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[PATCH v3 1/2] remote: create fetch.credentialsInUrl config

From
Derrick Stolee via GitGitGadget <gitgitgadget@gmail.com>
Date
Jun 1, 2022, 01:16 UTC
Message-ID
<083a918e9b1474eff0d51c4502b6d54de9b63764.1654046173.git.gitgitgadget@gmail.com>
In-Reply-To
<pull.1237.v3.git.1654046173.gitgitgadget@gmail.com>
From: Derrick Stolee <derrickstolee@github.com>

Users sometimes provide a "username:password" combination in their plaintext URLs. Since Git stores these URLs in plaintext in the .git/config file, this is a very insecure way of storing these credentials. Credential managers are a more secure way of storing this information.

System administrators might want to prevent this kind of use by users on their machines.

Create a new "fetch.credentialsInUrl" config option and teach Git to warn or die when seeing a URL with this kind of information. The warning anonymizes the sensitive information of the URL to be clear about the issue.

This change currently defaults the behavior to "allow" which does nothing with these URLs. We can consider changing this behavior to "warn" by default if we wish. At that time, we may want to add some advice about setting fetch.credentialsInUrl=ignore for users who still want to follow this pattern (and not receive the warning).

An earlier version of this change injected the logic into url_normalize() in urlmatch.c. While most code paths that parse URLs eventually normalize the URL, that normalization does not happen early enough in the stack to avoid attempting connections to the URL first. By inserting a check into the remote validation, we identify the issue before making a connection. In the old code path, this was revealed by testing the new t5601-clone.sh test under --stress, resulting in an instance where the return code was 13 (SIGPIPE) instead of 128 from the die().

Since we are not deep within url_normalize(), we need to do our own parsing to detect if there is a "username:password@domain" section. We begin by detecting the first '@' symbol in the URL. We then detect if there is a scheme such as "https://" by finding the first slash. If that slash does not exist or is after the first '@' symbol, then we consider the scheme to be complete before the URL. Finally, we look for a colon between the scheme and the '@' symbol, indicating a "username:password" string. Replace the password with "<redacted>" when writing the error message.

As an attempt to ensure the parsing logic did not catch any unintentional cases, I modified this change locally to to use the "die" option by default. Running the test suite succeeds except for the explicit username:password URLs used in t5550-http-fetch-dumb.sh and t5541-http-push-smart.sh. This means that all other tested URLs did not trigger this logic.

Signed-off-by: Derrick Stolee <derrickstolee@github.com>
---
 Documentation/config/fetch.txt | 14 ++++++++++
 remote.c                       | 48 ++++++++++++++++++++++++++++++++++
 t/t5601-clone.sh               | 14 ++++++++++
 3 files changed, 76 insertions(+)
diff --git a/Documentation/config/fetch.txt b/Documentation/config/fetch.txt
index cd65d236b43..0db7fe85bb8 100644
--- a/Documentation/config/fetch.txt
+++ b/Documentation/config/fetch.txt
@@ -96,3 +96,17 @@ fetch.writeCommitGraph::
 	merge and the write may take longer. Having an updated commit-graph
 	file helps performance of many Git commands, including `git merge-base`,
 	`git push -f`, and `git log --graph`. Defaults to false.
+
+fetch.credentialsInUrl::
+	A URL can contain plaintext credentials in the form
+	`<protocol>://<user>:<password>@<domain>/<path>`. Using such URLs
+	is not recommended as it exposes the password in multiple ways,
+	including Git storing the URL as plaintext in the repository config.
+	The `fetch.credentialsInUrl` option provides instruction for how Git
+	should react to seeing such a URL, with these values:
++
+* `allow` (default): Git will proceed with its activity without warning.
+* `warn`: Git will write a warning message to `stderr` when parsing a URL
+  with a plaintext credential.
+* `die`: Git will write a failure message to `stderr` when parsing a URL
+  with a plaintext credential.
diff --git a/remote.c b/remote.c
index 42a4e7106e1..accf08bf51f 100644
--- a/remote.c
+++ b/remote.c
@@ -22,8 +22,56 @@ struct counted_string {
 	const char *s;
 };
 
+/*
+ * Check if the given URL is of the following form:
+ *
+ *     scheme://username:password@domain[:port][/path]
+ *
+ * Specifically, see if the ":password@" section of the URL appears.
+ *
+ * The fetch.credentialsInUrl config indicates what to do on such a URL,
+ * either ignoring, warning, or erroring. The latter two modes write a
+ * redacted URL to stderr.
+ */
+static void check_if_creds_in_url(const char *url)
+{
+	const char *value, *scheme_ptr, *colon_ptr, *at_ptr;
+	struct strbuf redacted = STRBUF_INIT;
+
+	/* "allow" is the default behavior. */
+	if (git_config_get_string_tmp("fetch.credentialsinurl", &value) ||
+	    !strcmp("allow", value))
+		return;
+
+	if (!(at_ptr = strchr(url, '@')))
+		return;
+
+	if (!(scheme_ptr = strchr(url, '/')) ||
+	    scheme_ptr > at_ptr)
+		scheme_ptr = url;
+
+	if (!(colon_ptr = strchr(scheme_ptr, ':')))
+		return;
+
+	/* Include the colon when creating the redacted URL. */
+	colon_ptr++;
+	strbuf_addstr(&redacted, url);
+	strbuf_splice(&redacted, colon_ptr - url, at_ptr - colon_ptr,
+		      "<redacted>", 10);
+
+	if (!strcmp("warn", value))
+		warning(_("URL '%s' uses plaintext credentials"), redacted.buf);
+	if (!strcmp("die", value))
+		die(_("URL '%s' uses plaintext credentials"), redacted.buf);
+
+	strbuf_release(&redacted);
+}
+
 static int valid_remote(const struct remote *remote)
 {
+	for (int i = 0; i < remote->url_nr; i++)
+		check_if_creds_in_url(remote->url[i]);
+
 	return (!!remote->url) || (!!remote->foreign_vcs);
 }
 
