IPv4 should do longest prefix match for src ip selection

[Bhasker Hariharan]

Description

When a NIC has multiple suitable IP addresses the stack should select the best address. In case of IPv6 the stack does a proper source IP selection based on the IPv6 RFC. But for IPv4 the stack today picks the first IP address on the NIC.

The stack should do a longest prefix match to find the most suitable IPv4 address when picking the src IP.

See:

gvisor/pkg/tcpip/network/ipv4/ipv4.go

Line 1085 in ae089ad

 func (e *endpoint) AcquireOutgoingPrimaryAddress(remoteAddr tcpip.Address, allowExpired bool) stack.AddressEndpoint { 

vs

gvisor/pkg/tcpip/network/ipv6/ipv6.go

Line 1714 in 94b1c16

 func (e *endpoint) AcquireOutgoingPrimaryAddress(remoteAddr tcpip.Address, allowExpired bool) stack.AddressEndpoint { 

Steps to reproduce

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runsc version

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docker version (if using docker)

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uname

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kubectl (if using Kubernetes)

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repo state (if built from source)

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runsc debug logs (if available)

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[github-actions]

A friendly reminder that this issue had no activity for 120 days.

[Kevin Krakauer]

Fixed by fd95313, baf097a, and 19399cd.