thinkpad-acpi: lock down video output state access
Given the right combination of ThinkPad and X.org, just reading the
video output control state is enough to hard-crash X.org.
Until the day I somehow find out a model or BIOS cut date to not
provide this feature to ThinkPads that can do video switching through
X RandR, change permissions so that only processes with CAP_SYS_ADMIN
can access any sort of video output control state.
This bug could be considered a local DoS I suppose, as it allows any
non-privledged local user to cause some versions of X.org to
hard-crash some ThinkPads.
Reported-by: Jidanni <jidanni@jidanni.org>
Signed-off-by: Henrique de Moraes Holschuh <hmh@hmh.eng.br>
Cc: stable@kernel.org
diff --git a/drivers/platform/x86/Kconfig b/drivers/platform/x86/Kconfig
index f526e73..11fce79 100644
--- a/drivers/platform/x86/Kconfig
+++ b/drivers/platform/x86/Kconfig
@@ -319,9 +319,15 @@
server running, phase of the moon, and the current mood of
Schroedinger's cat. If you can use X.org's RandR to control
your ThinkPad's video output ports instead of this feature,
- don't think twice: do it and say N here to save some memory.
+ don't think twice: do it and say N here to save memory and avoid
+ bad interactions with X.org.
- If you are not sure, say Y here.
+ NOTE: access to this feature is limited to processes with the
+ CAP_SYS_ADMIN capability, to avoid local DoS issues in platforms
+ where it interacts badly with X.org.
+
+ If you are not sure, say Y here but do try to check if you could
+ be using X.org RandR instead.
config THINKPAD_ACPI_HOTKEY_POLL
bool "Support NVRAM polling for hot keys"