diff --git a/t/t5601-clone.sh b/t/t5601-clone.sh
index 4a61f2c901e..cba3553b7c4 100755
--- a/t/t5601-clone.sh
+++ b/t/t5601-clone.sh
@@ -71,6 +71,20 @@ test_expect_success 'clone respects GIT_WORK_TREE' '
 
 '
 
+test_expect_success 'clone warns or fails when using username:password' '
+	test_must_fail git -c fetch.credentialsInUrl=allow clone https://username:password@localhost attempt1 2>err &&
+	! grep "URL '\''https://username:<redacted>@localhost'\'' uses plaintext credentials" err &&
+	test_must_fail git -c fetch.credentialsInUrl=warn clone https://username:password@localhost attempt1 2>err &&
+	grep "warning: URL '\''https://username:<redacted>@localhost'\'' uses plaintext credentials" err &&
+	test_must_fail git -c fetch.credentialsInUrl=die clone https://username:password@localhost attempt2 2>err &&
+	grep "fatal: URL '\''https://username:<redacted>@localhost'\'' uses plaintext credentials" err
+'
+
+test_expect_success 'clone does not detect username:password when it is https://username@domain:port/' '
+	test_must_fail git -c fetch.credentialsInUrl=warn clone https://username@localhost:8080 attempt3 2>err &&
+	! grep "uses plaintext credentials" err
+'
+
 test_expect_success 'clone from hooks' '
 
 	test_create_repo r0 &&

-- 
gitgitgadget
Previous: Derrick Stolee via GitGitGadgetNext: Ævar Arnfjörð Bjarmason
Message 23 of 40 in “urlmatch: create fetch.credentialsInUrl config”
  1. urlmatch: create fetch.credentialsInUrl configDerrick Stolee via GitGitGadget, May 23, 2022
  2. Junio C HamanoMay 23, 2022
  3. Derrick StoleeMay 23, 2022
  4. Junio C HamanoMay 23, 2022
  5. Johannes SchindelinMay 24, 2022
  6. Derrick StoleeMay 24, 2022
  7. Junio C HamanoMay 23, 2022
  8. Johannes SchindelinMay 24, 2022
  9. Ævar Arnfjörð BjarmasonMay 24, 2022
  10. Derrick StoleeMay 24, 2022
  11. Ævar Arnfjörð BjarmasonMay 24, 2022
  12. Derrick StoleeMay 25, 2022
  13. Johannes SchindelinMay 24, 2022
  14. Derrick StoleeMay 24, 2022
  15. urlmatch: create fetch.credentialsInUrl configDerrick Stolee via GitGitGadget, May 27, 2022
  16. Ævar Arnfjörð BjarmasonMay 27, 2022
  17. Derrick StoleeMay 27, 2022
  18. Junio C HamanoMay 27, 2022
  19. Junio C HamanoMay 27, 2022
  20. Junio C HamanoMay 30, 2022
  21. Derrick StoleeMay 31, 2022
  22. 0/2 fetch: create fetch.credentialsInUrl configDerrick Stolee via GitGitGadget, Jun 1, 2022
  23. 1/2 remote: create fetch.credentialsInUrl configDerrick Stolee via GitGitGadget, Jun 1, 2022
  24. Ævar Arnfjörð BjarmasonJun 1, 2022
  25. Derrick StoleeJun 2, 2022
  26. 2/2 usage: add warn_once() helper for repeated warningsDerrick Stolee via GitGitGadget, Jun 1, 2022
  27. Ævar Arnfjörð BjarmasonJun 1, 2022
  28. Derrick StoleeJun 1, 2022
  29. Ævar Arnfjörð BjarmasonJun 1, 2022
  30. Derrick StoleeJun 2, 2022
  31. Junio C HamanoJun 1, 2022
  32. Derrick StoleeJun 2, 2022
  33. Junio C HamanoJun 2, 2022
  34. Junio C HamanoJun 1, 2022
  35. remote: create fetch.credentialsInUrl configDerrick Stolee via GitGitGadget, Jun 2, 2022
  36. Junio C HamanoJun 2, 2022
  37. Derrick StoleeJun 3, 2022
  38. Junio C HamanoJun 6, 2022
  39. remote: create fetch.credentialsInUrl configDerrick Stolee via GitGitGadget, Jun 6, 2022
  40. Junio C HamanoJun 6, 2022

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