Further updates per SIG Node comments
This commit is contained in:
Robert Krawitz
parent
45bafb9542
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d0879693b3
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@ -37,6 +37,7 @@ superseded-by:
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* [Motivation](#motivation)
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* [Goals](#goals)
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* [Non-Goals](#non-goals)
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* [Future Work](#future-work)
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* [Proposal](#proposal)
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* [Control over Use of Quotas](#control-over-use-of-quotas)
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* [Operation Flow -- Applying a Quota](#operation-flow----applying-a-quota)
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@ -58,12 +59,22 @@ superseded-by:
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* [Alternative quota-based implementation](#alternative-quota-based-implementation)
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* [Alternative loop filesystem-based implementation](#alternative-loop-filesystem-based-implementation)
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* [Infrastructure Needed [optional]](#infrastructure-needed-optional)
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* [References](#references)
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* [Bugs Opened Against Filesystem Quotas](#bugs-opened-against-filesystem-quotas)
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* [CVE](#cve)
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* [Other Security Issues Without CVE](#other-security-issues-without-cve)
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* [Other Linux Quota-Related Bugs Since 2012](#other-linux-quota-related-bugs-since-2012)
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[Tools for generating]: https://github.com/ekalinin/github-markdown-toc
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## Summary
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This proposal applies to the use of quotas for ephemeral-storage
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metrics gathering. Use of quotas for ephemeral-storage limit
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enforcement is a [non-goal](#non-goals), but as the architecture and
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code will be very similar, there are comments interspersed related to
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enforcement. _These comments will be italicized_.
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Local storage capacity isolation, aka ephemeral-storage, was
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introduced into Kubernetes via
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<https://github.com/kubernetes/features/issues/361>. It provides
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@ -80,9 +91,9 @@ latency (i. e. a pod could consume a lot of storage prior to the
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kubelet being aware of its overage and terminating it).
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The mechanism proposed here utilizes filesystem project quotas to
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provide monitoring of resource consumption and optionally enforcement
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of limits. Project quotas, initially in XFS and more recently ported
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to ext4fs, offer a kernel-based means of restricting and monitoring
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provide monitoring of resource consumption _and optionally enforcement
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of limits._ Project quotas, initially in XFS and more recently ported
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to ext4fs, offer a kernel-based means of monitoring _and restricting_
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filesystem consumption that can be applied to one or more directories.
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A prototype is in progress; see <https://github.com/kubernetes/kubernetes/pull/66928>.
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@ -107,7 +118,7 @@ total blocks and inodes for all files with the given project ID are
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maintained by the kernel. Project quotas can be managed from
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userspace by means of the `xfs_quota(8)` command in foreign filesystem
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(`-f`) mode; the traditional Linux quota tools do not manipulate
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project quotas. Programmatically, they are managed by the quotactl(2)
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project quotas. Programmatically, they are managed by the `quotactl(2)`
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system call, using in part the standard quota commands and in part the
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XFS quota commands; the man page implies incorrectly that the XFS
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quota commands apply only to XFS filesystems.
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@ -115,7 +126,7 @@ quota commands apply only to XFS filesystems.
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The project ID applied to a directory is inherited by files created
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under it. Files cannot be (hard) linked across directories with
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different project IDs. A file's project ID cannot be changed by a
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non-privileged user, but a privileged user may use the xfs_io(8)
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non-privileged user, but a privileged user may use the `xfs_io(8)`
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command to change the project ID of a file.
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Filesystems using project quotas may be mounted with quotas either
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@ -134,9 +145,10 @@ from project ID to directory/file; this can be a one to many mapping
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any given directory/file can be assigned only one project ID).
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`/etc/projid` contains a mapping from named projects to project IDs.
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This proposal utilizes hard project quotas. Soft quotas are of no
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utility; they allow for temporary overage that, after a programmable
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period of time, is converted to the hard quota limit.
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This proposal utilizes hard project quotas for both monitoring _and
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enforcement_. Soft quotas are of no utility; they allow for temporary
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overage that, after a programmable period of time, is converted to the
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hard quota limit.
