redonkable
/
alistair23-linux
1
0
Fork 0
Code Releases Activity

drm/vgem: Close use-after-free race in vgem_gem_create 

commit 4b848f20ed 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-daniel.vetter@ffwll.ch
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
5.4-rM2-2.2.x-imx-squashed
Daniel Vetter 2020-02-02 14:21:33 +01:00 committed by Greg Kroah-Hartman
parent 9ea6651591
commit 3ea7f138ce
1 changed files with 6 additions and 3 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

9
drivers/gpu/drm/vgem/vgem_drv.c
View File

@ -196,9 +196,10 @@ 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;
}
@ -221,7 +222,9 @@ static int vgem_gem_dumb_create(struct drm_file *file, struct drm_device *dev,
args->size = gem_object->size;
args->pitch = pitch;
DRM_DEBUG("Created object of size %lld\n", size);
drm_gem_object_put_unlocked(gem_object);
DRM_DEBUG("Created object of size %llu\n", args->size);
return 0;
}