[PATCH 0/2] dlm: restrict userspace control devices to CAP_SYS_ADMIN

[Haofeng Li]

The DLM plock and monitor miscdevices are control interfaces intended
for privileged userspace daemons, but neither currently checks the
caller's capabilities when the device is opened.

devtmpfs creates both device nodes with mode 0600 by default.  Relying
only on that mode, however, leaves the interfaces unprotected if a node
is exposed through a changed udev rule, a container bind mount, or a
passed file descriptor.  An opener of dlm_plock can consume pending
requests and submit forged results.  An opener of dlm-monitor can alter
the global monitor reference count; the last close stops all local
lockspaces.

Require CAP_SYS_ADMIN in both open paths and explicitly set the device
mode to 0600.  The individual patches contain reproduction details for
each interface.

Haofeng Li (2):
  dlm: gate dlm_plock device on CAP_SYS_ADMIN
  dlm: require CAP_SYS_ADMIN for dlm-monitor device

 fs/dlm/plock.c | 14 +++++++++++++-
 fs/dlm/user.c  |  6 ++++++
 2 files changed, 19 insertions(+), 1 deletion(-)


base-commit: a13c140cc289c0b7b3770bce5b3ad42ab35074aa
-- 
2.25.1