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## Motivation
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@ -190,7 +202,8 @@ spec:
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more of data before the housekeeping performed once per minute
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catches up to it. If the primary volume is the root partition, this
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will completely fill the partition, possibly causing serious
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problems elsewhere on the system.
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problems elsewhere on the system. This proposal does not address
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this issue; _a future enforcing project would_.
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In many environments, these issues may not matter, but shared
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multi-tenant environments need these issues addressed.
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@ -207,14 +220,6 @@ These goals apply only to local ephemeral storage, as described in
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files being held open.
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* Primary: this will not interfere with the more common user and group
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quotas.
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* Stretch: enforce limits on per-volume storage consumption by using
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enforced project quotas. Each volume would be given an enforced
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quota of the total ephemeral storage limit of the pod. _This will
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only be done if a mechanism is devised to allow quota enforcement on
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container writable layers; enforcement on emptydir volumes without
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such on writable layers does not restrict the user._ If we cannot
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do this, enforcing quotas will either be disabled or enabled by an
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optional feature gate that is disabled by default.
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### Non-Goals
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@ -228,6 +233,11 @@ These goals apply only to local ephemeral storage, as described in
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* Enforcing limits on total pod storage consumption by any means, such
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that the pod would be hard restricted to the desired storage limit.
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### Future Work
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* _Enforce limits on per-volume storage consumption by using
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enforced project quotas._
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## Proposal
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This proposal applies project quotas to emptydir volumes on qualifying
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@ -238,8 +248,8 @@ and attaching the ID to one or more files. By default (and as
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utilized herein), if a project ID is attached to a directory, it is
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inherited by any files created under that directory.
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If we elect to use the quota as enforcing, we impose a quota
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consistent with the desired limit. If we elect to use it as
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_If we elect to use the quota as enforcing, we impose a quota
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consistent with the desired limit._ If we elect to use it as
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non-enforcing, we impose a large quota that in practice cannot be
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exceeded (2^63-1 bytes for XFS, 2^58-1 bytes for ext4fs).
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@ -258,7 +268,8 @@ At present, three feature gates control operation of quotas:
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* `FSQuotaForLSCIEnforcement` must be enabled, in addition to
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`FSQuotaForLSCIMonitoring`, to use quotas for enforcement. This
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defaults to False and is expected to remain in that state for
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initial release.
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initial release. _A future project to use quotas for enforcing may
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change this default to True._
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### Operation Flow -- Applying a Quota
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@ -318,8 +329,8 @@ assigned a unique project ID (unless it is desired to pool the storage
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use of multiple directories).
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The canonical mechanism to record persistently that a project ID is
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reserved is to store it in the `/etc/projid` (projid[5]) and/or
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`/etc/projects` (projects(5)) files. However, it is possible to utilize
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reserved is to store it in the `/etc/projid` (`projid[5]`) and/or
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`/etc/projects` (`projects(5)`) files. However, it is possible to utilize
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project IDs without recording them in those files; they exist for
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administrative convenience but neither the kernel nor the filesystem
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is aware of them. Other ways can be used to determine whether a
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@ -455,8 +466,8 @@ required elsewhere:
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* The operation executor needs to pass the desired size limit to the
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volume plugin where appropriate so that the volume plugin can impose
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a quota. The limit is passed as 0 (do not use quotas), positive
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number (impose an enforcing quota if possible, measured in bytes),
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a quota. The limit is passed as 0 (do not use quotas), _positive
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number (impose an enforcing quota if possible, measured in bytes),_
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or -1 (impose a non-enforcing quota, if possible) on the volume.
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This requires changes to
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@ -526,13 +537,9 @@ appropriate end to end tests.
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behavior. For example, if a quota is incorrectly applied it could
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result in ability to write no data at all to the volume. This could
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be mitigated by use of non-enforcing quotas. XFS in particular
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offers the pqnoenforce mount option that makes all quotas
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offers the `pqnoenforce` mount option that makes all quotas
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non-enforcing.
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We should offer two feature gates, one to enable quotas at all (on
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by default) and one to enable enforcing quotas (initially off, but
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with intention of enabling in the near future).
