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Update on Overleaf.
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report.tex
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report.tex
@ -336,23 +336,23 @@ Inter-Process Communication (IPC) namespaces isolate two Linux IPC mechanisms wh
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\say{Objects created in an IPC namespace are visible to all other processes that are members of that namespace, but are not visible to processes in other IPC namespaces.}
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This provides exactly the correct semantics for a void process. IPC objects are visible within a namespace if and only if they are created within that namespace. Therefore, a new namespace is entirely empty, and no more work need be done. IPC namespaces represent a relatively small attack surface and appear to function well as a namespace (a series of searches revealed no results). Similarly, the historical SysV IPC and POSIX message queues that are isolated show very few bugs. One was found (CVE-2015-7613) which describes a race condition leading to escalated privilege. From the limited information available, it seems that namespacing and hence void processes protect well against this, as the escalated privilege is isolated to the calling namespace.
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This provides exactly the correct semantics for a void process. IPC objects are visible within a namespace if and only if they are created within that namespace. Therefore, a new namespace is entirely empty, and no more work need be done. IPC namespaces represent a relatively small attack surface and appear to function well as a namespace (a series of searches revealed no results). Similarly, the mature SysV IPC and POSIX message queues that are isolated show very few bugs. One was found (CVE-2015-7613) which describes a race condition leading to escalated privilege. Namespacing and hence void processes protect well against this, as the escalated privilege is isolated to the calling namespace.
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\section{UTS namespaces}
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\label{sec:voiding-uts}
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Unix-Time Sharing (UTS) namespaces provide isolation of the hostname and domain name of a system between processes. This is useful when creating containers, such that each container can appear as a different machine. Unlike IPC namespaces, UTS namespaces inherit their initial values. Each of the hostname and domain name in the new namespace is initialised to the values of the parent namespace.
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Unix-Time Sharing (UTS) namespaces provide isolation of the hostname and domain name of a system between processes. This is useful when creating containers, such that each container can appear as a different machine. UTS namespaces inherit their initial values - each of the hostname and domain name in the new namespace is initialised to the values of the parent namespace.
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As the inherited value does give information about the world outside of the void process, slightly more must be done than placing the process in a new namespace. This is simple for UTS namespaces, as the host name and domain name can be set to constants, removing any link to the parent. Although the implementation of this is trivial, it highlights how easy the information passed between namespaces is to miss if manually implementing process isolation.
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Slightly more must be done than creating a new namespace to avoid information leakage. This is simple for UTS namespaces, as the host name and domain name can be set to constants, removing any link to the parent. Although the implementation of this is trivial, it highlights how easy the information passed between namespaces is to miss if manually implementing process isolation.
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\section{Time namespaces}
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\label{sec:voiding-time}
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Time namespaces are the final namespace added at the time of writing, added in kernel version 5.6 \citep{linux_kernel_newbies_editors_linux_2020}. The motivation for adding time namespaces is given in the manual page \citep{free_software_foundation_time_namespaces7_2021}:
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Time namespaces are the final namespace added at the time of writing, added in kernel version 5.6 \citep{linux_kernel_newbies_editors_linux_2020}. They are motivated in the manual page \citep{free_software_foundation_time_namespaces7_2021}:
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\say{The motivation for adding time namespaces was to allow the monotonic and boot-time clocks to maintain consistent values during container migration and checkpoint/restore.}
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That is, time namespaces virtualise the appearance of system uptime to processes. They do not attempt to virtualise wall clock time. This is important for processes that depend on time in primarily one situation: migration. If an uptime dependent process is migrated from a machine that has been up for a week to a machine that was booted a minute ago, the guarantees provided by the clocks \texttt{CLOCK\_MONOTONIC} and \texttt{CLOCK\_BOOTTIME} no longer hold. This results in time namespaces having very limited usefulness in a system that does not support migration, such as the one presented here. Perhaps randomised offsets would hide some information about the system, but the usefulness is limited. Time namespaces are thus avoided in this implementation.
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That is, time namespaces virtualise the appearance of system uptime to processes. They do not attempt to virtualise wall clock time. This is important for processes that depend on time in primarily one situation: migration. If an uptime dependent process is migrated from a machine that has been up for a week to a machine that was booted a minute ago, the guarantees provided by the clocks \texttt{CLOCK\_MONOTONIC} and \texttt{CLOCK\_BOOTTIME} no longer hold. This results in time namespaces having very limited usefulness in a system that does not support migration, such as the one presented here. Time namespaces are thus avoided in this implementation.
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Searching the list of released CVEs for both ``clock" and ``time linux" (``time" itself revealed too many results to parse) shows no vulnerabilities in the time subsystem on Linux, or time namespaces themselves. This supports not including time namespaces at this stage, as their range is very limited, particularly in terms of isolation from vulnerabilities.
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