rootfs: umount all procfs and sysfs with --no-pivot #1962
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LGTM |
AkihiroSuda
reviewed
Jan 12, 2019
libcontainer/rootfs_linux.go
Outdated
| return err | ||
| } | ||
| if err := unix.Unmount(p, unix.MNT_DETACH); err != nil { | ||
| if err.(syscall.Errno) != unix.EINVAL { |
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Potentially we can also get EPERM here?
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I guess, but I never saw that error message, when trying to umount /proc or /sys I got only EINVAL. I can amend the patch if you'd like
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I went forward and amended the change in the updated version
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cyphar
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Jan 14, 2019
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>
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LGTM |
AkihiroSuda
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Jan 15, 2019
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LGTM. |
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Changes: opencontainers/runc@96ec217...12f6a99 Including critical security fix for `runc run --no-pivot` (`DOCKER_RAMDISK=1`): opencontainers/runc#1962 Signed-off-by: Akihiro Suda <suda.akihiro@lab.ntt.co.jp>
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Including critical security fix for `runc run --no-pivot` (unlikely to affect BuildKit): opencontainers/runc#1962 Signed-off-by: Akihiro Suda <suda.akihiro@lab.ntt.co.jp>
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Changes: opencontainers/runc@96ec217...12f6a99 Including critical security fix for `runc run --no-pivot` (`DOCKER_RAMDISK=1`): opencontainers/runc#1962 Signed-off-by: Akihiro Suda <suda.akihiro@lab.ntt.co.jp>
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Changes: opencontainers/runc@96ec217...12f6a99 Including critical security fix for `runc run --no-pivot` (`DOCKER_RAMDISK=1`): opencontainers/runc#1962 Signed-off-by: Akihiro Suda <suda.akihiro@lab.ntt.co.jp> (cherry picked from commit 3aec9e7)
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Changes: opencontainers/runc@96ec217...12f6a99 Including critical security fix for `runc run --no-pivot` (`DOCKER_RAMDISK=1`): opencontainers/runc#1962 Signed-off-by: Akihiro Suda <suda.akihiro@lab.ntt.co.jp> (cherry picked from commit 1ee33f4)
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Changes: opencontainers/runc@96ec217...12f6a99 Including critical security fix for `runc run --no-pivot` (`DOCKER_RAMDISK=1`): opencontainers/runc#1962 Signed-off-by: Akihiro Suda <suda.akihiro@lab.ntt.co.jp> (cherry picked from commit 3aec9e7) Signed-off-by: Akihiro Suda <suda.akihiro@lab.ntt.co.jp>
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Changes: opencontainers/runc@69663f0...12f6a99 Including critical security fix for `runc run --no-pivot` (`DOCKER_RAMDISK=1`): opencontainers/runc#1962 Signed-off-by: Akihiro Suda <suda.akihiro@lab.ntt.co.jp>
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Changes: opencontainers/runc@96ec217...12f6a99 Including critical security fix for `runc run --no-pivot` (`DOCKER_RAMDISK=1`): opencontainers/runc#1962 Signed-off-by: Akihiro Suda <suda.akihiro@lab.ntt.co.jp>
kolyshkin
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Mar 13, 2020
| return err | ||
| } | ||
|
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| absRootfs, err := filepath.Abs(rootfs) |
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AFAICS this is not needed since rootfs is already validated by (*ConfigValidator).rootfs()
kolyshkin
reviewed
Mar 13, 2020
| } | ||
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| for _, info := range mountinfos { | ||
| p, err := filepath.Abs(info.Mountpoint) |
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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