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## Graduation Criteria
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@ -685,7 +692,7 @@ appeared promising, it turned out to have multiple critical flaws:
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```
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* If the filesystem is mounted `sync`, all writes to it are
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immediately committed to the backing store, and the _dd_ operation
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immediately committed to the backing store, and the `dd` operation
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above fails as soon as it fills up `/var/tmp/d1`. However,
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performance is drastically slowed, particularly with small writes;
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with 1K writes, I observed performance degradation in some cases
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@ -693,7 +700,7 @@ appeared promising, it turned out to have multiple critical flaws:
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I performed a test comparing writing 64 MB to a base (partitioned)
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filesystem, to a loop filesystem without `sync`, and a loop
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filesystem with _sync. Total I/O was sufficient to run for at least
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filesystem with `sync`. Total I/O was sufficient to run for at least
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5 seconds in each case. All filesystems involved were XFS. Loop
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filesystems were 128 MB and dense. Times are in seconds. The
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erratic behavior (e. g. the 65536 case) was involved was observed
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@ -729,3 +736,74 @@ appeared promising, it turned out to have multiple critical flaws:
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types are to be managed by different components, each such component
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needs access to the quota code. The code is substantial and should
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not be copied; it would more appropriately be vendored.
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## References
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### Bugs Opened Against Filesystem Quotas
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The following is a list of known security issues referencing
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filesystem quotas on Linux, and other bugs referencing filesystem
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quotas in Linux since 2012. These bugs are not necessarily in the
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quota system.
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#### CVE
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* *CVE-2012-2133* Use-after-free vulnerability in the Linux kernel
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before 3.3.6, when huge pages are enabled, allows local users to
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cause a denial of service (system crash) or possibly gain privileges
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by interacting with a hugetlbfs filesystem, as demonstrated by a
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umount operation that triggers improper handling of quota data.
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The issue is actually related to huge pages, not quotas
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specifically. The demonstration of the vulnerability resulted in
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incorrect handling of quota data.
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* *CVE-2012-3417* The good\_client function in rquotad (rquota\_svc.c)
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in Linux DiskQuota (aka quota) before 3.17 invokes the hosts\_ctl
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function the first time without a host name, which might allow
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remote attackers to bypass TCP Wrappers rules in hosts.deny (related
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to rpc.rquotad; remote attackers might be able to bypass TCP
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Wrappers rules).
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This issue is related to remote quota handling, which is not the use
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case for the proposal at hand.
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#### Other Security Issues Without CVE
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* [Linux Kernel Quota Flaw Lets Local Users Exceed Quota Limits and
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Create Large Files](https://securitytracker.com/id/1002610)
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A setuid root binary inheriting file descriptors from an
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unprivileged user process may write to the file without respecting
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quota limits. If this issue is still present, it would allow a
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setuid process to exceed any enforcing limits, but does not affect
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the quota accounting (use of quotas for monitoring).
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### Other Linux Quota-Related Bugs Since 2012
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* [ext4: report delalloc reserve as non-free in statfs mangled by
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project quota](https://lore.kernel.org/patchwork/patch/884530/)
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This bug, fixed in Feb. 2018, properly accounts for reserved but not
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committed space in project quotas. At this point I have not
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determined the impact of this issue.
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* [XFS quota doesn't work after rebooting because of
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crash](https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1461730)
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This bug resulted in XFS quotas not working after a crash or forced
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reboot. Under this proposal, Kubernetes would fall back to du for
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monitoring should a bug of this nature manifest itself again.
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* [quota can show incorrect filesystem
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name](https://bugzilla.redhat.com/show_bug.cgi?id=1326527)
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This issue, which will not be fixed, results in the quota command
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possibly printing an incorrect filesystem name when used on remote
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filesystems. It is a display issue with the quota command, not a
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quota bug at all, and does not result in incorrect quota information
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being reported. As this proposal does not utilize the quota command
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or rely on filesystem name, or currently use quotas on remote
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filesystems, it should not be affected by this bug.
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In addition, the e2fsprogs have had numerous fixes over the years.
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