From: Johannes Schindelin <johannes.schindelin@xxxxxx> As described in https://trojansource.codes/trojan-source.pdf, it is possible to abuse directional formatting (a feature of Unicode) to deceive human readers into interpreting code differently from compilers. For example, an "if ()" expression could be enclosed in a comment, but rendered as if it was outside of that comment. In effect, this could fool a reviewer into misinterpreting the code flow as benign when it is not. It is highly unlikely that Git's source code wants to contain such directional formatting in the first place, so let's just disallow it. Signed-off-by: Johannes Schindelin <johannes.schindelin@xxxxxx> --- ci: disallow directional formatting A couple days ago, I stumbled over https://siliconangle.com/2021/11/01/trojan-source-technique-can-inject-malware-source-code-without-detection/, which details an interesting social-engineering attack: it uses directional formatting in source code to pretend to human readers that the code does something different than it actually does. It is highly unlikely that Git's source code wants to contain such directional formatting in the first place, so let's disallow it. Technically, this is not exactly -rc material, but the paper was just published, and I want us to be safe. Changes since v2: * The pathspec excluding binary files is now used directly instead of doing the ls-files | xargs dance. * Corrected a code comment: my custom git grep was not PCRE-enabled, but Ubuntu's isn't. But git grep -P still does not understand \uNNNN. * Even if the *.po files currently pass the check, the script is now future-proof by excluding them. * Renamed the script to have the .bash extension, to indicate that it requires a Bashism (i.e. a printf that understands the \uNNNN syntax). Changes since v1: * The code was moved into a script in ci/. * We use git ls-files now to exclude files marked as binary in the Git attributes. Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-1071%2Fdscho%2Fcheck-for-utf-8-directional-formatting-v3 Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-1071/dscho/check-for-utf-8-directional-formatting-v3 Pull-Request: https://github.com/gitgitgadget/git/pull/1071 Range-diff vs v2: 1: bbf963695ba ! 1: 80447819de3 ci: disallow directional formatting @@ .github/workflows/main.yml: jobs: - uses: actions/checkout@v2 - run: ci/install-dependencies.sh - run: ci/run-static-analysis.sh -+ - run: ci/check-directional-formatting.sh ++ - run: ci/check-directional-formatting.bash sparse: needs: ci-config if: needs.ci-config.outputs.enabled == 'yes' - ## ci/check-directional-formatting.sh (new) ## + ## ci/check-directional-formatting.bash (new) ## @@ +#!/bin/bash + @@ ci/check-directional-formatting.sh (new) +# to deceive reviewers into interpreting code differently from the compiler. +# This is intended to run on an Ubuntu agent in a GitHub workflow. +# -+# `git grep` as well as GNU grep do not handle `\u` as a way to specify UTF-8. -+# A PCRE-enabled `git grep` would handle `\u` as desired, but Ubuntu does -+# not build its `git` packages with PCRE support. ++# To allow translated messages to introduce such directional formatting in the ++# future, we exclude the `.po` files from this validation. ++# ++# Neither GNU grep nor `git grep` (not even with `-P`) handle `\u` as a way to ++# specify UTF-8. +# +# To work around that, we use `printf` to produce the pattern as a byte +# sequence, and then feed that to `git grep` as a byte sequence (setting @@ ci/check-directional-formatting.sh (new) +# U+2066..U+2069: LRI, RLI, FSI and PDI +regex='(\u202a|\u202b|\u202c|\u202d|\u202e|\u2066|\u2067|\u2068|\u2069)' + -+! git ls-files -z ':(attr:!binary)' | -+LC_CTYPE=C xargs -0r git grep -Ele "$(LC_CTYPE=C.UTF-8 printf "$regex")" -- ++! LC_CTYPE=C git grep -El "$(LC_CTYPE=C.UTF-8 printf "$regex")" \ ++ -- ':(exclude,attr:binary)' ':(exclude)*.po' .github/workflows/main.yml | 1 + ci/check-directional-formatting.bash | 27 +++++++++++++++++++++++++++ 2 files changed, 28 insertions(+) create mode 100755 ci/check-directional-formatting.bash diff --git a/.github/workflows/main.yml b/.github/workflows/main.yml index 6ed6a9e8076..deda12db3a9 100644 --- a/.github/workflows/main.yml +++ b/.github/workflows/main.yml @@ -289,6 +289,7 @@ jobs: - uses: actions/checkout@v2 - run: ci/install-dependencies.sh - run: ci/run-static-analysis.sh + - run: ci/check-directional-formatting.bash sparse: needs: ci-config if: needs.ci-config.outputs.enabled == 'yes' diff --git a/ci/check-directional-formatting.bash b/ci/check-directional-formatting.bash new file mode 100755 index 00000000000..e6211b141aa --- /dev/null +++ b/ci/check-directional-formatting.bash @@ -0,0 +1,27 @@ +#!/bin/bash + +# This script verifies that the non-binary files tracked in the Git index do +# not contain any Unicode directional formatting: such formatting could be used +# to deceive reviewers into interpreting code differently from the compiler. +# This is intended to run on an Ubuntu agent in a GitHub workflow. +# +# To allow translated messages to introduce such directional formatting in the +# future, we exclude the `.po` files from this validation. +# +# Neither GNU grep nor `git grep` (not even with `-P`) handle `\u` as a way to +# specify UTF-8. +# +# To work around that, we use `printf` to produce the pattern as a byte +# sequence, and then feed that to `git grep` as a byte sequence (setting +# `LC_CTYPE` to make sure that the arguments are interpreted as intended). +# +# Note: we need to use Bash here because its `printf` interprets `\uNNNN` as +# UTF-8 code points, as desired. Running this script through Ubuntu's `dash`, +# for example, would use a `printf` that does not understand that syntax. + +# U+202a..U+2a2e: LRE, RLE, PDF, LRO and RLO +# U+2066..U+2069: LRI, RLI, FSI and PDI +regex='(\u202a|\u202b|\u202c|\u202d|\u202e|\u2066|\u2067|\u2068|\u2069)' + +! LC_CTYPE=C git grep -El "$(LC_CTYPE=C.UTF-8 printf "$regex")" \ + -- ':(exclude,attr:binary)' ':(exclude)*.po' base-commit: 0cddd84c9f3e9c3d793ec93034ef679335f35e49 -- gitgitgadget
