[1.1] runc run: fix mount leak #4425
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When preparing to mount container root, we need to make its parent mount private (i.e. disable propagation), otherwise the new in-container mounts are leaked to the host. To find a parent mount, we use to read mountinfo and find the longest entry which can be a parent of the container root directory. Unfortunately, due to kernel bug in all Linux kernels older than v5.8 (see [1], [2]), sometimes mountinfo can't be read in its entirety. In this case, getParentMount may occasionally return a wrong parent mount. As a result, we do not change the mount propagation to private, and container mounts are leaked. Alas, we can not fix the kernel, and reading mountinfo a few times to ensure its consistency (like it's done in, say, Kubernetes) does not look like a good solution for performance reasons. Fortunately, we don't need mountinfo. Let's just traverse the directory tree, trying to remount it private until we find a mount point (any error other than EINVAL means we just found it). Fixes issue 2404. [1]: https://github.com/kolyshkin/procfs-test [2]: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=9f6c61f96f2d97cbb5f Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com> (cherry picked from commit 13a6f56) Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>
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cyphar
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Oct 3, 2024
AkihiroSuda
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This is a backport of #4417 to release-1.1.
When preparing to mount container root, we need to make its parent mount private (i.e. disable propagation), otherwise the new in-container mounts are leaked to the host.
To find a parent mount, we use to read mountinfo and find the longest entry which can be a parent of the container root directory.
Unfortunately, due to kernel bug in all Linux kernels older than v5.8 (see 1, 2), sometimes mountinfo can't be read in its entirety. In this case, getParentMount may occasionally return a wrong parent mount.
As a result, we do not change the mount propagation to private, and container mounts are leaked.
Alas, we can not fix the kernel, and reading mountinfo a few times to ensure its consistency (like it's done in, say, Kubernetes) does not look like a good solution for performance reasons.
Fortunately, we don't need mountinfo. Let's just traverse the directory tree, trying to remount it private until we find a mount point (any error other than EINVAL means we just found it).
Fixes issue 2404.
Signed-off-by: Kir Kolyshkin kolyshkin@gmail.com
(cherry picked from commit 13a6f56)
Signed-off-by: Kir Kolyshkin kolyshkin@gmail.com