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drm: rework SET_MASTER and DROP_MASTER perm handling

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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
This commit is contained in:
Emil Velikov
2020-03-19 17:29:29 +00:00
committed by Emil Velikov
parent c7ccc1b783
commit 45bc3d26c9
3 changed files with 80 additions and 2 deletions
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11
include/drm/drm_file.h
View File

@@ -201,6 +201,17 @@ struct drm_file {
*/
bool writeback_connectors;
/**
* @was_master:
*
* This client has or had, master capability. Protected by struct
* &drm_device.master_mutex.
*
* This is used to ensure that CAP_SYS_ADMIN is not enforced, if the
* client is or was master in the past.
*/
bool was_master;
/**
* @is_master:
*