credential: sanitize the user prompt

When asking the user interactively for credentials, we want to avoid
misleading them e.g. via control sequences that pretend that the URL
targets a trusted host when it does not.

While Git learned, over the course of the preceding commits, to disallow
URLs containing URL-encoded control characters by default, credential
helpers are still allowed to specify values very freely (apart from Line
Feed and NUL characters, anything is allowed), and this would allow,
say, a username containing control characters to be specified that would
then be displayed in the interactive terminal prompt asking the user for
the password, potentially sending those control characters directly to
the terminal. This is undesirable because control characters can be used
to mislead users to divulge secret information to untrusted sites.

To prevent such an attack vector, let's add a `git_prompt()` that forces
the displayed text to be sanitized, i.e. displaying question marks
instead of control characters.

Note: While this commit's diff changes a lot of `user@host` strings to
`user%40host`, which may look suspicious on the surface, there is a good
reason for that: this string specifies a user name, not a
<username>@<hostname> combination! In the context of t5541, the actual
combination looks like this: `user%40@127.0.0.1:5541`. Therefore, these
string replacements document a net improvement introduced by this
commit, as `user@host@127.0.0.1` could have left readers wondering where
the user name ends and where the host name begins.

Hinted-at-by: Jeff King <peff@peff.net>
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

1 files changed, 7 insertions, 7 deletions

diff --git a/t/t5550-http-fetch-dumb.sh b/t/t5550-http-fetch-dumb.sh
index 8f182a3cbf..5d0e394609 100755
--- a/t/t5550-http-fetch-dumb.sh
+++ b/t/t5550-http-fetch-dumb.sh
@@ -90,13 +90,13 @@ test_expect_success 'http auth can use user/pass in URL' '
 test_expect_success 'http auth can use just user in URL' '
 	set_askpass wrong pass@host &&
 	git clone "$HTTPD_URL_USER/auth/dumb/repo.git" clone-auth-pass &&
-	expect_askpass pass user@host
+	expect_askpass pass user%40host
 '
 
 test_expect_success 'http auth can request both user and pass' '
 	set_askpass user@host pass@host &&
 	git clone "$HTTPD_URL/auth/dumb/repo.git" clone-auth-both &&
-	expect_askpass both user@host
+	expect_askpass both user%40host
 '
 
 test_expect_success 'http auth respects credential helper config' '
@@ -114,14 +114,14 @@ test_expect_success 'http auth can get username from config' '
 	test_config_global "credential.$HTTPD_URL.username" user@host &&
 	set_askpass wrong pass@host &&
 	git clone "$HTTPD_URL/auth/dumb/repo.git" clone-auth-user &&
-	expect_askpass pass user@host
+	expect_askpass pass user%40host
 '
 
 test_expect_success 'configured username does not override URL' '
 	test_config_global "credential.$HTTPD_URL.username" wrong &&
 	set_askpass wrong pass@host &&
 	git clone "$HTTPD_URL_USER/auth/dumb/repo.git" clone-auth-user2 &&
-	expect_askpass pass user@host
+	expect_askpass pass user%40host
 '
 
 test_expect_success 'set up repo with http submodules' '
@@ -142,7 +142,7 @@ test_expect_success 'cmdline credential config passes to submodule via clone' '
 	set_askpass wrong pass@host &&
 	git -c "credential.$HTTPD_URL.username=user@host" \
 		clone --recursive super super-clone &&
-	expect_askpass pass user@host
+	expect_askpass pass user%40host
 '
 
 test_expect_success 'cmdline credential config passes submodule via fetch' '
@@ -153,7 +153,7 @@ test_expect_success 'cmdline credential config passes submodule via fetch' '
 	git -C super-clone \
 	    -c "credential.$HTTPD_URL.username=user@host" \
 	    fetch --recurse-submodules &&
-	expect_askpass pass user@host
+	expect_askpass pass user%40host
 '
 
 test_expect_success 'cmdline credential config passes submodule update' '
@@ -170,7 +170,7 @@ test_expect_success 'cmdline credential config passes submodule update' '
 	git -C super-clone \
 	    -c "credential.$HTTPD_URL.username=user@host" \
 	    submodule update &&
-	expect_askpass pass user@host
+	expect_askpass pass user%40host
 '
 
 test_expect_success 'fetch changes via http' '