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[18.06 backport] rootfs: umount all procfs and sysfs with --no-pivot #11
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When creating a new user namespace, the kernel doesn't allow to mount a new procfs or sysfs file system if there is not already one instance fully visible in the current mount namespace. When using --no-pivot we were effectively inhibiting this protection from the kernel, as /proc and /sys from the host are still present in the container mount namespace. A container without full access to /proc could then create a new user namespace, and from there able to mount a fully visible /proc, bypassing the limitations in the container. A simple reproducer for this issue is: unshare -mrfp sh -c "mount -t proc none /proc && echo c > /proc/sysrq-trigger" Signed-off-by: Giuseppe Scrivano <gscrivan@redhat.com> (cherry picked from commit 28a697c) Signed-off-by: Sebastiaan van Stijn <github@gone.nl>
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ping @justincormack @kolyshkin @andrewhsu PTAL |
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Backport of opencontainers#1962 for 18.06.
cherry-pick was clean; no conflicts
When creating a new user namespace, the kernel doesn't allow to mount
a new procfs or sysfs file system if there is not already one instance
fully visible in the current mount namespace.
When using --no-pivot we were effectively inhibiting this protection
from the kernel, as /proc and /sys from the host are still present in
the container mount namespace.
A container without full access to /proc could then create a new user
namespace, and from there able to mount a fully visible /proc, bypassing
the limitations in the container.
A simple reproducer for this issue is:
unshare -mrfp sh -c "mount -t proc none /proc && echo c > /proc/sysrq-trigger"
Signed-off-by: Giuseppe Scrivano gscrivan@redhat.com
(cherry picked from commit 28a697c)
Signed-off-by: Sebastiaan van Stijn github@gone.nl