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78 lines
2.6 KiB
78 lines
2.6 KiB
4 months ago
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net_test v0.1
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=============
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A simple framework for blackbox testing of kernel networking code.
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Why use it?
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===========
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- Fast test / boot cycle.
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- Access to host filesystem and networking via L2 bridging.
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- Full Linux userland including Python, etc.
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- Kernel bugs don't crash the system.
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How to use it
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=============
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cd <kerneldir>
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path/to/net_test/run_net_test.sh <test>
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where <test> is the name of a test binary in the net_test directory. This can
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be an x86 binary, a shell script, a Python script. etc.
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How it works
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============
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net_test compiles the kernel to a user-mode linux binary, which runs as a
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process on the host machine. It runs the binary to start a Linux "virtual
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machine" whose root filesystem is the supplied Debian disk image. The machine
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boots, mounts the root filesystem read-only, runs the specified test from init, and then drops to a shell.
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Access to host filesystem
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=========================
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The VM mounts the host filesystem at /host, so the test can be modified and
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re-run without rebooting the VM.
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Access to host networking
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=========================
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Access to host networking is provided by tap interfaces. On the host, the
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interfaces are named <user>TAP0, <user>TAP1, etc., where <user> is the first
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10 characters of the username running net_test. (10 characters because
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IFNAMSIZ = 16). On the guest, they are named eth0, eth1, etc.
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net_test does not do any networking setup beyond creating the tap interfaces.
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IP connectivity can be provided on the host side by setting up a DHCP server
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and NAT, sending IPv6 router advertisements, etc. By default, the VM has IPv6
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privacy addresses disabled, so its IPv6 addresses can be predicted using a tool
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such as ipv6calc.
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The provided filesystem contains a DHCPv4 client and simple networking
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utilities such as ping[6], traceroute[6], and wget.
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The number of tap interfaces is currently hardcoded to two. To change this
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number, modify run_net_test.sh.
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Logging into the VM, installing packages, etc.
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==============================================
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net_test mounts the root filesystem read-only, and runs the test from init, but
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since the filesystem contains a full Linux userland, it's possible to boot into
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userland and modify the filesystem, for example to install packages using
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apt-get install. Log in as root with no password. By default, the filesystem is
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configured to perform DHCPv4 on eth0 and listen to RAs.
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Bugs
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====
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Since the test mounts the filesystem read-only, tests cannot modify
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/etc/resolv.conf and the system resolver is hardcoded to 8.8.8.8.
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