This commit reworks the permission handling of the two ioctls. In
particular it enforced the CAP_SYS_ADMIN check only, if:
- we're issuing the ioctl from process other than the one which opened
the node, and
- we are, or were master in the past
This ensures that we:
- do not regress the systemd-logind style of DRM_MASTER arbitrator
- allow applications which do not use systemd-logind to drop their
master capabilities (and regain them at later point) ... w/o running as
root.
See the comment above drm_master_check_perm() for more details.
v1:
- Tweak wording, fixup all checks, add igt test
v2:
- Add a few more comments, grammar nitpicks.
Cc: Adam Jackson <ajax@redhat.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Pekka Paalanen <ppaalanen@gmail.com>
Testcase: igt/core_setmaster/master-drop-set-user
Signed-off-by: Emil Velikov <emil.velikov@collabora.com>
Reviewed-by: Adam Jackson <ajax@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200319172930.230583-1-emil.l.velikov@gmail.com
45bc3d26c9