Masked /proc/asound
@sw-pschmied originally post this in #38285
While looking through the Moby source code was found /proc/asound to be
shared with containers as read-only (as defined in
https://github.com/moby/moby/blob/master/oci/defaults.go#L128).
This can lead to two information leaks.
---
**Leak of media playback status of the host**
Steps to reproduce the issue:
- Listen to music/Play a YouTube video/Do anything else that involves
sound output
- Execute docker run --rm ubuntu:latest bash -c "sleep 7; cat
/proc/asound/card*/pcm*p/sub*/status | grep state | cut -d ' ' -f2 |
grep RUNNING || echo 'not running'"
- See that the containerized process is able to check whether someone
on the host is playing music as it prints RUNNING
- Stop the music output
- Execute the command again (The sleep is delaying the output because
information regarding playback status isn't propagated instantly)
- See that it outputs not running
**Describe the results you received:**
A containerized process is able to gather information on the playback
status of an audio device governed by the host. Therefore a process of a
container is able to check whether and what kind of user activity is
present on the host system. Also, this may indicate whether a container
runs on a desktop system or a server as media playback rarely happens on
server systems.
The description above is in regard to media playback - when examining
`/proc/asound/card*/pcm*c/sub*/status` (`pcm*c` instead of `pcm*p`) this
can also leak information regarding capturing sound, as in recording
audio or making calls on the host system.
Signed-off-by: Jonathan A. Schweder <jonathanschweder@gmail.com>
(cherry picked from commit 64e52ff3dbdb31adc0a9930b3ea74b04b0df8d86)
Signed-off-by: Sebastiaan van Stijn <github@gone.nl>
diff --git a/oci/defaults.go b/oci/defaults.go
index 992157b..8ba9240 100644
--- a/oci/defaults.go
+++ b/oci/defaults.go
@@ -114,6 +114,7 @@
s.Linux = &specs.Linux{
MaskedPaths: []string{
+ "/proc/asound",
"/proc/acpi",
"/proc/kcore",
"/proc/keys",
@@ -125,7 +126,6 @@
"/sys/firmware",
},
ReadonlyPaths: []string{
- "/proc/asound",
"/proc/bus",
"/proc/fs",
"/proc/irq",
