terraform/internal/ipaddr
Martin Atkins c23a7fce4e lang/funcs: Preserve IP address leading zero behavior from Go 1.16
Go 1.17 includes a breaking change to both net.ParseIP and net.ParseCIDR
functions to reject IPv4 address octets written with leading zeros.

Our use of these functions as part of the various CIDR functions in the
Terraform language doesn't have the same security concerns that the Go
team had in evaluating this change to the standard library, and so we
can't justify an exception to our v1.0 compatibility promises on the same
sort of security grounds that the Go team used to justify their
compatibility exception.

For that reason, we'll now use our own fork of the Go library functions
which has the new check disabled in order to preserve the prior behavior.
We're taking this path, rather than pre-normalizing the IP address before
calling into the standard library, because an additional normalization
layer would be entirely new code and additional complexity, whereas this
fork is relatively minor in terms of code size and avoids any significant
changes to our own calls to these functions.

Thanks to the Kubernetes team for their prior work on carving out a subset
of the "net" package for their similar backward-compatibility concern.
Our "ipaddr" package here is a lightly-modified fork of their fork, with
only the comments changed to talk about Terraform instead of Kubernetes.

This fork is not intended for use in any other future feature
implementations, because they wouldn't be subject to the same
compatibility constraints as our existing functions. We will use these
forked implementations for new callers only if consistency with the
behavior of the existing functions is a key requirement.
2021-08-17 15:20:05 -07:00
..
LICENSE
PATENTS
README.md
doc.go
ip.go
ip_test.go
parse.go

README.md

Forked IP address parsing functions

This directory contains a subset of code from the Go project's net package as of Go 1.16, used under the Go project license which we've included here in LICENSE and PATENTS, which are also copied from the Go project.

Terraform has its own fork of these functions because Go 1.17 included a breaking change to reject IPv4 address octets written with leading zeros.

The Go project rationale for that change was that Go historically interpreted leading-zero octets inconsistently with many other implementations, trimming off the zeros and still treating the rest as decimal rather than treating the octet as octal.

The Go team made the reasonable observation that having a function that interprets a non-normalized form in a manner inconsistent with other implementations may cause naive validation or policy checks to produce incorrect results, and thus it's a potential security concern. For more information, see Go issue #30999.

After careful consideration, the Terraform team has concluded that Terraform's use of these functions as part of the implementation of the cidrhost, cidrsubnet, cidrsubnets, and cidrnetmask functions has a more limited impact than the general availability of these functions in the Go standard library, and so we can't justify a similar exception to our Terraform 1.0 compatibility promises as the Go team made to their Go 1.0 compatibility promises.

If you're considering using this package for new functionality other than the built-in functions mentioned above, please do so only if consistency with the behavior of those functions is important. Otherwise, new features are not burdened by the same compatibility constraints and so should typically prefer to use the stricter interpretation of the upstream parsing functions.