bug: ensure only secondary addresses are used when assigning aliases#65
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keithaws
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Aug 2, 2022
The `local-ipv4s` IMDS field lists the primary RFC 1918 address on the first line, with secondary IPv4 addresses on subsequent lines. When assigning alises, we want to only consider secondary IPv4 addresses, so we exclude the primary using `tail -n +2`. In order to ensure consistent ordering across invocations, even if IMDS returns secondary addresses in unspecified order, the list of secondaries is processed with `sort`. Prior to this change, we were performing the `sort` operation before the `tail -n +2` operation, meaning that a secondary address that sorted before the primary would be mistakenly interpreted as a primary address, and a secondary address could be mistaken for the primary address. See amazonlinux#63
keithaws
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Aug 2, 2022
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Issue #, if available: #63
Description of changes:
The
local-ipv4sIMDS field lists the primary RFC 1918 address on the first line, with secondary IPv4 addresses on subsequent lines. When assigning alises, we want to only consider secondary IPv4 addresses, so we exclude the primary usingtail -n +2. In order to ensure consistent ordering across invocations, even if IMDS returns secondary addresses in unspecified order, the list of secondaries is processed withsort. Prior to this change, we were performing thesortoperation before thetail -n +2operation, meaning that a secondary address that sorted before the primary would be mistakenly interpreted as a primary address, and a secondary address could be mistaken for the primary address.To fix this, we move the
sortoperation after thetail -n +2operation. Technically this could still be broken if IMDS ever stops returning the primary address on the first line of the output, but for now there is no better way to identify the primary address.By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.