From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on dcvr.yhbt.net X-Spam-Level: X-Spam-ASN: AS3215 2.6.0.0/16 X-Spam-Status: No, score=-3.4 required=3.0 tests=AWL,BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,T_SCC_BODY_TEXT_LINE shortcircuit=no autolearn=ham autolearn_force=no version=3.4.2 Received: from out1.vger.email (out1.vger.email [IPv6:2620:137:e000::1:20]) by dcvr.yhbt.net (Postfix) with ESMTP id 12CC91F729 for ; Mon, 27 Jun 2022 18:41:10 +0000 (UTC) Authentication-Results: dcvr.yhbt.net; dkim=pass (2048-bit key; unprotected) header.d=gmail.com header.i=@gmail.com header.b="FgzdqgcO"; dkim-atps=neutral Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237481AbiF0Sii (ORCPT ); Mon, 27 Jun 2022 14:38:38 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:37274 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S240496AbiF0SiM (ORCPT ); Mon, 27 Jun 2022 14:38:12 -0400 Received: from mail-wm1-x333.google.com (mail-wm1-x333.google.com [IPv6:2a00:1450:4864:20::333]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 96ABCCE2 for ; Mon, 27 Jun 2022 11:36:43 -0700 (PDT) Received: by mail-wm1-x333.google.com with SMTP id c130-20020a1c3588000000b0039c6fd897b4so8024747wma.4 for ; Mon, 27 Jun 2022 11:36:43 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=message-id:in-reply-to:references:from:date:subject:fcc :content-transfer-encoding:mime-version:to:cc; bh=YqoyexvLeD9VobWvJz7mGg0G5uZtp4Fx9wNnc+nZhXg=; b=FgzdqgcOSh4Lwr7B1tIlF45bUdJ7zRf56DWZU5m6rEQWk0OefOjbB387OaDjglPoux 29VZXznGXTb9y7uaEuA6hTbhArwVFpOSc0TsB8+tTmGX0vIFc0RRy1yLGnYFflI6NIEr BTIkpbz/a+Gn5dZ/8cTG1wAHfHdhGgitgZuo4F7NQ/+g+nMNW5vIeEBiyApfxmPszoP/ wrCfuyawrcBdzLhO9PYKXRJBlZNi4zoEAQBZ5Cn7x1c2H2r0h3Uf8OGathHpGgw69SUS lIbbaWYpGOwGCjx86sj1YUJEMdNC/R0nqux6TDtXXQex5ao8/ZZUMHoCiJV24sDTVuhr 8rYg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:message-id:in-reply-to:references:from:date :subject:fcc:content-transfer-encoding:mime-version:to:cc; bh=YqoyexvLeD9VobWvJz7mGg0G5uZtp4Fx9wNnc+nZhXg=; b=DrM+yjUDIroPIPWk/w6PbmOzo2HUTCU9+sF3vUU9/glco4d3YiSncKUnK8B6a7Yjig ltVDGSzjckpGhGmxWiN/vrtPpAXc7XrKC0AYEUaA8j7eBG0Odb6PHOG1sfRhi4bdaVgh PF0Q74BVG8I30Be1l57SCtPV+SRn2i77WNn0u4b4ioEMnij9gAPxYAduN56eU8kzw8vY j9SU082uvaEwKMjq6tW/HGRlFQXtCxtIIHHB/vgz3yWQmboMktLlNw3eKXuMWQYKTuD9 JMS+sErNI/9GaYdAV35ucaiB3lWHcwAzPxInEPOaKkRtPXtIW37TbT8Sh2IeponkMZ/P 7F4g== X-Gm-Message-State: AJIora9nW4xxGzEQu82ZQ6HOXyDR01Vj/24lvGxsCsfaG2071nPQh2i3 4sQiOdYZljRe6Y36rM95Gyd8VSVoiZlFew== X-Google-Smtp-Source: AGRyM1vW0xTcl9Vtoe87iP/V+UKnmIvGdLLM0LD6c3DfA+ca0YyGSKpIXSJc37KEFJYhWg9+w7+lLg== X-Received: by 2002:a7b:c110:0:b0:39c:8270:7b95 with SMTP id w16-20020a7bc110000000b0039c82707b95mr17094546wmi.41.1656355001749; Mon, 27 Jun 2022 11:36:41 -0700 (PDT) Received: from [127.0.0.1] ([13.74.141.28]) by smtp.gmail.com with ESMTPSA id ay4-20020a05600c1e0400b003a047dccfffsm6667120wmb.42.2022.06.27.11.36.40 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 27 Jun 2022 11:36:41 -0700 (PDT) Message-Id: <14411512783fd4e2cdcc8513690377b29262f6b8.1656354994.git.gitgitgadget@gmail.com> In-Reply-To: References: From: "Glen Choo via GitGitGadget" Date: Mon, 27 Jun 2022 18:36:34 +0000 Subject: [PATCH v5 5/5] setup.c: create `discovery.bare` Fcc: Sent Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit MIME-Version: 1.0 To: git@vger.kernel.org Cc: Taylor Blau , "brian m. carlson" , Derrick Stolee , Junio C Hamano , Emily Shaffer , Jonathan Tan , Glen Choo , Glen Choo Precedence: bulk List-ID: X-Mailing-List: git@vger.kernel.org From: Glen Choo There is a known social engineering attack that takes advantage of the fact that a working tree can include an entire bare repository, including a config file. A user could run a Git command inside the bare repository