffwll.ch Cc: Sean Paul seanpaul@chromium.org Cc: Chris Wilson chris@chris-wilson.co.uk Cc: Eric Anholt eric@anholt.net Cc: Sam Ravnborg sam@ravnborg.org Cc: Rob Clark robdclark@chromium.org Reviewed-by: Chris Wilson chris@chris-wilson.co.uk Signed-off-by: Daniel Vetter daniel.vetter@intel.com Link: https://patchwork.freedesktop.org/patch/msgid/20200202132133.1891846-1-danie... [OP: backport to 4.14: adjusted DRM_DEBUG() -> DRM_DEBUG_DRIVER()] Signed-off-by: Ovidiu Panait ovidiu.panait@windriver.com --- drivers/gpu/drm/vgem/vgem_drv.c | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/vgem/vgem_drv.c b/drivers/gpu/drm/vgem/vgem_drv.c index 67037eb9a80e..a1f976270a89 100644 --- a/drivers/gpu/drm/vgem/vgem_drv.c +++ b/drivers/gpu/drm/vgem/vgem_drv.c @@ -190,9 +190,10 @@ static struct drm_gem_object *vgem_gem_create(struct drm_device *dev, return ERR_CAST(obj);

ret = drm_gem_handle_create(file, &obj->base, handle); - drm_gem_object_put_unlocked(&obj->base); - if (ret) + if (ret) { + drm_gem_object_put_unlocked(&obj->base); return ERR_PTR(ret); + }

return &obj->base; } @@ -215,7 +216,9 @@ static int vgem_gem_dumb_create(struct drm_file *file, struct drm_device *dev, args->size = gem_object->size; args->pitch = pitch;

- DRM_DEBUG_DRIVER("Created object of size %lld\n", size); + drm_gem_object_put_unlocked(gem_object); + + DRM_DEBUG_DRIVER("Created object of size %llu\n", args->size);

return 0; }