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[18.09 backport] Masked /proc/asound #126
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@sw-pschmied originally post this in moby#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 64e52ff) Signed-off-by: Sebastiaan van Stijn <github@gone.nl>
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@thaJeztah now only privileged add-ons can play music :( |
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Backport of moby#38299 for the 18.09 branch
fixes moby#38285 for 18.09
cherry-pick was clean; no conflicts
While looking through the Moby source code was found /proc/asound to be shared
with containers as read-only.
This can lead to two information leaks.
Leak of media playback status of the host
Steps to reproduce the issue:
output
/proc/asound/card*/pcmp/sub/status | grep state | cut -d ' ' -f2 | grep
RUNNING || echo 'not running'"
host is playing music as it prints RUNNING
information regarding playback status isn't propagated instantly)
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*cinstead ofpcm*p) thiscan also leak information regarding capturing sound, as in recording
audio or making calls on the host system.