thinking that the config file of the 'outer' repository would be used, but in reality, the bare repository's config file (which is attacker-controlled) is used, which may result in arbitrary code execution. See [1] for a fuller description and deeper discussion. A simple mitigation is to forbid bare repositories unless specified via `--git-dir` or `GIT_DIR`. In environments that don't use bare repositories, this would be minimally disruptive. Create a config variable, `discovery.bare`, that tells Git whether or not to die() when it discovers a bare repository. This only affects repository discovery, thus it has no effect if discovery was not done, e.g. if the user passes `--git-dir=my-dir`, discovery will be skipped and my-dir will be used as the repo regardless of the `discovery.bare` value. This config is an enum of: - "always": always allow bare repositories (this is the default) - "never": never allow bare repositories If we want to protect users from such attacks by default, neither value will suffice - "always" provides no protection, but "never" is impractical for bare repository users. A more usable default would be to allow only non-embedded bare repositories ([2] contains one such proposal), but detecting if a repository is embedded is potentially non-trivial, so this work is not implemented in this series. [1]: https://lore.kernel.org/git/kl6lsfqpygsj.fsf@chooglen-macbookpro.roam.corp.google.com [2]: https://lore.kernel.org/git/5b969c5e-e802-c447-ad25-6acc0b784582@github.com Signed-off-by: Glen Choo --- Documentation/config.txt | 2 + Documentation/config/discovery.txt | 23 ++++++++++ setup.c | 57 ++++++++++++++++++++++++- t/t0035-discovery-bare.sh | 68 ++++++++++++++++++++++++++++++ 4 files changed, 149 insertions(+), 1 deletion(-) create mode 100644 Documentation/config/discovery.txt create mode 100755 t/t0035-discovery-bare.sh diff --git a/Documentation/config.txt b/Documentation/config.txt index e284b042f22..9a5e1329772 100644 --- a/Documentation/config.txt +++ b/Documentation/config.txt @@ -409,6 +409,8 @@ include::config/diff.txt[] include::config/difftool.txt[] +include::config/discovery.txt[] + include::config/extensions.txt[] include::config/fastimport.txt[] diff --git a/Documentation/config/discovery.txt b/Documentation/config/discovery.txt new file mode 100644 index 00000000000..bbcf89bb0b5 --- /dev/null +++ b/Documentation/config/discovery.txt @@ -0,0 +1,23 @@ +discovery.bare:: + Specifies whether Git will work with a bare repository that it + found during repository discovery. If the repository is + specified directly via the --git-dir command-line option or the + GIT_DIR environment variable (see linkgit:git[1]), Git will + always use the specified repository, regardless of this value. ++ +This config setting is only respected in protected configuration (see +<>). This prevents the untrusted repository from tampering with +this value. ++ +The currently supported values are: ++ +* `always`: Git always works with bare repositories +* `never`: Git never works with bare repositories ++ +This defaults to `always`, but this default may change in the future. ++ +If you do not use bare repositories in your workflow, then it may be +beneficial to set `discovery.bare` to `never` in your global config. +This will protect you from attacks that involve cloning a repository +that contains a bare repository and running a Git command within that +directory. diff --git a/setup.c b/setup.c index c8e3c32814d..16938fd5a24 100644 --- a/setup.c +++ b/setup.c @@ -10,6 +10,10 @@ static int inside_git_dir = -1; static int inside_work_tree = -1; static int work_tree_config_is_bogus; +enum discovery_bare_allowed { + DISCOVERY_BARE_NEVER = 0, + DISCOVERY_BARE_ALWAYS, +}; static struct startup_info