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fix(net): validate TAP MTU and make VIRTIO_NET_F_MTU optional - #553
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Coverage Report for CI Build 43395750689Coverage increased (+0.2%) to 44.348%Details
Uncovered Changes
Coverage RegressionsNo coverage regressions found. Coverage Stats
💛 - Coveralls |
Net::new() unconditionally offered VIRTIO_NET_F_MTU with
TapNetSpec::mtu as config.mtu. When mtu was set below 68, the device
advertised VIRTIO_NET_F_MTU with an invalid config.mtu, violating
VirtIO 1.4 Sec 5.1.4.1 ("The device MUST set mtu to between 68 and
65535 inclusive, if it offers VIRTIO_NET_F_MTU"). Linux tolerates it
by not accepting VIRTIO_NET_F_MTU if config.mtu is below 68.
Make TapNetSpec::mtu optional on the command line, defaulting to 0.
When it is 0, set config.mtu to 0 and omit NetFeature::MTU from the
device features. Otherwise validate mtu >= 68 before opening the TAP
device and return Error::InvalidMtu if it is smaller.
Signed-off-by: Changyuan Lyu <changyuanl@google.com>
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Summary
Net::new()unconditionally advertisedVIRTIO_NET_F_MTUwithTapNetSpec::mtuasconfig.mtu. Whenmtuwas configured below68, the device exposedVIRTIO_NET_F_MTUwith an out-of-rangeconfig.mtu, violating VirtIO 1.4 Sec 5.1.4.1 ("The device MUST setmtuto between 68 and 65535 inclusive, if it offersVIRTIO_NET_F_MTU"). Linux tolerates it:virtnet_validate()does not acceptVIRTIO_NET_F_MTUifconfig.mtuis below 68.Changes
TapNetSpec::mtuau16and make it optional on the command line (0by default).mtuis0, setconfig.mtu = 0and do not advertiseNetFeature::MTU.mtu >= 68(MIN_MTU) before opening the TAP device and returnvirtio::Error::InvalidMtu { mtu }on invalid values; advertiseNetFeature::MTUwhen valid.alioth/src/virtio/dev/net/tap_test.rs(running without root or/dev/net/tun) and a CLI net parsing test withoutmtuinalioth-cli/src/boot/boot_test.rs.