the_startup_info; struct startup_info *startup_info = &the_startup_info; @@ -1142,6 +1146,46 @@ static int ensure_valid_ownership(const char *path) return data.is_safe; } +static int discovery_bare_cb(const char *key, const char *value, void *d) +{ + enum discovery_bare_allowed *discovery_bare_allowed = d; + + if (strcmp(key, "discovery.bare")) + return 0; + + if (!strcmp(value, "never")) { + *discovery_bare_allowed = DISCOVERY_BARE_NEVER; + return 0; + } + if (!strcmp(value, "always")) { + *discovery_bare_allowed = DISCOVERY_BARE_ALWAYS; + return 0; + } + return -1; +} + +static enum discovery_bare_allowed get_discovery_bare(void) +{ + enum discovery_bare_allowed result = DISCOVERY_BARE_ALWAYS; + git_protected_config(discovery_bare_cb, &result); + return result; +} + +static const char *discovery_bare_allowed_to_string( + enum discovery_bare_allowed discovery_bare_allowed) +{ + switch (discovery_bare_allowed) { + case DISCOVERY_BARE_NEVER: + return "never"; + case DISCOVERY_BARE_ALWAYS: + return "always"; + default: + BUG("invalid discovery_bare_allowed %d", + discovery_bare_allowed); + } + return NULL; +} + enum discovery_result { GIT_DIR_NONE = 0, GIT_DIR_EXPLICIT, @@ -1151,7 +1195,8 @@ enum discovery_result { GIT_DIR_HIT_CEILING = -1, GIT_DIR_HIT_MOUNT_POINT = -2, GIT_DIR_INVALID_GITFILE = -3, - GIT_DIR_INVALID_OWNERSHIP = -4 + GIT_DIR_INVALID_OWNERSHIP = -4, + GIT_DIR_DISALLOWED_BARE = -5, }; /* @@ -1248,6 +1293,8 @@ static enum discovery_result setup_git_directory_gently_1(struct strbuf *dir, } if (is_git_directory(dir->buf)) { + if (!get_discovery_bare()) + return GIT_DIR_DISALLOWED_BARE; if (!ensure_valid_ownership(dir->buf)) return GIT_DIR_INVALID_OWNERSHIP; strbuf_addstr(gitdir, "."); @@ -1394,6 +1441,14 @@ const char *setup_git_directory_gently(int *nongit_ok) } *nongit_ok = 1; break; + case GIT_DIR_DISALLOWED_BARE: + if (!nongit_ok) { + die(_("cannot use bare repository '%s' (discovery.bare is '%s')"), + dir.buf, + discovery_bare_allowed_to_string(get_discovery_bare())); + } + *nongit_ok = 1; + break; case GIT_DIR_NONE: /* * As a safeguard against setup_git_directory_gently_1 returning diff --git a/t/t0035-discovery-bare.sh b/t/t0035-discovery-bare.sh new file mode 100755 index 00000000000..0b345d361e6 --- /dev/null +++ b/t/t0035-discovery-bare.sh @@ -0,0 +1,68 @@ +#!/bin/sh + +test_description='verify discovery.bare checks' + +. ./test-lib.sh + +pwd="$(pwd)" + +expect_accepted () { + git "$@" rev-parse --git-dir +} + +expect_rejected () { + test_must_fail git "$@" rev-parse --git-dir 2>err && + grep "discovery.bare" err +} + +test_expect_success 'setup bare repo in worktree' ' + git init outer-repo && + git init --bare outer-repo/bare-repo +' + +test_expect_success 'discovery.bare unset' ' + ( + cd outer-repo/bare-repo && + expect_accepted + ) +' + +test_expect_success 'discovery.bare=always' ' + git config --global discovery.bare always && + ( + cd outer-repo/bare-repo && + expect_accepted + ) +' + +test_expect_success 'discovery.bare=never' ' + git config --global discovery.bare never && + ( + cd outer-repo/bare-repo && + expect_rejected + ) +' + +test_expect_success 'discovery.bare in the repository' ' + ( + cd outer-repo/bare-repo && + # Temporarily set discovery.bare=always, otherwise git + # config fails with "fatal: not in a git directory" + # (like safe.directory) + git config --global discovery.bare always && + git config discovery.bare always && + git config --global discovery.bare never && + expect_rejected + ) +' + +test_expect_success 'discovery.bare on the command line' ' + git config --global discovery.bare never && + ( + cd outer-repo/bare-repo && + expect_accepted -c discovery.bare=always && + expect_rejected -c discovery.bare= + ) +' + +test_done -- gitgitgadget